Download Karyotypic Comparisons of Multiple Tumorous

ICANCERRESEARCH
56.855-859.February
15.19961
Karyotypic Comparisons of Multiple Tumorous and Macroscopically Normal
Surrounding Tissue Samples from Patients with Breast Cancer1
ManuelR. Teixeira,NikosPandis,GeorgiaBardi, JohanA. Andersen,and SverreHeim2
Department of Genetics, The Norwegian Radium Hospital and Institute for Cancer Research, Montebello, N-0310 Oslo, Norway (M. R. T., S. H.); Departments of Medical
Genetics (M. R. T., N. P., G. B., S. H.] and Pathology If. A. A.]. Odense University and University Hospital, DK-5tX1O Odense, Denmark; Department of Genetics, Saint Savas
Hospital. GR-11522 Athens, Greece [N. P., G. B.J; and Department of Clinical Genetics, University Hospital, 5-22185 Lund, Sweden (N. P., G. B., S. H.J
ABSTRACT
the moreremarkablebecause these analyses probablyseverely under
estimate the actual karyotypic variability present; the single, often
Many tumor tissuesare madeup of geneticallydifferentcell popula
small, sample routinely examined is unlikely to be representative of
all tumor areas (15). The spatial distribution of cytogenetically dis
parate tumor cell subpopulations and their possible relation to zonal
phenotypic heterogeneity are issues that have received practically no
lions, and the study of the causes and consequences of this heterogeneity
must play a central role in cancer research. We haveStudiedbreast cancer
clonal heterogeneity by cytogenetic analysis of 4123 cells from 52 success
fully short-term-culturedtumorous,metastatic,andmacroscopically
nor
madbreasttissuesamplesfrom 6 womenwith thisdisease.All 7 carcino
attention in the past.
We have recently reported a preliminary study of cytogenetic
heterogeneity in breast cancer, in which we demonstrated the local
ization of karyotypically distinct cell populations to separate intratu
morous domains (16). In this report, we extend that investigation by
the detailed analysis of 58 tumorous, metastatic, and macroscopically
normal breast tissue samples from another 6 patients with breast
cancer.
mas (one woman had bilateral disease) contained 1 to 9 karyotypically
related
as well as unrelated
clones, unevenly
distributed
among the tumor
quadrants. Two clonal chromosomeabnormalities were recurrent: inter
stitial 3p deletionswere found in 5 carcinomas,whereasdel(l)(q42) was
detected
in another
2 tumors.
Both successfully
analyzed
metastatic
le
sions (one axillary lymph node and one metastasisin the subcutls) con
tamed only one of several clones present in the primary
tumor, thus
exemplifyinga reductionin overallkaryotypiccomplexityduring card
noma spreading. In the case with the cytogenetically abnormal lymph
node,another karyotypically unrelated clone was found to Invadelocally
in the surrounding breast; also, histological evidenceof carcinoma infil
tration was seenin thesetissuesamples.In none of the other caseswere
clonalkaryotypicchangesfoundin macroscopically
normal,extratumor
ousbreasttissue.We concludethat a largeproportionof breastcarcino
mas are polyclonal with cytogenetically
panding
within
separate
domains
distinct cell subpopulations
of the growing
tumor.
MATERIALS
AND METHODS
Sevenconsecutivebreastcarcinomas(Table 1) with a diameterlargerthan20
mm were included in this study. None of the 6 women (cases VI and VII were
from a patientwith bilateraldisease)hadanyknownhereditarypredisposition
to cancer.Four samplesfrom each tumor (1 from each imaginary tumor
quadrant)wereobtainedandlabeledclockwiselA—D.In addition,samplesof
ex
Karyotypically
disparate neoplastic cells may have different capacities to display malig
nancy-specific features (e.g., to grow invasively and set up distant metas
macroscopically
tases). It is presumed that their synergetic action is required for the
full-blown carcinoma phenotype.
samples. Only when fat tissue dominated,
normal breast tissue were taken from at least 10 mm outside
the outer limits of the tumor and labeled 2A—D,in analogy with the tumor
so that no normal breast tissue was
visible in a given surrounding area, was no sample taken. A total number of 28
tumor samples,24 macroscopicallynormal breasttissuesamples,1 sample
from a subcutaneous
metastasis(labeled3), andS samplesfrom lymph node
INTRODUCTION
metastases(labeled 4) were obtained for cytogenetic analysis. The histopatho
It is now generally accepted that tumor tissues are heterogeneous
not only across the parenchyma-stroma borderline, but also among
subpopulations of truly neoplastic parenchymatous cells (1, 2). Anal
yses of tumor behavior and biology must take into account the causes
and consequences
of this phenotypic
heterogeneity
starting point the central tenet of the somatic mutation theory of
cancer (5, 6), have provided evidence that genetic mechanisms are
crucially involved in the generation of cell-to-cell and clone-to-clone
variation in breast tumors (7—1
1). In contrast to most chemistry-based
investigative methods, which yield pictures of an idealized average
tumor cell, cytogenetic techniques reveal the karyotypic constitution
of individual cells and thus are uniquely well suited to shed light on
the question of intratumor genetic heterogeneity (12). Multiple karyo
typically related, as well as unrelated, clones have indeed been de
tected in a high proportion of breast carcinomas (13, 14). This is all
Received 9/28/95; accepted I 2/1 1/95.
The costsof publicationof this article weredefrayedin part by the paymentof page
charges.This article mustthereforebe herebymarkedadvertisementin accordancewith
work
was
supported
by grants
from
the
Norwegian,
Danish,
and
Swedish
Cancer
2 To
whom
requests
for
reprints
should
be addressed.
and the resulting cells were plated out in 25-cm2 Primaria flasks
or Vitrogen-coated slide flasks. The cultures were fed an appropriate medium
plasms (3, 4). Several lines of research, all of them taking as their
I This
of slides from tissue imme
accordancewith WHO recommendations
(17),withoutprior knowledgeof the
cytogeneticfindings.
disaggregated,
standing of the mechanisms of tumorigenesis is to be achieved.
Breast carcinomas are among the most heterogeneoushuman neo
Societies. M. R. T. is the recipient of fellowship BD/3109/94 from Programa PRAXIS
XXI.
which included examination
Cells were short-term cultured and analyzed cytogenetically as described
previously (18). Briefly, all samples were mechanically and enzymatically
if a full under
18 U.S.C. Section 1734 solely to indicate this fact.
logical classification,
diately adjacent to the tissue processed for chromosome analysis, was made in
thatfacilitatesepithelialgrowthandwereharvestedafter5 to 8 days.Thecells
were exposed to demecolcine, dislodged by trypsinization, subjected to hypo
tonic shock in 0.05 M KCI, and fixed
in methanol:acetic
acid (3:1). Some
culturesin slideflaskswereharvestedin situ asdescribedby Mandahl(19).G
bandingwasobtainedwith Wright stain.Theclonalitycriteriaandthedescrip
tion of karyotypesfollowed the recommendations
of the ISCN (20).
The one samplesign testappliedto the differencesbetweenpairedobser
vations (21) was used to compare quantitatively the chromosomal findings in
tumors and grossly normal breast tissue areas.
RESULTS
Of the 58 specimensobtained for cytogenetic analysis, all 28 tumor
samples, 22 of 24 macroscopically normal surrounding breast tissue
samples(only samples2A and 2B from caseI did not grow in culture),
1 of S lymph node metastases(only in case VI was the outgrowth
epithelial; the fibroblastic cells growing from the other samples had a
46,XX karyotype), and the locally metastatic lesion were successfully
cultured. A total number of 4123 metaphases were analyzed (2354
855
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KARYOTYPIC HETEROGENEITYIN BREAST CARCINOMAS
dataClinico-pathological Table 1 Clinico-pathological
normalbreast
[del(1)(q42)] that was quantitatively dominant in the tumor were
detected. Microscopically, these samples were shown to contain both
in situ and invasive lobular carcinoma areas. In all the other cases, no
clonal chromosome abnormalities were found in the surrounding
data on 58 tumorous,metastatic,and macroscopically
cases.Case
tissue samples obtained for cytogenetic analysis from 7 breast cancer
Age
Tumor size
Histology―1-153/94
no.
(yr)
(mm)
Nodal
status
59
+
30
Samples@'
breast tissue. Except for 2A—D
of case VII, none of these samples
DC2A-B
IA—D
N2C-D
EH4
contained microscopic evidence of carcinoma spreading. The fre
quencyof nonclonalchanges in the grossly normalbreasttissue varied
M11-182/94
47
23
—
42
from 2.2% to 5.7% (median, 3.3%), and hence no statistically signif
icant difference was found in the paired comparison of tumorous
versus nontumorous samples in this regard (P = 0.7).
IDC' +
IDC+DCISID
DCIS2A,
2C-D
DC2A,
1A—D
EH3 2C-D
M4
N111-242/94
40
DCISlC
lA—B
+
DISCUSSION
MIV-250/94
54
36
+
Five of the 7 breast carcinomas were shown to contain a
del(3)(p12—13pl4--21) in 2—4tumor samples (Table 2). In casesI, III,
CDC2A
1A-D
EH2B-D
N4
and VII, this deletion was the sole chromosomal abnormality of the
clone, but in the remaining two cases (IV and V), extensive clonal
MV-271/94
77
25
—
DCIS2A,
1A—D
44
45
+
2D
ILC2A-D
1A-D
EHVI-257/94
IDC' +
LCIS4
NC+ ILC +
MVll-258/94
44
55
+
ILC2A-D
lA-D
LCIS4
a Samples
IA—D
originate
from
tumor
mass,
2A—D
from
NC+ ILC +
M
macroscopically
normal
surrounding breast tissue, 3 from a subcutaneous metastasis, and 4 from axillary lymph
node metastases.
b DC,
ductal
carcinoma;
IDC,
invasive
ductal
carcinoma;
DCIS,
ductal
carcinoma
in
studies; using RFLPs, Sato et a!. (24) detected loss of heterozygosity
situ; CDC, comedo type ductal carcinoma; ILC, invasive lobular carcinoma; LCIS, lobular
carcinoma in situ; EH, epithelial hyperplasia; N, normal breast tissue; M, metastasis.
C Quantitatively
dominant
histologic
evolution had occurred. These results are in keeping with our earlier
findings in sporadic breast cancers (13, 22) as well as in breasts of
women with a hereditary predisposition to this disease(23); the results
support our previous conclusion that interstitial deletions of the short
arm of chromosome 3, with 3pl3—l4as a minimally common deleted
segment, are consistent primary changes in breast tumorigenesis.
Recent evidence that a tumor suppressor gene important in carcino
mas of the breast maps to this region has come also from molecular
at 3pl3—l4.3 in 47% of the tumors they examined. Chen et al. (25),
who combined fluorescence in situ hybridization and RFLP analyses,
concluded that the dominant mechanism of allelic loss at 3p in breast
finding.
from the tumors, 1720 from grossly normal breast tissue, and 49 from
the lymph node of case VI and the subcutaneousmetastasis of case
III). The complete karyotypic data are presented in Table 2.
All 7 breast carcinomas were shown to contain clonal chromosome
abnormalities in 3—50%
(median 26%) of the cells analyzed; 86% of
cancer was physical deletion. Buchhagen et a!. (26), on the other
hand, demonstrated three mechanisms by which the putative tumor
suppressor gene in 3pl4—2lcould be inactivated: homozygous dde
tion, rearrangement, and hypermethylation.
The secondchromosomal anomaly detected in more than one tumor
in our study was del(l)(q42), which was found in several samples of
the tumor samples (24 of 28) were karyotypically abnormal. Non
clonal changes were found in 1.1—5.1%
(median 3.5%) of the tumor
cases II and VI (Fig. 3). Similar terminal lq deletions have been
cells in each case. One to 9 clones were found in each tumor, unevenly
distributed among the tumor quadrants (Fig. 1 gives an idea of how
that this aberration must be accepted as identifying a ninth karyotypic
the various clones were spatially arranged in cases III and VI). Two
to 7 cytogenetically unrelated clones were detected in 4 of the carci
nomas; related clones were found, in addition, in 2 of them. Complex
effect of del(1)(q42) is unknown,but loss of a tumorsuppressorlocus
could be the relevantoutcome.
clones were detected in case IV only, where they coexisted with
other simple and cytogenetically
unrelated clones. In all other
reported previously both by us (27) and others (28), and it is now clear
subgroup in breast carcinomas (13). The fundamental pathogenetic
The patient with synchronous bilateral disease had the two recur
rent cytogenetic abnormalities mentioned above in her right-sided
(case VII)
carcinomas, the clones detected were near-diploid or, in most
instances, pseudodiploid.
Two clonal chromosome abnormalities were recurrent. Interstitial
3p deletions spanning bands p12—21were detected in 2—4samples of
S carcinomas (minimal common deleted segment 3pl3—l4; Table 2).
Extensive clonal evolution of the clone with 3p—was seenin casesIV
and V. In case III, two different 3p deletions (Fig. 2) were seen in the
tumor samples, and one of them, del(3)(pl3pl4), was also found in
the subcutaneous metastasis. The second recurrent chromosome ab
normality was the del(l)(q42) detected in several samples of casesH
and VI (Fig.3). In addition, band 1q42 was also rearranged in the
t(l ; 12) found in case V as one of many clonal chromosome abnor
malities. The woman with bilateral breast carcinoma had a
del(3)(pl2pl4) as the sole clonal aberrationin her right tumor (case
VII) and a del(l)(q42) as the quantitatively dominant clonal abnor
mality in her left tumor (case VI).
Clonal chromosome abnormalities were found in the macroscopi
and left-sided
breast tumors (case VI), respectively.
Be
cause no karyotypicaberrationwas common to the two carcinomas,it
would seemthat they arose independently as two primary tumors. We
have shown previously that this is not always the case in bilateral
breast cancer; the cytogenetic evidence indicates that the disease
process spreads from one breast to the other in some instances (27).
Carcinoma cells with highly complex cytogenetic abnormalities
were detected only in case IV; all the other carcinomas were karyo
typically abnormal but had pseudo- or near-diploid clones. Presum
ably, these aberrations gave the cells a proliferative advantage. Ap
proximately 30 tissue massdoublings are required for a tumor to reach
clinical detectability (29), and the fact that many of the karyotypic
abnormalities were detected in many cells in several tumor samples
indicates that they must have been acquired at an early disease stage.
With the methods we use, only about 20% of karyotypically abnormal
breast carcinomas are seen to contain highly complex, non-near
diploid clones (13), even when a detailed analysis of multiple tumor
cally normaltissue surroundingthe breastcarcinomain case VI; in all
samples is performed(Ref. 16 and present report). Flow cytometry
studies indicate that about half of all breastcarcinomashave diploid
4 samples
DNA histograms (30). The combined data are in keeping with theo
(2A—D), cells carrying
the same karyotypic
aberration
856
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KARYOTYPIC HETEROGENEITYIN BREASTCARCINOMAS
Table2 Karyotypicdata
Summaryof cytogeneticfindings in 52 successfullyculturedtumorous,metastatic,and mascroscopicallynormalbreasttissuesamplesfrom 7 breastcancercases.
Case
Sample'@
III
IA
46,XX[30]
IB
1C
ID
2C
2D
46,XX,del(3)(p13p14)[2)/46,XX[421
46.XX[451
46,XX,del(3)(p13p14)[41/46,XX[68l
46,XX[62]
46,XX[35]
lA
46,XX,del(1)(q42)[3J/46,XX[30]
lB
1C
46,XX,del(1)(q42)[91/46,XX[29]
46,XX(50]
ID
46,XX,del(l)(q42)[21/46,XX[l7]
2A
2C
46,XX[62]
46,XX[43]
2D
46,XX[40]
IA
lB
IC
46,XX,del(3)(p13p14)[9J/46,XX[54]
46,XX,t(l;19)(p22;p13)[51/46,XX[50l
46,XX,del(3)(p13p14)[45J/92,XXXX,idemx2[31/46,XX,t(l;2)(p36.3;p21)[421/92,XXXX,t(l;2)(p36.3;p21)
lD
2A
2C
2D
46,XX,del(3)(p12p14)[19]/46,XX,del(3)(p13p14)[4Y46,XX,t(1;2)(p36.3;p21)[ll/46,XX[73]
46,XX[l07]
46,XX[73]
46,XX[75]
x2[5]/46,XX,del(3@pl2pl4)[9J/47,XX,+i(l)(ql0)[2]/46,XX[l38]
IV
3
46,XX,del(3)(p13p14)[41/46,XX[25]
IA
62—64,XX,—X,add(1)(pll),der(l;13)(qlO;qlO),der(2)t(1;2)(p13;p25),der(3)del(3)(p13p21)inv(3)(p2.3p26),—4,—5,+6,
—l4,—l4,der(14)(qter--+p1?::hsr::8q11--s8qter),—15,del(l6)(ql3),der(17)del(17@pl1)t(7;l7@q22;q25),—2O,add(2l)(pl1),—22,
—22,+3—Smar[cp2OJ/46,XX[24]
lB
(qter—øpl?::hsr::$qll--$qter),—lS,del(16)(q13),der(17)del(17)(pll)t(7;17)(q22;q25),—20,add(21)(pll),—22,—22,+3—Smar[cp2.5]
/58—62,idem,der(9;15)(qlo;qlO),der(lO)t(l0;l5)(q23;q15),+
l6[cp3]/124—128,idemx2[cp2l/46,XX,add(2)(p24)[4]
/46,XXI(l;7)(p36;p13)[2]/46,XXt(3;6)(q29;q16)[2]/46,XX[70]
lC
::hsr::Sqll—.Sqter),—15,del(16)(q13),der(17)del(17)(pll)t(7;17)(q22;q25),—20,add(2lXpll),—22,—22,+3—Smar(cp3J/46,XX[15]
46,XX[25]
46,XX[l25]
46,XX[108]
46,XX[82]
46,XX[86]
ID
2A
2B
2C
2D
V
1A
lB
IC
46,XX,del(3)(p12p14)[41/46,XX[73]
48,XX,+7+der(16)t(8;16)(ql l;ql3)X2,—l6[4l/46,XX,del(3)(p12p14)[31/46,XX[68]
(q22;q32),der(l9)t(3;19)(pl2;p13)del(3)(pl2pl4)[I
1]/46,X,der(X)t(X;2)(p22;p23),der(l)t(l;2)(q24;p14)t(X;2)(p22;p23),der(2)
t(l;2)(q24;pl4)[l8]/46,XX,t(4;7)(q23;p2l)[l l}/46,XX,t(I;16)(q21;ql3)[lO]/46,XX,der(l)t(1;12)(q42;q24),t(2;5)(q14;pl3),
der( I 2)qter—@q24.
1::pl3—@q24.
1:: 1q42—+lqter)[6]/46,XX[1281
VI
VII
a Samples
ID
46,XXt(5;l2)(q13;qls)[3I1/46,XX,del(3)(p12p14)[61/46,XX[l23]
2A
2D
46,XX[95]
46,XX[l03]
IA
46,XX,del(1)(q42)[11V46,XX,t(l;12)(plO;qlO)[81/46,XX,del(1)(q12)[3]/46,XX[46]
lB
IC
1D
2A
2B
2C
2D
4
IA
lB
46,XXdel(1)(q42)[541/92,XXXX,idemx2[6]/46,XX,del(1)(q12)[31/46,XX[151]
46,XX,del(1)(q42)[13J/46,XX,del(1)(q12)[4]/46,XX[73]
46,XX,del(l)(q42)[3]/46,XX[22]
46,XX,inv(l l)(p15q23)[26]/46,XX,del(l)(q42)[41/46,XX,t(l;9)(p21;p2l)[21/46,XX[l26]
46,XX,add(I l)(q14)[5l/46,XX,del(1)(q42)[1l/46,XX[34]
46,XX,del(l)(q42)[21/46,XX[32]
46,XX,del(l)(q42)[1J/46,XX[23]
46,XX,del(l)(q12)[41/46,XX[12]
46,XX,del(3)(p12p14)[91/46,XX[29]
46,XX,del(3)(p12p14)[1531/92,XXXX,idemx2[61/46,XX[79]
1C
1D
46,XX,del(3)(p12p14)[7]/46,XX[28]
46,XX[50)
2A
2B
2C
2D
46,XX[50]
46,XXI147]
46,XX[76]
46,XX[45]
1A—D originate
from
the
tumor
mass,
2A—D from
the
macroscopically
normal
surrounding
breast
tissue,
3 from
a subcutaneous
metastasis,
and
4 from
an axillary
lymph
node metastasis.
b Clones
present
in more
than
one
sample
in each
case
are shown
in bold.
retical scenarios stipulating that whereas some neoplasms show ex-
unevenly distributed within the tumor mass (Fig. 1). This demon
tensive genetic divergence during tumor progression, others remain
strates that cytogenetically distinct cellular subpopulationsexpand
genetically stable throughout, or may actually become less diverse as within separatedomains in the growing tumor, as was also indicated
the disease goes from bad to worse (31). The actual testing of how by the results of our pilot study (16). Similar regional karyotypic
these assumptions apply to breast cancer would require longitudinal
heterogeneity was recently shown in a detailed investigation of a
monitoring of the neoplastic process with multiple samplings at sev- low-grade glioma (32). The asymmetric clonal distribution highlights
eral points in time, which is hardly feasible.
the need to sample multiple sites if one wants to obtain a truly
Multiple clones were detected in 4 breast carcinomas, always representative, balanced picture of the tumor's genetic characteristics.
857
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KARYOTYPIC HETEROGENEfl@Y
IN BREAST CARCINOMAS
Much the same conclusion has also been reached via other investiga
tive approaches. For example, because the DNA index is underesti
mated, the prognostic significance of flow cytometry data in breast
cancer has been found to be unnecessarily low when only one sample
11
del(1)(q42)
3 =
Fig. 3. Partialkaryotypesandideogramillustratingthe identical lq terminaldeletions
in cases II (right) and VI (left).
is analyzed; at least 4 tumor samples must be examined to detect all
stemlines with a larger than 90% probability (33). It seemsclear that
analysesof the genomic constitution of breast carcinomas (be it at the
total DNA, chromosomal, or genic level) that do not take this factor
into consideration should be interpreted with caution.
More often than not, multiclonality in the form of cytogenetically
unrelated clones is seen in breast carcinomas (13, 14). In this series,
4 of the carcinomas contained 2—7
independent clones. Is this type of
intratumor karyotypic heterogeneity compatible with the most com
mon interpretation of the somatic mutation theory of carcinogenesis
(5), which says that the process begins with a single mutated, and
hence transformed, cell? One of the possible explanations that have to
be taken into account is that the unrelated clones might reflect somatic
cell mosaicism in breast tissue existing prior to the appearance of any
@
2C
neoplasia. No
histologically
surroundings,
nonneoplastic
2B
Fig. 1. Spatialrelationshipof the different aberrantclonesfound in the variousintra
andextratumoroussamples,aswell asin the metastaticlesions,of casesifi (top) andVI
genetically unrelated clones detected in several independent cultures
(bottom). Samples 1A—Dwere from each quadrant of the tumor mass, samples 2A—Dwere
from the macroscopically normal surrounding breast tissue, sample 3 was from a subcu
taneous metastasis, and sample 4 was from an axillary lymph node metastasis. Different
graphic texture patterns represent cytogenetically unrelated clones (see Table 2 for
detailed karyotypic information). Similar patterns in each case represent the same or a
cytogenetically related clone.
‘}F
1!
liii
t(1 ;2)(p36.3;p21)
J(@
del(3)(p12p14)
clonal chromosome abnormalities were detected in the
benign breast tissue samples taken from the tumor
however, nor did previous cytogenetic analyses of
breasts reveal such changes (34—37).The large, cyto
del(3Xp13p14)
from separate tumor areas but not elsewhere in the breast evidenfly
possessa proliferative edge; to doubt that they are part of the neo
plastic parenchyma in the face of the evidence now at hand seems
illogical to us.
The conclusion that the near- or pseudodiploid clones really have a
malignant potential gains further credibility from the findings in the
metastatic lesions. In case VI, a del(l)(q42) was detected in all tumor
samples as well as in the 4 surrounding areas, where small foci of in
situ and invasive lobular carcinoma were found microscopically.
Another clone, characterized by a del(1)(q12), was present in 3 of the
tumor samples and was the only one to be detected in the axillary
lymph node metastasis. It appears that whereas cells carrying the
del(1)(q42) were able to invade locally within the breast, the karyo
typically unrelated cells with del(l)(q12) were the ones to metastasize
via the lymphatic system (the karyotypic relationship between breast
carcinomas and their lymph node metastasesin this and other cases
will be dealt with more extensively by Pandis et al.3). A similar
situation had occurred in case HI: only 1 of the 7 clones present in the
tumor (3 of them detected in multiple samples; Fig. 2) was found in
the subcutaneous metastatic lesion. Finally, the frequency of non
clonal changes in tumor and surrounding tissue cultures was similar,
arguing against the hypothesis that the karyotypically unrelated clones
with relatively minor chromosomal aberrations should be a conse
quence of some kind of clastogenic effect exerted by the actual
neoplastic cells on neighboring stromal or nonneoplastic epithelial
cells.
Fig. 2. Partialkaryotypesandideogramsof thethreecytogeneticallyunrelatedclones
detected in more than one tumor sample in case III.
3 Pandis
et aL,
manuscript
in preparation.
858
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KARYOTYPIC HETEROGENEITYIN BREAST CARCINOMAS
Although it seemsunavoidable to conclude that the various karyo
typically unrelated clones are part of the neoplastic parenchyma, the
question still remains whether they are truly independent or have
arisen as a consequence of clonal evolution, in which case they
must be supposed to share a submicroscopic tumorigenic mutation
that preceded and presumably induced the chromosome-level
changes. Whenever multiple tumor samples were analyzed (Ref. 16
and herein), the proportion of breast carcinomas with this type of
multiclonality could be seen to be as high as 70%. The hypothesis
of a unifying submicroscopic mutation in most breast carcinomas
does not explain why karyotypic multiclonality is so much more
common here than in, e.g., hematological (38) or mesenchymal
(39) neoplasms; evidently, a polyclonal model of carcinogenesis
would be the one that best accommodates the cytogenetic data. We
underscore that the finding of monoclonality in polymerase chain
reaction-based analyses of X-inactivation patterns in breast carci
nomas (40) does not make our position untenable. That technique
identifies a tumor as monoclonal whenever a cell subpopulation
makes up 50% or more of the total, and the presence of additional,
independent, smaller clones therefore cannot be ruled out on the
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Downloaded from cancerres.aacrjournals.org on June 14, 2017. © 1996 American Association for Cancer Research.
Karyotypic Comparisons of Multiple Tumorous and
Macroscopically Normal Surrounding Tissue Samples from
Patients with Breast Cancer
Manuel R. Teixeira, Nikos Pandis, Georgia Bardi, et al.
Cancer Res 1996;56:855-859.
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