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The Pharmacogenetics behind Polymorphisms of the Immunoglobin G
Fragment C Receptor and Efficacy of Monoclonal Antibody
Treatments for Different Cancers.
“Can a patient’s DNA sequence be holding the answer to if their cancer treatment will be successful?
Pharmacogenetics provides the key…”
Thesis - September-October 2010
By Andriana (Andrea) Karambela, 3317331 CGDB Masters Program
Supervised by Dr. M.P.J.K. Lolkema, UMC Utrecht, Oncology Department
Table of contents
ABSTRACT ................................................................................................................ 4
1. INTRODUCTION .................................................................................................... 5
1.1 MAb Cancer Therapy: Modes of Action ....................................................................................................... 5
1.1.1 Signal Transduction Interference as an Anti-tumor Mechanism
1.1.2 ADCC and CDC May be Responsible for Efficacy of Some mAb Treatments
5
5
1.2 Treatment of Cancers with mAbs .................................................................................................................. 9
1.2.1 mAbs with Targets on Solid Tumors
1.2.2 mAbs with Lymphoma Targets
1.2.3 mAbs with Targets in the Tumor Stroma
1.2.4 mAbs with Ligand Targets
9
10
10
10
1.3 Evaluating Treatment Outcomes ................................................................................................................. 11
2. RESULTS ............................................................................................................. 13
2.1 Population frequencies of FcγR polymorphisms ........................................................................................ 14
2.2 FcγRIIa-131 polymorphisms and mAb efficacy ......................................................................................... 14
2.3 FcγRIIIa-158 polymorphisms and mAb efficacy ........................................................................................ 15
2.4 FcγRIIb-232 polymorphisms and mAb efficacy ......................................................................................... 17
2.5 FcγRIIIa-818 and FcγRIIa-535 polymorphisms and mAb efficacy .......................................................... 17
3. DISCUSSION ....................................................................................................... 19
Frequency of FcγR Genotypes in Populations .................................................................................................. 19
FcγRIIIa-158 Tumor response doesn’t necessarily correlate with increased Clinical Benefit ..................... 19
Response and PFS
V/V and V-carrier Lymphoma and Breast Cancer Patients Display Better Responses
Conflicting results concerning Cetuximab-Treated mCRC
Rarely Does Better Response Also Correlate with Better PFS
High Threshold for ADCC-induction?
19
19
20
20
21
FcγRIIa-131 ......................................................................................................................................................... 21
Polymorphism Usually does not Correlate with Response
PFS
Stable Disease May Be a Better Indicator of Longer PFS than CR/PR
Confounding Effects of Using Combination Treatments
FcγRIIb-232 Polymorphism may not Influence mAb Efficacy
21
22
22
23
23
FcγRIIIa-818A/A Cetuximab-treated CRC Patients More Likely to Have Longer PFS
Response is a Reliable Read-out?
Why Does FcγRIIIa-158 Genotype Correlate with Response in Lymphoma Patients but not Leukemia?
23
24
24
4. CONCLUSION ..................................................................................................... 25
SUPPLEMENTAL DATA ......................................................................................... 26
Table of Experimental Designs .......................................................................................................................... 26
FcγRIIIa-158 ........................................................................................................................................................ 27
Weng Study (2003)
Zhang Study (2010)
Farag Study
Bibeau Study
Zhang Study (2007)
Paez Study
Cartron Study
27
27
27
27
28
28
28
FcγRIIa-131 ......................................................................................................................................................... 28
Weng Study (2003)
Mitrovic Study
Kim Study
Dornan Study
Zhang Study (2007)
Paez Study
Musolino Study
28
29
29
29
29
30
30
FcγRIIb-232 ......................................................................................................................................................... 30
Musolino Study (2008)
Weng Study (2009)
30
30
FcγRIIIa-818 and FcγRIIa-535 .......................................................................................................................... 31
Pander Study
31
LITERATURE CITED ............................................................................................... 32
Abstract
The vertebrate immune system has evolved to become particularly good at protecting
an organism from extrinsic pathogens such as bacterial and fungal infections. Today the
cutting edge of medicine is trying to manipulate the immune system of cancer patients into
attacking their own cancerous cells. This can be facilitated through the use of monoclonal
antibody (mAb) treatments targeted towards tumor cell receptors or ligands that are
responsible for the flourishing of particular types of cancers. It has been postulated that mAb
treatments may work by stimulating the patient’s immune system to kill cancerous cells
through antibody-dependent cell-mediated cytotoxicity (ADCC). This process may be
responsible in part for the efficacy of these antibody treatments. Curiously, the response of
tumors to mAbs varies amongst patients. One hypothesis for this stratification amongst
patients is that polymorphisms within immune cell receptor genes can influence the affinity of
the immune cells to the mAb and hence may control how well the immune system attacks
cancer cells.
Our study focuses on the relationship between the efficacy of monoclonal antibodies
currently used in the clinic for treatment of solid and hematological cancers and
polymorphism of the immunoglobin G fragment C receptor. Using 14 studies as evidence, it
appears that there is not a clear cut answer for a relationship between FcγR polymorphisms
and efficacy of mAb treatment. Perhaps this is due to the many different kinds of
combinational therapies which are used in the clinic. However the trend seems to be that the
FcγRIIIa-158V/V genotype does improve response to treatment and can provide a longer
progression-free survival (PFS) of lymphoma and breast cancer patients. For the FcγRIIa-131
polymorphism, it appears H-carriers can have a longer median PFS than other patients
regardless of tumor response status. We did find that mAb treatments do not correspond with
FcR polymorphisms in patients with chronic lymphocytic leukemia. Furthermore we find that
“stable disease” classification can be linked with longer PFS and could therefore potentially
be considered a good prognostic indicator for clinical benefit. Further research needs to be
done, potentially with larger patient cohorts and proper controls to come to a definitive
answer on if the FcR polymorphisms are a useful predictor of tumor response to mAb
treatment.
1. Introduction
1.1 MAb Cancer Therapy: Modes of Action
Monoclonal antibodies (mAb) are an effective means to treat many different types of
cancer. Our study investigates if a cancer patients’ genotype for particular polymorphisms
significantly changes their response to or enhances their survival after mAb treatment.
1.1.1 Signal Transduction Interference as an Anti-tumor Mechanism
Some mAb treatments are effective due to their ability to block target function.
Targets have been specifically chosen as they contribute to tumor growth or sustainability, an
example being growth factor receptors. Use of mAbs targeting such receptors can attenuate
tumor growth and can even make the tumor cells sensitive to chemotherapeutic drugs. At the
molecular level these mAbs act by blocking activating ligands from binding to receptors and
sterically preventing dimerization of the receptor, and in some cases can even promote
cellular internalization of the receptor, like the mAb cetuximab (Sunada et al., 1986; Li et al.,
2005). Alternatively mAbs can act by blocking ligand-bound receptors from forming dimers
with other receptors which normally causes activation; such is the mechanism of the mAb
pertuzumab (Franklin et al., 2004). While signal transduction interference may be the primary
mode of action of mAbs, there may exist others.
1.1.2 ADCC and CDC May be Responsible for Efficacy of Some mAb
Treatments
Besides blocking target function, mAb may also promote the killing of tumor cells by
activation of the immune system.
Antibody Structure
Antibodies are heterodimers made of two light chains and two heavy chains (Strome et
al., 2007). Complementarity-determining regions are the amino terminus of each heavy and
light chain, and are comprised of variable amino acid sequences that give the antibody its
target specificity. The rest of the antibody contains relatively little variation in sequence and
is called the constant region (Fc).
Originally therapeutic mAb were of murine origin and their efficacy was not as high as
expected, as human immune responses to the murine antibody produced minimal beneficial
effects. However with the creation of chimeric mAbs which grafted the human Fc region
onto the murine backbone containing the variable region, this problem was counter-acted and
the efficacy of mAb treatments became higher (Adams and Weiner, 2005). Humanized mAb
accomplished similar results but instead used a human mAb backbone and grafted on the
murine variable regions.
Most therapeutic mAb are humanized using the IgG1 isotype as a backbone. The Fc
region of this immunoglobin can evoke a response of the human immune system to fight the
cancer, namely antibody-dependent cell-mediated cytotoxicity (ADCC), as well as
complement-dependent cytotoxicity (CDC).
ADCC
Antibody-dependent cell-mediated cytotoxicity (ADCC) is thought to be able to
influence the immune system’s adaptive response against tumor cells through therapeutic
mAb treatments (Adams and Weiner, 2005). The first step in this process is the binding of the
mAb to a tumor cell antigen. A Natural Killer cell (NK) can then bind through its Fc receptor
to the Fc region of the bound-mAb. Once receptors on the NK cell are crosslinked, this
initiates a cascade that releases granzymes and perforin which lyse the tumor cell. The tumor
cell debris is taken up by antigen-presenting cells. Once presented to B cells, antibodies can
be produced against numerous antigens of the tumor. Also, cytotoxic T lymphocytes can be
targeted to the tumor antigens and facilitate killing of the tumor cells.
This process causes an immediate destruction of tumor cells with latent anti-tumor
effects caused by adaptive immunity. This process can be mediated through the binding of the
mAb to the receptor of the effector cell. It has been thought that polymorphisms of the FcRs
can be an important regulator of tumor shrinkage if they interfere with the affinity of the
receptor for the mAb, which will be expanded upon later.
Complement-dependent Cytotoxicity
Another immune system pathway capable of killing tumor cells is complementdependent cytotoxicity (CDC). It is also thought to be partially induced through the use of
certain mAb treatments.
IgG1 and IgG3 can probably activate this system through the
complement activation pathway (Adams and Weiner, 2005). The pathway is initiated when
the mAb binds to the tumor cell and a conformation change in the structure of the mAb allows
for CDC proteins to bind to it and the CDC cascade begins. Ultimately the cascade ends with
the formation of the membrane attack complex (MAC). The MAC is capable of creating holes
within the membrane of the tumor cell allowing water and solutes to flow freely in and out
leading to the tumor cell’s demise.
One study shows that the CDC pathway does contribute to efficacy in vivo of
rituximab treatment. They show that mice inoculated with lymphoma cells were not able to be
cured with rituximab when the complement system was disrupted (Di Gaetano et al., 2003).
Both ADCC and CDC are mediated through FcRs of effector cells. This is why
polymorphisms of the FcRs has been focused upon in an effort to determine if it is a source of
the variation in response amongst patient’s treated with certain mAb.
Fcγ Receptors
Fcγ receptors (FcγR) are important for promoting and regulating immune response to
immune complexes, as the Fc region of IgG is recognized by the FcγR of effector immune
cells. In humans there are three classes of FcγRs expressed by immune cells: FcγRI, FcγRII
and FcγRIII. Furthermore there are “a”, “b” and “c” forms of FcγRII and “a”, “b” forms of
FcγRIII. The receptors are different functionally. The activating FcγRs will incite
cytotoxicity, and include FcγRIIA, FcγRIIC,
FcγRIIIA and
FcγRIIIB (Smith and
Clatworthy, 2010). FcγRIIA and FcγRIIIA are the receptors pertinent to our investigation.
FcγRIIB is the only receptor that when activated, inhibits cytotoxicity signaling and is also
discussed here. A receptor’s expression is restricted to certain cell types which further
discriminate the receptor’s functional specificity (Table 1).
One study showed that the FcγR of effector cells is important for effectiveness of
antibody treatments against tumors in mice. They tested the efficacy of trastuzumab and
rituxan on eradicating human tumor xenographs in mice lacking various FcγRs. They found
that the mechanism of efficacy of the mAb treatments was through minimal binding to
FCgammaRIIB (anti-ADCC receptor), while preferentially binding to the FcgammaRIII (proADCC) (Clynes et al., 2000). The anti-tumor effects of the mAb treatment indeed depended
upon the FcγR-mediated response in mice at least. To find out if this mechanism is relevant in
the clinic is the purpose of our study. To do so we analyze 14 studies investigating the
relationship between efficacies of mAb treatments in relation to polymorphisms of the FcγR.
Table 1 - Expression of some FcγR (adapted from Smith and Clatworthy, 2010)
Receptor
Activating
FcγRIIA
FcγRIIIA

NK cell
Lymphoid
Inhibitory
FcγRIIB




B cell
Plasma cell
Monocyte
Expression
Myeloid
DC
Platelet
Macrophage
Neutrophil












Granulocyte Basophil
Mast cell
The FcγRIIIa-158V/F polymorphism was most commonly evaluated in studies
comparing mAb therapy and FcR polymorphism (13 studies).
FcγRIIIa-158 is in the
membrane proximal domain receptor structure and is generally thought be located within the
IgG-binding site (Koene et al., 1997). The receptors on NK cells with a valine (V) amino acid
at this position are better at binding to IgG than those with a phenylalanine (F). Cells
extracted from heterozygotic patients (V/F) showed intermediate binding levels, an indication
of a gene-dosing effect. The clinical implications of this may mean that V-carriers have a
better ability to clear pathogens as their receptors will bind more IgG than F/F patients. On
the other hand, perhaps in vivo the V polymorphism enhances the binding of the receptor to
cytophilic IgG and therefore decreases availability of the receptors, preventing
receptor/immune complex interaction.
For similar reasons FcγRIIa-131 is the next most commonly studied polymorphism
(11 studies). The binding of FcγRIIa to murine IgG1 diminishes with the presence of a
histidine (H) at position 131 while binding is restored in receptors with an arginine at this
position (R) (Warmerdam et al., 1991). Although this study did not test human IgG1 or IgG3
which would give us a more accurate idea of what actually happens in vivo.
Lastly, we analyzed two studies that observe a polymorphism of the inhibitory
receptor FcγRIIb and effectiveness of mAb treatment. The genotype T/T at position 232 is
found more often in patients with systemic lupus erythematosus (SLE) than healthy
individuals (Kyogoku et al., 2002). SLE is an autoimmune disease where inflammation a key
problem. This has led to the hypothesis that the 232I genotype is contributing to proper
inhibitory signaling of the immune cells which may be impaired in T/T SLE patients.
Unfortunately only a few studies looked at these polymorphisms in patients with the
same type of cancer. The nature of the different kinds of cancers and modes of action of the
different mAbs can help us better understand the results of these varied studies.
1.2 Treatment of Cancers with mAbs
Targets of therapeutic mAbs can be on the surface of solid tumor cells or circulating
malignant cells. The targets can be part of the cancer cell’s membrane (i.e. transmembrane
receptors), receptor ligands (i.e. vascular growth factors), or even parts of the tumor stroma,
like extracellular matrix proteins.
1.2.1 mAbs with Targets on Solid Tumors
Trastuzumab (Herceptin ®; Genentech, Inc., South San Francisco, CA) is a
humanized mAb targeted to the extracellular domain of HER2/neu (See Table 2). HER2/neu
(c-erbB-2) is a member of the epidermal growth factor receptor (EGFR) family. It has been
found to be over-expressed in roughly 25% of breast cancers, inducing a cellular proliferation
and apoptosis resistance.
Table 2 - Unconjugated Monoclonal Antibodies used in Cancer Therapy
Generic Name (Trade Name)
Trastuzumab (Herceptin)
Rituximab
(Rituxin)
Cetuximab
(Erbitux)
Bevacizumab (Avastin)
Alemtuzumab (Campath-1H)
Panitumumab (ABX-EGF)
Origin
Humanized
Chimeric
Chimeric
Chimeric
Humanized
Human mAb
Isotype
Human IgG1
Human IgG1
Human IgG1
Human IgG1
Human IgG1
Human IgG2
Target
HER2/neu
CD20
EGFR
VEGF
CD52
EGFR
Indication
Breat Cancer
Lymphoma
Colorectal cancer (CRC)
CRC, Lung cancers
Chronic lymphocytic leukemia
Non-small cell lung, CRC
Year approved
by FDA
1998
1997
2004
2004
2001
2006
Cetuximab (Erbitux; ImClone Systems Inc, Branchburg, NJ) is a chimeric IgG1 mAb
targeted at EGFR (Table 2). It acts by preventing the ligand from binding to the receptor,
thwarting downstream proliferation signaling cascades. Studies have shown that cetuximab
interferes with the signal transduction but it can also illicit ADCC or CDC in vitro and hence
has multifaceted anti-tumor activity (Kang et al., 2007). Cetuximab is effective against
EGFR-over-expressing cancers either on its own or in combination with chemotherapeutic
drugs like irinotecan (Sobrero et al., 2008).
Panitumumab is also an anti-EGFR mAb but it has a higher affinity for EGFR than
cetuximab and hence is a stronger inhibitor. Comparatively it also has less side severe side
effects than cetuximab as it lacks murine sequences. In treatment of colon cancer both drugs
have similar efficacy (Yang et al., 1999).
1.2.2 mAbs with Lymphoma Targets
Rituximab is a CD20 mAb (Rituxan®; Genentech, Inc., South San Francisco, CA).
The mechanism behind this mAb mode of action is ADCC, CDC, and apoptosis as shown by
in vitro studies (Shan et al., 2000). Rituximab is effective against previously treated low-grade
B cell lymphomas (Bernstein et al., 1988; McLaughlin et al., 1998), low-grade or follicular
non-Hodgkin lymphoma with relapsed or primary refractory disease (Piro et al., 1999).
Alemtuzumab is a CD52-targeted mAb that can be used to treat chronic lymphocytic
leukemia (CLL). However it can cause higher toxicities than Rituximab and can cause serious
immunological complications, therefore it has been used less in the clinic (Christian and Lin,
2008).
As leukemia affects circulating cells instead of a stationary solid tumor mass this may
add an extra variable into our study.
1.2.3 mAbs with Targets in the Tumor Stroma
The tumor stroma can be a good place to look for targets for mAb cancer treatments as
tumor blood vessels, fibroblasts, inflammatory cells and matrix proteins found here differ
from those in normal tissue. However these mAb have not been evaluated yet in regards to
FcR polymorphism and are therefore not included in our study.
1.2.4 mAbs with Ligand Targets
Targeting ligands of receptors can be an effective means to fight tumors by blocking
tumor progressing signal transduction pathways from being activated. Bevacizumab is an
anti-VEGF (vascular endothelial growth factor) targeted mAb used as treatment of many solid
tumors (Willet et al., 2004). This type of mAbs will attach to the ligand of the receptor and
therefore is not physically attached to the tumor cells itself. This excludes the possibility of
ADCC or CDC from being the cause of tumor response or extended survival, therefore
ligand-targeted mAbs were excluded from our study.
1.3 Evaluating Treatment Outcomes
Clinical studies commonly consider three factors when evaluating effect of a cancer
therapy; tumor response, progression-free survival (PFS) and overall survival (OS). For
patients affected with solid tumors, the response in size of the tumor to a treatment is
evaluated in everyday practice as well as in clinical trials. It can be determined by two
different methods. Using a computed tomography (CT) scan, the diameter of the tumor can
be established. The World Health Organization (WHO) uses bidimentional readings from CT
scans (sum of the products of bidimentional readings of each tumor) to determine response,
while the Response Evaluation Criteria in Solid Tumors (RECIST), calls for simplified
unidimentional CT readings (sum of the longest diameter of each tumor). Both methods yield
comparable results in determining tumor response (Park et al., 2003).
There is a classification system based on degree of tumor response. Complete response
(CR) is defined identically by both WHO and RECIST: disappearance of tumor(s) confirmed
at 4 weeks. Partial response (PR) is defined by both as a reduction in tumor size of at least
65% volume-wise, confirmed at 4 weeks. Stable disease (SD) is defined as the observation of
neither PR nor PD. However RECIST is less stringent then WHO on progressive disease (PD)
classification: RECIST requires a tumor volume increase of at least 73% in verses WHO
which requires only a 40% increase (Padhani and Ollivier, 2001). RECIST chose a higher
threshold as to minimize the effect of enlarging small tumors.
A common set of definitions for response concerning non-Hodgkin’s lymphomas
comes from the Cheson guidelines: complete response defined as at least 75% reduction in
sum of the products of the longest diameters of the tumors (SPD) (Cheson et al., 1999).
Partial response is defined as at least 50% decrease in SPD. Stable Disease defines as less
than a PR response but not progressive disease (PD), while PD is characterized as at least a
50% increase in SPD or the appearance of new lesions.
Tumor shrinkage is a traditional factor evaluated in phase II clinical trials because it is
relatively quick way to assess if a drug has anti-tumor properties. In the past a response to a
drug tended to reflect increased patient survival (PFS and OS) which is usually evaluated in
phase III. This conjecture has held true for cytotoxic drugs. However recently it has been
pointed out that a number of effective molecularly targeted cancer drugs have shown marginal
impact on response rate but subsequently showed strong positive results concerning PFS and
OS (Dhani et al., 2009). These studies indicate that tumor stabilization may be an important
indicator of an effective treatment resulting in clinical benefit, more so than observing a CR
or PR.
OS is a clinical end-point of most importance and is considered the “gold-standard”
measurement for testing new cancer drugs (Dhani et al., 2009). However this measurement is
subject to confounding factors such as effects of crossover designs or the use of salvage
therapies. Only a couple of the FcR polymorphism studies have been able to look at this
parameter.
PFS is a middle of the road end-point. It avoids the confounding effects of OS like
crossovers or subsequent treatments. The relevancy of PFS is determined by the intervals of
follow-ups. Although PFS is under the influence of potential assessment and investigator bias
if the trail is not blinded.
Our investigation focused on the studies evaluating the relationship between FcγR
polymorphisms and efficacy of non-conjugated, cell-targeted mAb therapies for solid tumors
and hematological cancers. We take into account if the studies are retrospective or
prospective, cohort size and previous patient treatments, how polymorphisms were detected,
frequency of polymorphism, means of measuring response, response itself, timing of
evaluations and progression-free survival (PFS). Tumor response and PFS were the primary
endpoints of our study. Tumor shrinkage was as it is more a reflection of ADCC or CDC
being activated than PFS or OS. We chose to look at PFS as well as it is a good indicator of
clinical benefit and OS was simply not available in most cases. Knowing if the FcγR
polymorphisms are a biomarker for outcome of mAb treatment would be a great help in
selectively treating only the patients who would most likely benefit. This would assist in
avoiding chemotherapy toxicity and reducing treatment costs.
2. Results
Seeing as ADCC is responsible for part of the efficacy of some mAb treatment,
researchers have hypothesized that polymorphisms of the FcR gene that alter affinity of the
receptor for the mAb can influence the ADCC response to a tumor. This may alter the PFS of
patient. Ultimately if the FcR polymorphisms can be used as a biomarker for response to mAb
treatments, this would help in choosing to only treat patients that would most likely benefit
from the mAb. This would assist in avoiding chemotherapy toxicity and reducing treatment
costs.
Most studies on the association of FcRs with mAb efficacy have so far focused on two
polymorphisms: (1) FcγRIIa (CD 32) polymorphism at position 131, histidine (H)/ arginine
(R) (van Sorge et al., 2003) and (2) FcγRIIIa (CD16) polymorphism at position 158, valine
(V)/phenylalanine (F). As FcRIIa-131H and FcγRIIIa-158V have the higher binding affinities
to IgG1 than the R or F variants respectively. Therefore it is hypothesized that patients who
are carriers for 131H and/or 158V have the favored genotypes for initiating the anti-tumor
ADCC mechanism (Parren et al., 1992; Koene et al., 1997; Strome et al., 2007). Furthermore
we were expecting to see a gene-dosing effect where heterozygotes of the favored allele
would have an intermediate response/PFS while the homozygotes, H/H or V/V, would have
the best outcomes.
2.1 Population frequencies of FcγR polymorphisms
Each study stated the number of patients with each genotype (Table 3). This allows
confirmation that there is not linkage between the polymorphism and the disease. Only the
Musolino study found a population frequency out of Hardy-Weinberg equilibrium. They
didn’t compare this genotype frequency to that of a control group so it cannot be certain that
the genotype is not linked the disease.
Table 3 – Frequency of genotypes of various FcγR polymorphisms. Yellow indicates
populations not in Hardy-Weinberg equilibrium
Disease, Study
Follicular Lymphoma, Weng 2003
B-cell Lymphoma, Zhang 2010
B-cell Lymphoma, Mitrovic 2007
B-cell Lymphoma, Kim 2006
T-NHL, Zhang 2010
CLL, Dornan 2010
CLL, Lin 2005
CLL, Farag 2004
CRC, Bibeau 2009
CRC, Zhang 2007
CRC, Paez 2010
Breast Cancer, Musolino 2010
Follicular Lymphoma, Cartron 2002
Frequency of
Genotypes
(Percent)
FcgRIIIa-158
V/V V/F F/F
15
46
39
32
53
15
28
55
17
5
48
47
21
71
7
10
50
40
12
30
58
20
40
40
15
63
22
14
40
46
15
39
45
20
48
32
20
45
35
CRC, Pander 2010
FcRIIIa-818
A/C or
A/A
C/C
47
53
CRC, Pander 2010
FcRIIa-535
A/G or
A/A
G/G
27
73
Disease, Study
Follicular Lymphoma, Weng 2003
B-cell Lymphoma, Mitrovic 2007
B-cell Lymphoma, Kim 2006
CLL, Dornan 2010
CLL, Lin 2005
CLL, Farag 2004
CRC, Bibeau 2009
CRC, Zhang 2007
CRC, Paez 2010
Breast Cancer, Musolino 2010
Follicular Lymphoma, Cartron 2002
Frequency of
Genotypes
(Percent)
FcRIIa-131
H/H H/R R/R
23
49
28
40
46
14
56
37
7
26
55
19
18
67
15
20
57
23
28
44
28
26
48
26
26
52
22
18.5
63 18.5
29
51
20
FcRIIb-232
Breast Cancer, Musolino 2010
I/I
81
2.2 FcγRIIa-131 polymorphisms and mAb efficacy
The H allele of the FcγRIIa-131 locus confers a higher binding affinity of the receptor
for IgG. Therefore it was expected that H-carriers or H/H patients would have better
responses and longer PFS than the other patients. We found that there was only one study out
I/T T/T
11
8
of 10 studies that found a significant relationship between genotype and response (Table 4).
The H/H patients showed the better response in that study which agrees with our hypothesis.
Furthermore there were two studies which found a non-significant trend for H/H or H-carrier
patients with better responses. However there were also two studies which found that Rcarriers have a non-significant trend towards better response. Interesting these studies were
both looking at colorectal cancer patients treated with cetuximab plus chemotherapy. Perhaps
these insignificant trends simply show up as the cohorts are too small (See Supplemental Data
Table). Overall this evidence makes a very weak case for the FcγRIIa-131 polymorphism
being linked to response in general, but there is a significant relationship for follicular
lymphoma treated with Rituximab.
Eight studies examined the correlation between the FcγRIIa-131 polymorphism and
length of PFS. Three of them found that patients with the H/H genotype or H-carriers have
significantly longer average PFS than the other patients (Table 4). These three studies are
each looking at different diseases, each treated with a different drug. This shows that while
significant connections between genotype and response as well as PFS is rare (only one study
out of 10 found this), it is more common to find a good clinical benefit associated with the
genotype and simultaneously not find tumor response. Follicular lymphoma treated with
rituximab appears to have significant association with response and PFS.
2.3 FcγRIIIa-158 polymorphisms and mAb efficacy
Concerning the FcγRIIIa-158 polymorphism the V-carriers were expected to have
better response than other patients, as this allele makes the receptor have a higher affinity for
the IgG. We found that the V/V genotype conferred a better response over the F-carriers in 4
of the 12 studies, and one study showed V-carriers had the advantage (Table 4). No study
found F/F or F-carriers to hold an advantage for response. Interestingly 4 of the 5 studies
which found the V-carriers to have better responses were performed in lymphoma patients (Bcell and follicular) treated with rituximab. In general it appears that there is a significant link
between the V-genotype and response for lymphoma and breast cancer patients.
Looking at non-significant trends, three of the 12 studies show that F-carriers have
better responses than the other patients. This is unexpected and counter-intuitive as it has been
shown that the F-allele has a lower affinity for the mAb. Two of these studies were on
patients with colorectal cancer (CRC).
Table 4 – Response and PFS According to Genotype of FcRs.
FcRIIa-131
Response
H/H
H/R
PFS
Disease, Study
Treatment
Follicular Lymphoma, Weng 2003
CRC, Zhang 2007
Rituximab
Cetuximab + I
H/H advantage
No Association #
R/R
H/H advantage
H-carriers advantage
H/H
H/R
R/R
Breast Cancer, Musolino 2010
B-cell Lymphoma, Mitrovic 2007
Trastuzumab + T
Rituximab + CHOP
No Association +
No Association
H/H advantage over R/R
No Association
B-cell Lymphoma, Kim 2006
CRC, Bibeau 2009
Rituximab + CHOP
Cetuximab
No Association *
No Association
No Association
No Association
CRC, Paez 2010
CLL, Dornan 2010
Cetuximab/Pan ~I
Rituximab + FC
No Association #
No Association
No Association
No Association
CLL, Lin 2005
CLL, Farag 2004
Alemtuzumab
Rituximab
No Association
No Association
N/A
N/A
FcgRIIIa-158
Response
V/V
V/F
PFS
Disease, Study
Treatment
Follicular Lymphoma, Cartron 2002
Follicular Lymphoma, Weng 2003
Rituximab
Rituximab
V/V advantage
V/V advantage
F/F
No Association
V/V advantage
V/V
V/F
F/F
Breast Cancer, Musolino 2010
B-cell Lymphoma, Kim 2006
B-cell Lymphoma & T-NHL, Zhang 2010
CRC, Bibeau 2009
CRC, Zhang 2007
B-cell Lymphoma, Mitrovic 2007
CLL, Dornan 2010
Trastuzumab + T
Rituximab + CHOP
Rituximab + CHOP
Cetuximab + I
Cetuximab
Rituximab + CHOP
Rituximab + FC
V/V advantage
V/V advantage
V-carriers advantage
No Association
No Association †
No Association
No Association
V/V advantage
No Association
No Association ‡
V/V advantage
F-carriers advantage
No Association
No Association
CRC, Paez 2010
CLL, Lin 2005
CLL, Farag 2004
Cetuximab/Pan ~I
Alemtuzumab
Rituximab
No Association †
No Association
No Association †
No Association
N/A
N/A
FcRIIb-232
Response
Disease, Study
Treatment
Breast Cancer, Musolino 2010
Follicular Lymphoma, Weng 2009
Thrastuzumab + T
Rituximab
I/I
I/T
PFS
T/T
No Association º
No Association
I/I
I/T
T/T
No Association
N/A
FcRIIIa-818
Response
Disease, Study
Treatment
CRC, Pander 2010
Cetuximab + COB
A/A
PFS
A/C or C/C
N/A
A/A
A/C or C/C
A/A advantage
FcRIIa-535
Response
Disease, Study
Treatment
CRC, Pander 2010
Cetuximab + COB
A/A
N/A
A/G or G/G
PFS
A/A
A/G or G/G
No Association
Legend: + I = irinotecan, ~ I = some patients received irinotecan, Pan = 12% of patients received Panitumumab
instead, T = Taxane, FC = Fludarabine + Cyclophosphamide, † F-Carriers trend advantage (Non-Sig), ‡ V-
Carriers trend advantage (Non-Sig), * H-Carriers trend advantage (Non-Sig), # R-Carriers trend advantage (NonSig), + H/H advantage (Non-Sig), N/A - data not available, COB = Capecitabine, Oxaliplatin and Bevacizumab,
º I/I adv (not sig.)
In conclusion the V-allele is a good indicator of response for lymphoma and breast cancer
patients, while potentially the F-allele is linked to better response in CRC patients.
Of 5 the studies that found the V/V or V-carrier patients to be significantly better
responders, only 2 of them found that these patients also had a longer PFS. Interestingly these
2 studies were evaluating responses from different mAb, Rituximab and Trastuzumab,
illustrating that this is not a drug-specific effect. Furthermore these two studies were looking
at patients with different diseases, follicular lymphoma and breast cancer, implying this effect
is also not specific to cancer type. There were 2 studies which did not find a correlation of
genotype with response but did find a correlation with PFS. One found that the V/V carriers
had the advantage and the other found that the F-carriers did. Strangely both studies were on
CRC patients. In conclusion there is some evidence that the FcγRIIIa-158V/V genotype
corresponds with better PFS for patients with follicular lymphoma or breast cancer. There is
inconclusive evidence for linkage of genotype with the PFS of patients with CRC.
2.4 FcγRIIb-232 polymorphisms and mAb efficacy
Two studies evaluated a polymorphism of the inhibitory receptor FcγRIIb. The T allele
may weaken the affinity of the receptor for IgG. As it is an inhibitory receptor we thought the
T allele would enhance ADCC/CDC and result in a better response/PFS. Both Follicular
lymphoma patients and breast cancer patients showed responses to rituximab and trastuzumab
respectively which did not correlate their FcγRIIb-232 genotype (Table 4). In the Musolino
study (2008) there is evidence that the T-carriers are less likely to respond to the trastuzumab
treatment than I/I patients, but it was not significant (see Supplemental Data).
Furthermore PFS was not significantly associated with any genotype in both studies
(Weng study could not evaluate PFS for T/T patients). It appears that this receptor and/or
polymorphism do not play a significant role in the efficacy of mAb treatments.
2.5 FcγRIIIa-818 and FcγRIIa-535 polymorphisms and mAb efficacy
A recent randomized study performed by Pander and colleagues examined the
FcγRIIa-535 and FcγRIIIa-818 polymorphisms in KRAS wildtype mCRC patients (Pander et
al., 2010). Previously untreated patients were administered chemotherapy (capecitabine +
oxaliplatin) and bevacizumab with the addition of cetuximab. Response was not evaluated in
this study.
The FcγRIIIa-818 C-carriers were found to be associated with decreased PFS (Table
4). Most important was the finding that the FcγRIIIa-818 polymorphisms were not associated
with PFS in patients not given cetuximab. This highlights that the polymorphism is not
causing a non-drug related effect on clinical outcome. FcγRIIa-A535G polymorphism was
found to not be associated with PFS. In conclusion the FcγRIIIa-818 A/A genotype appears to
be linked with increase PFS for CRC patients.
3. Discussion
We set out to prove or disprove if the higher affinity of certain FcγR polymorphisms
for IgG correlate with better response and longer PFS of cancer patients treated with
therapeutic mAb.
Frequency of FcγR Genotypes in Populations
In general the frequencies of genotypes in the populations appear to have normal
distributions (Table 3). An exception is the Kim study which used Korean patients and seems
to have a population biased towards certain genotypes which could skew their correlation
results. For this reason the Kim study results which show a significant correlation of the
FcγRIIIa-15V/V genotype with response but not with PFS may be the result of this particular
population. Although the Zhang study used patients of a different population with same
disease, treated with the same mAb and found similar results. On the other hand there is the
Mitrovic study which used Caucasian patients and found no correlation with either response
or PFS, a plausible explanation for the difference in results with the Kim study.
Weather the difference between populations really is the cause of the differing results
is unknown, but perhaps the low number of patients in certain genotypes in the Kim study is
causing results to be insignificant which may become significant in a larger population or vice
versa.
FcγRIIIa-158 Tumor response doesn’t necessarily correlate with
increased Clinical Benefit
Response and PFS
Concerning the FcγRIIIa-158 polymorphism, 5 studies of 12 studies found that the
V/V genotype (the higher affinity allele) or V-carriers had better response over the F-carriers.
Of these 5 the studies, only 2 found that these patients also had a longer PFS. Perhaps the
disparity between response and PFS in three of the studies occurs as the drug affects tumor
size, but the side-effects it causes are the trumping factor and limit PFS.
V/V and V-carrier Lymphoma and Breast Cancer Patients Display Better
Responses
Importantly, 4 of the 5 studies which found the V-carriers to have better responses
were performed in lymphoma patients (B-cell and follicular) treated with rituximab. In
general it appears that there is a significant link between the V-genotype and response for
lymphoma and breast cancer patients.
Conflicting results concerning Cetuximab-Treated mCRC
There were 2 studies which did not find FcγRIIIa-158 genotype correlating with
response but did find a correlation with PFS. One of them found that the V/V patients had
longer PFS while the other found that the F-carriers did. Both of these studies were treating
CRC patients with cetuximab. A major difference between the two was that the Bibeau study
used cetuximab plus irinotecan as treatment (V/V patients advantage) and the Zhang study
(2007) used single-agent cetuximab as treatment (F-carriers advantage). Perhaps this variable
causes the difference, but it could also be that the Zhang study simply had too small a cohort
(39 patients) get a clear result, while the Bibeau study was larger (69 patients) and perhaps is
thus more reliable. Furthermore there was a third study (Paez, 2010) which also looked at
CRC patients treated with Cetuximab, but no correlation with response or PFS was found.
This study by far had the largest patient cohort, 104 patients, and therefore is probably the
more definitive study out there. In conclusion it appears that there is not agreement on the link
between FcγRIIIa-158 genotype and response/PFS concerning CRC.
Rarely Does Better Response Also Correlate with Better PFS
Of 5 the studies that found the V/V or V-carrier patients to be significantly better
responders, only 2 of them found that these patients also had a longer PFS. Interestingly these
2 studies were evaluating responses from different mAb, Rituximab and Trastuzumab,
illustrating that this is not a drug-specific effect. Furthermore these two studies were looking
at patients with different diseases, follicular lymphoma and breast cancer, implying this effect
is not specific to cancer type.
In conclusion there is some evidence that the FcγRIIIa-158V/V genotype corresponds
with better PFS for patients with follicular lymphoma or breast cancer. Our study found that
there is not convincing evidence for better response being linked to longer PFS in general (10
of the 12 studies). A plausible explanation may be that the patients that had significantly
longer PFS was because they had stable disease (rather than PR or CR), and this may be an
overlooked mechanism of improving clinical benefit. For example, some studies have pointed
out that a non-response does not always signify a shorter PFS or OS. In a retrospective study
by Grothey and colleagues (2008) it was found that the classifications “responder” or “non-
responder” put upon mCRC patients after bevacizumab + IFL treatment did not correspond
with those who had longer PFS and OS. This could be why we find little correlation with
response and those patients who had longer PFS.
Indeed this is the case in the Zhang study (2007). Concerning their FcγRIIIa-158
polymorphism results, 71% of F/F patients showed PR or SD and 29% PD, while
heterozygote F/V patients showed 71% PR or SD and 29% PD, while the V/V homozygous
patients showed 20% PR or SD and 80% PD. Seeing as F-carriers had significantly longer
PFS than V/V patients it can be said that PR + stable disease is an indicator of clinical benefit.
The stable disease classification could be seen as a positive indicator of clinical benefit, a
predictive condition that is currently not given enough credit.
High Threshold for ADCC-induction?
Another question lingering in the wake of these results is why the studies which found
the V/V genotype at an advantage concerning response, did not find a significant intermediate
response for V/F patients. This would be expected if the hypothesis that the V-allele is
advantageous because of its heightened affinity, then wouldn’t we expect to see a gene-dose
effect, instead of the clear advantage of the V homozygotes. Perhaps there is a threshold of
activated receptors that needs to be reached to have a positive effect and this threshold is
simply not reached in heterozygotes.
In general it appears that there is a significant link between the V-genotype and
response for lymphoma and breast cancer patients. Furthermore there is some evidence that
the FcγRIIIa-158V/V genotype corresponds with better PFS for patients with follicular
lymphoma (FL) or breast cancer. There is inconclusive evidence for linkage of genotype with
the PFS of patients with CRC. Perhaps this genotype is useful only for evaluating treatment
options of patients with FL or breast cancer.
FcγRIIa-131
Polymorphism Usually does not Correlate with Response
Concerning the FcγRIIa-131 polymorphism, there was one study out of 10 studies that
found a relationship between genotype and response. H/H patients showed better response in
that study which agrees well with the fact that the H-allele confers higher affinity of the
receptor for the mAb. However it is not so surprising that less studies found correlation with
this polymorphism those of the FcγRIIIa-158 polymorphism, as the affinity of the FcγRIIa
receptor is strong for murine IgG1 and human IgG2, which can be quite different from the
human IgG1 backbone which most mAb tested here are.
PFS
3 of the 8 studies looked at the polymorphism and PFS found correlation, H/H or Hcarriers having the advantage. These three studies are each looking at different diseases, each
treated with a different drug, which is quite remarkable, implying again that this phenomenon
is not drug- or disease-specific.
Stable Disease May Be a Better Indicator of Longer PFS than CR/PR
A number of effective molecularly targeted cancer drugs have shown marginal impact
on response rate then subsequently showed strong positive results concerning PFS and OS
(Dhani et al., 2009). These studies indicate that tumor stabilization may be an important
indicator of an effective treatment resulting in clinical benefit, as we proposed with the
FcγRIIIa-158 polymorphism.
There is evidence for the FcγRIIa-131 polymorphism acting similarly. The Zhang
study (2007) shows that the 131R polymorphism is not significantly associated with response.
However of the H/H patients 0% had a PR, 78% SD and 22% PD, while H/R patients showed
6% PR, 71% SD and 24% PD, and R/R patients showed 14% PR, 0% SD, and 86% PD. If
one only takes into account percentage of PR, it shows the R-carriers have an (not significant)
advantage response-wise, which is what Zhang notes, but if one looks at the PR + SD it is the
H-carriers who have a great advantage, nearly five times as high percentage over the R/R
patients. This correlates with the significantly longer PFS of the H-carriers. It appears that the
R/R genotype certainly points to a poor prognosis as they have shorter median PFS and higher
PD percentages.
As Zhang used Cetuximab mono-therapeutically, I think the data from this study a
more solid result than those from studies using combinational therapies which may be
confounding results. The Zhang study makes a strong case that cetuximab can stabilize a
tumor can extend PFS.
Confounding Effects of Using Combination Treatments
The Dornan study (2010) showed no influence of genotype over response or PFS
concerning both FcRIIa-131 and FcγRIIIa-158 polymorphisms. This could be due to the
combination treatment administered to patients, FC + rituximab. They do point out that the
difference in PFS is significant between heterozygous patients for both FcRIIa-131 and
FcγRIIIa-158 treated with R-FC compared to the heterozygous patients treated only with FC.
This implies this second part of the therapy (FC) may have confounding effects on the
interpretation of the results. This could also be a factor of many of the other studies seeing as
combinational therapies are common practice, but can add in an extra variable into the
equation. Furthermore the Dornan study also had a relatively low occurrence of V/V patients
in their study and perhaps evaluating more V/V patient would change the significance.
FcγRIIb-232 Polymorphism may not Influence mAb Efficacy
The two studies examining the FcγRIIB-232 polymorphism found no association of
genotype with response of PFS. This may be because it is an inhibitory receptor, and by
having a polymorphism that make the receptor bind less well to the mAb apparently does not
provide an advantage, such as indirectly promoting inflammation by its prevention of
activating the inhibitory signaling pathway.
FcγRIIIa-818A/A Cetuximab-treated CRC Patients More Likely to Have
Longer PFS
The polymorphisms FcγRIIa-535 and FcγRIIIa-818 were looked at exclusively by one
study on CRC patients. Only FcγRIIIa-818A/A patients were shown to have a significantly
longer PFS than the other patients. Seeing as the studies concerning the FcγRIIIa-158
polymorphism and CRC had highly conflicting results, the Pander experiment should also be
repeated with another cohort, as perhaps CRC is a very variable disease concerning response,
and obviously the results from one experiment are not decisive.
Interestingly the Pander study made sure that their patient cohort was genotyped to be
KRAS-wildtype. Perhaps this is a variable future CRC studies should also take into account.
Response is a Reliable Read-out?
Using response in tumor size as an end-point may be a difficult reliable read-out, as
measurements of tumor diameters can fall to error and observer variation in determining
lesion boundaries is high (Padhani and Ollivier, 2001). This can lead to mis-classification of
disease stage and confound results, and could be why there was a lack of significant effects
found in many of the studies. PFS would also include the necessary volume determination
procedure and would be subject to such error. Due to this perhaps OS is a better indicator of
clinical benefit as it is a measurement not given to such inaccuracy. Overall, there needs to be
more studies performed which evaluate larger numbers of patients, are prospective and take
into account OS.
Why Does FcγRIIIa-158 Genotype Correlate with Response in Lymphoma
Patients but not Leukemia?
CLL cells have lower expression of CD20, the target for rituximab, than follicular or
B-cell lymphomas (Dornan et al., 2010). This could explain why 4 of the 5 lymphoma studies
we reviewed state a relationship with the FcR polymorphisms and tumor response to
rituximab while none of the 3 studies on CLL found an association. If the rituximab target is
expressed less in CLL then hypothetically ADCC would probably occur less and hence an
imperceptible difference in treatment efficacy amongst the FcR genotypes of CLL patients
would result. Furthermore, it has been proposed that an over-expression of CD55 or CD59
can cause inhibition of CDC (Bannerji et al., 2003). Perhaps this is the case for CLL and
explains why the 3 studies on this disease and rituximab show no correlation with the
polymorphisms.
Alternatively it may be possible that ADCC is better at eliminating neoplastic B-cells
in lymph nodes (Lymphoma) than when they’re in the blood and bone marrow (CLL) (Farag
et al., 2004). This can also cause the discrepancy between results over these two disorders.
Rituximab and alemtuzumab probably work through non-ADCC/CDC mechanisms in
patients with CLL.
It has been postulated that efficacy of the CDC pathway in tumor degeneration may be
dependent upon number or density of antigen sites on a given tumor cell’s surface (Adams
and Weiner, 2005). This idea has been further supported by an in vitro study which shows
CDC activation is correlated with expression levels of CD20 (Golay et al., 2001).
Furthermore the CDC pathway can help to contribute to ADCC because upon release of C3a
and C5a, NK and other effector cells can be recruited to the tumor and promote ADCC
(Gelderman et al., 2004). We hypothesize that because CLL cells have lower levels of CD20
they are not affected by ADCC/CDC and therefore no correlation with the FcR polymorphism
are found. For CLL treatment, target-disrupting effects are therefore probably the main mode
of action.
4. Conclusion
In conclusion it appears that there is not a clear cut answer for relationship between
FcγR polymorphisms and efficacy of mAb treatment. Perhaps due to the many different kinds
of combinational therapy that are used, a clear cut answer many never be found. Each study
was slightly different concerning patient cohort or exact treatment. However the trend seems
to be that FcγRIIIa-158V/V genotype does improve response to treatment and can provide a
longer PFS for lymphoma and breast cancer patients. For the FcγRIIa-131 polymorphism, it
appears H-carriers can have longer PFS than other patients. mAb treatments do not
correspond with FcR polymorphisms in patients with follicular lymphoma. Furthermore we
find that the “stable disease” classification can be linked with longer PFS and could
potentially be considered a good prognostic indicator for clinical benefit.
Supplemental Data
Table of Experimental Designs
Disease, Study
Follicular Lymphoma,
Cartron 2002
Previous Treatment
Treatment
Dose
72 patients chemotherapy
(10 bone marrow
transplants)
Rituximab
4 Weekly 375 mg/m2
Rituximab
4 Weekly 375 mg/m2
-
Thrastuzumab + T
4 mg/kg, then 2 mg/kg
-
Rituximab + CHOP
6 Cycles 375 mg/m2
Failed 1 irinotecan
treatment, majority also
oxalipatin
Failed 2 chemotherapy
regimens
Rituximab + CHOP
21-day cycle (6-8 cycles)
Cetuximab + I
Standard + I
Cetuximab
Standard
Rituximab + CHOP
3 Cycles (plus 1-5 more) 375 mg/m2
Rituximab + FC
N/A
CRC, Paez 2010
Previous Treatment
unnamed
Failed 1 chelotherapy
regimen
Cetuximab/Pan ~I
N/A
CLL, Lin 2005
~3 treatments
Alemtuzumab
week 1: 3-30 mg, then thrice every week (12 weeks)
CLL, Farag 2004
-
Rituximab
4 Weekly 375 mg/m2
CRC, Pander 2010
Follicular Lymphoma,
Weng 2009
-
Cetuximab + COB
400 mg/m2 , then 250 mg/m2
81 patients relapsed
Rituximab
4 Weekly 375 mg/m2
Follicular Lymphoma,
Weng 2003
Breast Cancer,
Musolino 2010
B-cell Lymphoma, Kim
2006
B-cell Lymphoma & TNHL, Zhang 2010
CRC, Bibeau 2009
CRC, Zhang 2007
B-cell Lymphoma,
Mitrovic 2007
CLL, Dornan 2010
Disease, Study
Follicular Lymphoma, Cartron
2002
Follicular Lymphoma, Weng 2003
Breast Cancer, Musolino 2010
B-cell Lymphoma, Kim 2006
B-cell Lymphoma & T-NHL,
Zhang 2010
Number DNA
of
Tissue
Patients Origin
Genotyping Method
Evalutation
Criteria
Evaluation TimePoints after end of Treat
49 BM/PB
RD
Cheson
day 50 or 78, 1 year
87 T/PB
RD+DS
Cheson
month 1/3, then every 3 months
54 PB
rtPCR +/or DS
RECIST
N/A
RD
Cheson
2/3 cycle, month 1, then every 4 months
113 BM/PB
48 PB
AS-PCR
Cheson
every 2 cycles
CRC, Bibeau 2009
69 T/N
AS-PCR or DS
RECIST
every 2-3 months
CRC, Zhang 2007
39 PB
RD or AS-PCR
Own Criteria
every 6 weeks
B-cell Lymphoma, Mitrovic 2007
58 N/A
PCR+RD
Cheson
cycle 3/4, then at end of treatment
CLL, Dornan 2010
210 PB
RT-PCR+RD
N/A
N/A
CRC, Paez 2010
104 PB
48.48 Dynamic Array
RECIST
every 2-3 months
CLL, Lin 2005
36 PB
PCR+RD
Cheson/NCI 96
Weekly
CLL, Farag 2004
30 PB
PCR+RD
Cheson
month 2
CRC, Pander 2010
127 PB
AS-Probes + RT-PCR
RECIST
every 3 cycles
Follicular Lymphoma, Weng 2009
101 T/PB
AS-Probes
Cheson
month 1/3, then every 3 months
Legend :
BM/PB
PCR+RD
T
DS
AS-PCR
Bone Marrow or Peripheral Blood
PCR + Allele-Specific Restrection Enzyme Digest
Tumor
Direct Sequencing
Multiplex allele-specific PCR
rt
N
reverse transcription of cDNA
no previous treatment
normal tissue
FcγRIIIa-158
Weng Study (2003)
The FcγRIIIa-158 V/V genotype was determined to be a predictive factor for response at 1 to
3 months, 6, 9 and 12 months. About 45% of patients with the V/V genotype had PFS at 2
years post-treatment, while 12% of heterozygotic patients had PFS, and 16% for the F/F
patients.
Zhang Study (2010)
A retrospective study by Zhang and colleagues (2010) analyzed patients with B-cell
lymphoma (34 patients) and T cell non-hodgkin lymphoma (14 patients). All patients received
rituximab plus CHOP (21-day cycle for 6-8 cycles). Patients who reached neither PR or
relapsed received a salvage treatment of etoposide + cisplatin + cytarabine +
methylprednisolone (ESHAP)/mitoxantrone + ifosfamide + etoposide (MINE) for 2-4 courses
until PR was reached. The rituximab + CHOP was effective (PR + CR) in 82% of patients
with the V/V genotype. 83% of heterozygous (V/F) patients showed a response to treatment,
while patients homozygous F had only 60% had a good response rate. While the researchers
state they found no statistically significantly differences amongst the genotypes concerning
PFS or OS, the PFS at 1 year of V/V patients was 73%, heterozygotes (V/F) 69% and F/F
homozygotes 20%. The F/F patients appear to be at the disadvantage. Only response rate was
deemed by the researchers as an independent prognostic factor of OS, not genotype.
Farag Study
In a study by Farag and colleagues (2004) the efficacy of rituximab on CLL patients was
evaluated considering the FcγRIIIa-158 polymorphism. 33% of V/V patients responded
positively, 42% of V/F and 50% of F/F patients. The trend implies a benefit for the F-carriers
but no significant association with response was found.
Bibeau Study
Patients homozygous 158V had 6.9 months PFS compared to the F-carriers who had 3.2
months.When taking into account the FcγRIIa and FcγRIIIa polymorphisms together, no
significant difference in response was observed between 131H and/or 158V homozygotes
versus the others. However 131H and/or 158V homozygotic patients did have significantly
longer PFS compared to the others (5.5 months vs. 3 months). The results of the Bibeau study
showed that combined the FcγRIIa-131H/H and/or FcγRIIIa-158V/V polymorphisms are
prognostic factors for PFS in mCRC patients treated with cetuximab plus irinotecan.
However they are not influential concerning tumor responses.
Zhang Study (2007)
Concerning the FcγRIIIa-158V/F polymorphism results from the Zhang study (2007), 14% of
the F/F patients showed PR, 57% SD and 29% PD, while heterozygote F/V patients showed
0% PR, 71% SD, and 29% PD, while the V/V homozygous patients showed 0% PR, 20% SD
and 80% PD. This trend shows that the F-carriers have a much better response to cetuximab
than the patients homozygous for 158V, but it is not a significant association.
Concerning PFS the Zhang study found that patients who were homozygous for
FcγRIIIa-158F had a median PFS of 2.3 months while heterozygous patients had a PFS of 2.4
and the homozygous 158V patients had a PFS of 1.1 months. Combining both FcRIIa and
FcγRIIIa genotypes yielded highly statistically significant relationship between the
polymorphisms and PFS. Patients who are carriers of both H and F allele(s) have a median
PFS of 3.7 months while R/R or V/V patients have a PFS of 1.1 months on average.
Paez Study
While it is not significant, there is a trend of benefit in response for the F-carriers (54% of
V/V patients showed PR or SD, 60% of V/F and 72% of F/F patients).
Cartron Study
PFS survival was evaluated 3 years after treatment. 56% of V/V patients had PFS and 35% of
F-carriers, not a significant difference.
FcγRIIa-131
Weng Study (2003)
An advantage of the H/H patients was also found when observing PFS: 37% of H/H patients
had PFS as 2 years post treatments, while only 13% of H/R patients and 19% of R/R patients.
The H/H PFS was significantly longer than that of the other genotypes. These results were
confirmed again in a more recent study by the same investigators expanding the same patient
pool from 87 to 101 patients (Weng and Levy, 2009). Again the H/H patients had better
response and better PFS than the R-carriers.
Mitrovic Study
In a study by Mitrovic and colleagues (2007) diffuse large b-cell lymphoma (DLBCL)
patients were evaluated for their response to treatment of rituximab plus standard CHOP
(cyclophosphamide, doxorubicin, vincristine, and prednisolone). Patients who responded to
the treatment were continued on it for another 1-5 cycles, while patients who did not respond
were either given radiation treatment and/or second-line chemotherapy followed by peripheral
blood stem cell transplantation.
Kim Study
In a retrospective study of Korean DLBCL patients Kim and colleagues (2006) investigated
response to first-line R-CHOP therapy in relation to their FcγR polymorphisms. 76% of these
patients received only the R-CHOP treatment while the remaining 33% of patients were
subsequently treated with radiation. A median of 6 cycles of R-CHOP had been administered
to patients, rituximab given at the standard dose. Event free survival (EFS) is defined as time
from day 1 of the first R-CHOP cycle until treatment failure, which includes DP, recurrence
or death from any cause. The Kim study (2006) found there was a non-significant trend of
better response towards patients with the H/H genotype (ORR of 95% compared to 92% of
H/R and 75% of the R/R patients).
Dornan Study
This retrospective study revealed a slight trend towards the H/H genotype of being more
beneficial for median PFS (31.8 months for H/H, 27.3 for H/R and 26.7 for R/R patients).
Zhang Study (2007)
These patients were part of a phase II open-label multicenter study. Treatment was continued
until disease progression or the occurrence of toxicity. An objective response was defined as
reduction of at least 50% of tumor size using CT. Objective responses were confirmed 4
weeks after the initial detection. Tumor progression was defined as an increase of at least 25%
of tumor area or the appearance of new lesions. Response was also measured retrospectively
in an independent blinded assessment. The Zhang study shows a trend for R-carriers having
an advantage can be found considering PR alone. Concerning PFS, the patients that were
131H homozygous had a PFS of 2.4 months, while heterozygotic patients had a median PFS
of 3.7 months, and the 131R homozygous patients had a PFS of 1.1 months. This would
indicate that the H-carriers have the advantage concerning PFS.
Paez Study
When considering the FcγRIIa-131 polymorphism they found 54% of H/H patients had PR or
SD, 64% of H/R patients and 77% of R/R. This implies a trend of R-carriers to have better
response to this treatment. Perhaps with a larger cohort this would be significant.
Musolino Study
This study comprised of patients with HER2/neu-positive metastatic breast cancer that were
treated with trastuzumab plus taxane (paclitaxel or docetaxel) as a first-line therapy and 34
controls who were patients with metastatic breast cancer but not selected for HER2/neu
amplification, and were only administered taxane without trastuzumab. Patients homozygous
for the FcγRIIa-131H allele showed 70% positive response, while heterozygous patients
(H/R) were 44% positive, and 40% of 131R homozygous patients responded positively. This
difference is not significant but there is a trend which shows that R-carriers are less likely to
respond to the trastuzumab treatment.
FcγRIIb-232
Musolino Study (2008)
55% of patients with the FcγRIIb-232I/I genotype were positive responders, of the
heterozygotic patients (I/T) 17% were responders and of the homozygous 232T patients 25%
were responders to trastuzumab. Found to be not significant.
Weng Study (2009)
Patients with the FcγRIIb-232I/I genotype had similar responses (64%) to the treatment
compared to patients with the I/T (67%) genotype or the T/T (50%) at 1 to 3 months posttreatment. There was also no significant difference at 6, 9 nor 12 months. About 20% of
patients with the I/I genotype had PFS at two years compared to the 43% of I/T patients, this
was not significant.
FcγRIIIa-818 and FcγRIIa-535
Pander Study
A randomized study with KRAS wildtype mCRC patients cohort (Pander et al., 2010).
Patients were part of a phase III CAIRO2 study. A cycle of treatment consisted of cetuximab
being administered at 400 mg/m2 on the first day and then 250 mg/m2 each week thereafter
for 3 weeks. The FcγRIIIa-818 C-carriers had a median 8.2 months PFS compared to patients
with the 818A/A genotype of 12.8 months.
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