Download 26 - Rutgers Chemistry

Chapter 26: Cancer and Growth Control
Outline
 What is cancer?
 What are the types of cancer?
 How does cancer develop?
 What are the key properties of cancer?
 How do cancer cells behave in culture?
 Proto-oncogenes, oncogenes, tumor suppressor genes and DNA
repair genes
 Oncogenes: conversion from proto-oncogenes by gain-of-function
mutations; identification; activation by cancer-causing viruses
 Tumor suppressor genes: deactivation by loss-of-function
mutations; identification
 Examples of oncoproteins
 Examples of deactivation of tumor suppressor genes
 Examples of defects in DNA repair genes that lead to cancer
 Chromosomal abnormalities in cancer
 A brief look at cancer drugs that target oncoproteins
 Conclusion
 References
By Lisa Jablonski
Chemistry 544 –
Chemical Biology
Professor K.Y. Chen
May 3, 2010
What is cancer?
Cancer results from abnormal proliferation (increase in number) of cells in the body. A tumor,
also called a neoplasm, is any abnormal proliferation of cells which may be benign or
malignant. A benign tumor stays confined to its original location; it neither invades neighboring
normal tissue nor spreads to distant body sites. On the other hand, a malignant tumor is able
to both invade neighboring normal tissue and spread throughout the body via the circulatory or
lymphatic systems. The spreading of malignant tumors to distant body sites is called
metastasis. Cancer refers specifically to malignant tumors or cells.1
What are the types of cancer?
Carcinomas are malignancies of epithelial cells.1 Lung, breast and colon are the most frequent
carcinomas in the United States.2 Sarcomas are solid tumors of connective tissues, including
muscle, bone, fat, cartilage and fibrous tissue.1,2 Leukemias are malignancies of blood-forming
cells that grow in the bone marrow.1,2 Lymphomas are malignanies of immune cells that grow
in the lymph nodes.1,2 Tumors are further classified according to the origin tissue and the type of
cell involved.1
1
How does cancer develop?
Most cancers occur when a person is older, indicating that the development of cancer requires
several mutations (Figure 1).4
Figure 1: Epidemiology
of human cancers.4
Cancer begins with a mutation that provides a selective advantage for a cell, such as increased
ability to proliferate or survive; this process is called tumor initiation. That cell will divide and
create a population of clonally derived tumors cells; this process is called tumor clonality.
Further mutations occur within the cells of the tumor population, leading to tumor progression.
If one of the mutations provides a selective advantage, then cells with that mutation will more
dominantly proliferate; this process is called clonal selection. Further mutations occur that
lead to a more malignant and fast-growing tumor1. Figure 2 shows this process of cancer
development. Transformation is the change that a normal cell undergoes as it becomes
cancerous.5 Carcinogenesis is the process by which normal cells are transformed into cancer
cells.5
Figure 2: Process of cancer development.1
2
Throughout the cancer development process, mutations cause cancer cells to have increased
loss of normal growth control.6
The development and metastasis of human colorectal cancer illustrates how multiple
mutations lead to tumor progression and malignancy. The specific stages in tumor progression
of colon cancer, and the mutations that cause each stage, were determined largely by Bert
Vogelstein (Johns Hopkins University) and his colleagues. The order of the mutations, and not
just their accumulation, determines tumor initiation and progression (Figure 4).7
Figure 4a (top left): Mutations and their clinical effects in colon cancer. Figure 4b (top
right): A flow chart illustrating the same mutations and their clinical effects. 4
Individuals with inherited mutations in the APC gene, a gene that is involved in limiting cell
growth, have a hereditary predisposition for colon cancer.4 For example, familial
adenomatous polyposis (FAP) is an inherited predisposition for colon cancer in which
individuals form thousands of adenomas during their 20’s and 30’s.7 Individuals with FAP have
an inherited defect in the APC gene. The adenomas are benign, but because there are so
many of them, there is a high chance that one will become malignant.4 FAP is an example of a
“gatekeeper gene defect;” 4 gatekeeper genes regulate growth and differentiation pathways.9
Hereditary non-polyposis colon cancer (HNPCC) is caused by defective mismatch repair
genes. Patients with HNPCC form less adenomas, but these adenomas are more likely to
3
become cancerous because the defective mismatch repair genes cause increased mutations.4
HNPCC is an example of a “caretaker gene defect;”4 caretaker genes maintain genetic stability
and minimize mutation rates.8 Juvenile polyposis syndrome (JPS) and ulcerative colitis
(UC) are conditions in which stroma cells become abnormally proliferative, forming
hamartomatous polyps. These polyps cause nearby epithelial cells to become cancerous due
to an abnormal microenvironment.4 JPS and UC are examples of “landscaper gene defects;”4
landscaper genes encode proteins involved in the stromal environment.9 The risks of
developing colon cancer are heightened by possessing gatekeeper, caretaker or landscaper
defects (Figure 5).
Figure 5: Types of defects associated
with colon cancer, compared to sporadic
defects, and the probability of developing
colon cancer.4
What are the key properties of cancer?
In their paper “The hallmarks of cancer” published in 2000, Douglas Hanahan and Robert A.
Weinberg describe the key acquired capabilities of cancer:10
1) Self-sufficiency in growth signals. Cancer cells have reduced dependency on extracellular
growth factors. Why? Some cancer cells are able to produce their own growth factors,
leading to autocrine growth stimulation (the continuous autostimulation of cell division).1
Some cancer cells overexpress growth factor receptors (such as tyrosine kinase receptors)
or constitutively express different proteins in signal transduction pathways involved in cell
growth and proliferation.1,10
2) Insensitivity to antigrowth signals. Cancer cells lack density-dependent inhibition, the
process by which normal cells proliferate. In density-dependent inhibition, normal cells will
duplicate until they reach a certain cell density. Anti-growth signals will tell the cells to stop
proliferating and become quiescent (remain in G0 of cell cycle).1,10 By lacking densitydependent inhibition, cancer cells are insensitive to antigrowth signals and will continue to
proliferate. Cancer cells also lack the ability to terminally differentiate.10 Most fully
differentiated normal cells will either stop dividing or divide only rarely. Cancer cells fail to
undergo terminal differentiation, leading to abnormal proliferation.1
4
3) Evading apoptosis (programmed cell death). Cancer cells can survive in environments that
would trigger a normal cell to go through apoptosis.10
4) Limitless replicative potential. Cancer cells show telomere maintenance, allowing them to
multiply without limit.11
5) Sustained angiogenesis (formation of new blood vessels). In normal adults angiogenesis
is infrequent, occurring in women during their menstrual cycle, and in both men and women
during wound healing.11 Cancer cells use angiogenesis to continue growing and spreading.12
6) Tissue invasion and metastasis. Cancer cells are less adhesive than normal cells, which
helps them to invade other tissues and metastasize.1 Cancer cells also lack contact
inhibition, the process by which normal cells migrate. Normal cells will move until they
make contact with a neighboring cell. Once contact is made, further cell migration is
inhibited, and cells will adhere to each other. Because cancer cells lack contact inhibition,
they will move after contact is made with a neighboring cell and potentially move into
surrounding normal tissue.1
Cancer cells also bypass normal checkpoints that prevent mutations, resulting in further
downstream genetic instability.10
In his paper “What are the hallmarks of cancer?” published in 2010, ten years after Hanahan
and Weinberg’s paper, Yuri Lazebnik points out that self-sufficiency in growth signals,
insensitivity to antigrowth signals, evasion of apoptosis, angiogenesis and limitless replicative
potential are features of both benign and malignant tumors. The property that uniquely defines
malignant tumors is their ability to invade tissue and metastasize.12
Leukemias are an example of how the inability to fully differentiate leads to cancer. Normal red
blood cells are derived from a common stem cell (a hematopoietic stem cell), and will follow a
differentiation pathway through different progenitor cell types until they become fully
differentiated.4 Once completely differentiated, the red blood cells will stop dividing.1 Leukemia
occurs when a red blood cell does becomes “stuck” in a premature cell state where it can
continue dividing.1 A mutation in a progenitor cell or a mutation in a signaling protein telling a
progenitor cell to differentiate can lead to various types of leukemia (Figure 6).4
Figure 6: Red blood cell differentiation
pathways. Red and pink are stem
cells, green are progenitor cells.4
5
How do cancer cells behave in culture?
Normal cells, as described earlier, migrate according to contact inhibition and multiply following
density-dependent inhibition. When transformed, however, they lose contact inhibition and
density-dependent inhibition, and will grow and move on top of one another, forming 3-D
clusters of cells called focuses.1,4 The cancer cells are less attached to each other than normal
cells,4 and also appear rounder than normal because of their reduced attachment with
neighboring cells1 (Figure 7).
Figure 7a (top left): Scanning EM of normal 3T3 (mouse fibroblast) cells. Figure 7b (top right): Scanning
EM of 3T3 cells transformed by the Rous sarcoma virus.
Proto-oncogenes, oncogenes, tumor suppressor genes and DNA repair genes
We now know that the key properties of cancer, and that multiple mutations cause these
changes to occur. What genes are mutated?
The main genes mutated in cancer are proto-oncogenes, tumor suppressor genes and DNA
repair genes.14 Proto-oncogenes are genes that encode proteins that support cell growth and
proliferation, such as growth factors, growth factor receptors, signaling proteins and
transcription factors.4,15 Mutant, overactive forms of proto-oncogenes are called oncogenes;16
oncogenes encode for abnormal versions or quantities of growth-control proteins that cause the
growth-signaling pathway to become overactive.17 Oncoproteins are the proteins encoded by
an oncogene that cause transformation.21 Tumor suppressor genes are genes that encode
proteins that limit cell growth and division, such as cell cycle regulatory proteins. When tumor
suppressor genes are mutated, they are unable to stop cell growth, allowing the cell to grow and
divide.18 DNA repair genes are genes that encode proteins that correct errors that occur during
cell division, such as DNA mismatch repair genes.19 Mutations in DNA repair genes causes
increased mutations that can activate proto-oncogenes into oncogenes or deactivate tumor
suppressor genes.21 Mutations in other genes, such as pro- and anti-apoptotic genes, can also
contribute to cancer.20 The protein products of proto-oncogenes, tumor suppressor genes and
DNA repair genes are illustrated in Figure 8.
6
Figure 8: Protein products of proto-oncogenes, tumor suppressor genes and DNA repair genes in
controlling cell growth.21
Oncogenes: conversion from proto-oncogenes by gain-of-funtion mutations; identification;
activation by cancer-causing viruses
Gain-of-function mutations convert proto-oncogenes into oncogenes.21 In “Molecular Cell
Biology,” Lodish et al. describe three mechanisms by which proto-oncogenes are converted into
oncogenes:
•
•
•
“Point mutations in a proto-oncogene that result in a constitutively acting protein product.
Localized reduplication (gene amplification) of a DNA segment that includes a protooncogene, leading to overexpression of the encoded protein.
Chromosomal translocation that brings a growth-regulatory gene under the control of
different promoter and that causes inappropriate expression of the gene.”21
For all three mechanisms, a mutation in only one of the two alleles for the gene can cause
cancer.21
Oncogenes were first identified in cancer-causing retroviruses. Peyton Rous discovered the
Rous sarcoma virus (RSV) in 1911. The Rous virus contains a gene, src, that is required for
cancer initiation but not for viral function.4 In 1977, through experiments with the Rous virus, J.
7
Michael Bishop and Harold Varmus concluded that the src gene in the virus wasn’t an original
viral gene, but was a cellular gene that the virus acquired during replication in the host cell.22
The normal cellular gene is called c-src and is the proto-oncogene; the viral gene, v-src, is the
oncogene. 21
Unlike the Rous sarcoma virus, which is a fast-acting virus, most cancer-causing retroviruses
are slow-acting and cause cancer only have months or years have passed. These slow-acting
retroviruses do not carry oncogenes, but integrate their DNA into host genomes at locations that
affect cellular proto-oncogenes.21 For example, a retrovirus can insert its genes upstream of cmyc, a cellular gene that encodes a transcription factor involved in cell growth. If there is a
defect that prevents the right-hand viral LTR (long terminal repeats) from being transcribed, then
the right-hand viral LTR can act as a promoter to turn on c-myc (Figure 9a). Another possibility
is that the retrovirus inserts its genes upstream of c-myc, but in an opposite transcriptional
direction; in this case the viral LTR can act as an enhancer of c-myc (Figure 9b).
Figure 9: Activation of the c-myc
proto-oncogene due to
integrated retrovirus DNA.
Oncogenes can be identified by adding DNA from human cancer cells to a culture of mouse 3T3
cells (Figure 10). DNA from human cancer cells is added to a culture of mouse 3T3 cells.
About one mouse cell in a million will become transformed and form a focus. DNA from the
focus is isolated and transferred to another group of mouse 3T3 cells in order to isolate the
oncogene. The DNA from the second cycle is cloned into phages. Most human genes have Alu
sequences, which are repetitive DNA sequences, nearby. An Alu probe is added to the phages,
and it hybridizes only with the phage that received human DNA. The phage with the DNA also
contains the oncogene.21
8
Figure 10: The identification and
cloning of an oncogene.21
Tumor suppressor genes: deactivation by loss-of-function mutations; identification
Loss-of-function mutations deactivate tumor suppressor genes.21 Loss-of-function mutations
occur when a point mutation in a tumor suppressor gene prevents expression of the tumor
suppressor protein product, or causes a nonfunctional protein product.21 A deletion of a DNA
segment that includes a tumor suppressor gene will also lead to lack of expression of the tumor
suppressor protein.4,21
For loss-of-function mutations, both alleles for the tumor suppressor gene must be mutated.21
Chromosomal missegregation or mitotic recombination can cause both chromosomes to have
the mutant allele. This process is called loss of heterozygosity and leads to loss-of-function of
the tumor suppressor gene (Figure 11).4
Figure 11: Chromosomal missegregation
or mitotic recombination can cause a
chromosome pair to become homozygous
for mutant allele.4
9
The first tumor suppressor gene to be identified was the Rb gene, identified in patients with
inherited retinoblastoma. Individuals with this disease inherit a single mutant copy of the Rb
gene, and develop retinal tumors when they are younger and usually in both eyes. Individuals
are likely to develop tumors when they are younger and in both eyes because they already have
one mutant allele present. Tumors occur when a somatic mutation occurs in the other Rb allele,
causing loss-of-function of the gene. Figure 12 shows a pedigree of hereditary
retinoblastoma.21 In sporadic retinoblastoma, individuals inherit two normal copies of the Rb
gene; the copies eventually both become mutant through somatic mutations, leading to loss-offunction. Sporadic retinoblastoma is rarer than inherited retinoblastoma, occurs later in life and
usually only occurs in one eye. 21
Figure 12: Pedigree of hereditary
retinoblastoma. Individuals in red
inherited one mutant allele of Rb.21
Many human tumors contain mutant Rb alleles arising from somatic mutations.4 Another tumor
suppressor gene is BRCA1; women who inherit one mutant allele of BRCA1 have a much
higher probability of developing breast cancer.21
Alfred Knudson studied inherited and sporadic retinoblastoma and determined that two mutation
“hits” are required for loss-of-function of the Rb gene; his model of cancer causation by two
mutations is called the Knudson two-hit hypothesis.23
Examples of oncoproteins
Following are examples of oncoproteins that include virus-encoded activators of growth-factor
receptors; growth factor receptors; signal induction proteins; and transcription factors.
Overexpression of these oncoproteins can lead to cancer.
1) Virus-encoded activators of growth-factor receptors act as oncoproteins
Some viruses create proteins that can activate growth-factor receptors, causing overexpression
of the growth-factor receptor. These viral proteins act as oncoproteins, since they behave like
growth factors and cause overexpression of the growth-factor receptor.21
Spleen focus-forming virus (SFFV) is a retrovirus that disrupts the erythroid progenitor
differentiation pathway. For normal erythroid progenitors to become differentiated red blood
cells, the ligand Epo is needed to bind to the Epo receptor. SFFV encodes a mutant retrovirus
envelope glycoprotein, gp55, that is able to bind to and activate Epo receptors, causing
abnormal stimulation of proliferation of erythroid progenitors. This can lead to erythroleukemia
in mice (Figure 13).21
10
Figure 13: Virus-encoded glycoprotein
gp55 acts as an oncoprotein.21
The human papillomavirus (HPV) encodes a protein E5 that can bind to platelet-derived
growth factor (PDGF) receptors, causing the PDGF receptor to become activated; this can lead
to cervical cancer.21
2) Overexpression of growth-factor receptors
A point mutation coding for the transmembrane region of Her2, a growth-factor receptor, causes
Her2 receptors to dimerize and become activated even when not bound to a ligand. This
causes the Her2 to become constitutively active; the oncoprotein form of Her2 is called Neu
(Figure 14). The point mutation codes for glutamine instead of valine.21 Many human breast
cancers overexpress Her2.4 A point mutation for the epidermal growth factor (EGF) receptor
also causes overexpression. The mutation causes part of the ligand-binding domain of the EGF
receptor to be deleted, causing the EGF receptor to be constitutively activated (Figure 14). 21
Figure 14: Point
mutations causing
growth-factor
receptors Her2
and EGF to
become
overexpressed.21
11
A chromosomal translocation causes a different growth receptor, the Trk receptor, to become an
oncoprotein. Normal Trk receptors are activated by nerve growth factor (NGF). A chromosomal
translocation causes the extracellular domain of the Trk receptor to be fused with part of the
sequences encoding the tropomyosin protein; this causes dimerization of two Trk receptors
bound to tropomyosin and the activation of the receptors (Figure 15).21
Figure 15: Chromosomal translocation
causing Trk to become an oncoprotein.21
3) Overexpression of signal induction proteins
Src is a signaling molecule with kinase activity that is involved in the cell growth and
differentiation pathway26. Normal Src (c-Src) is inactivated when its tyrosine residue at position
527 is phosphorylated by another kinase, Csk. c-Src is activated when tyrosine 527 is
dephosphorylated by a phosphatase enzyme. In an oncogenic form of Src, such as v-Src,
tyrosine 527 is missing or altered; therefore, the oncogenic form of Src is constitutively active
(Figure 16).21
Figure 16: Comparison of structure of c-Src and v-Src. v-Src is missing the region containing tyrosine
527, and is therefore constitutively active.21
12
4) Overexpression of transcription factors
The overexpression of transcription factors can also cause transformation.21 When quiescent
fibroblasts are stimulated to proliferate by addition of serum containing PDGF, the c-Fos and cMyc genes are activated (Figure 17).21 c-Fos and c-Myc are proto-oncogenes that code for cFos and c-Myc, transcription factors that activate genes that code for proteins involved in cell
growth (specifically, proteins that cause cells to enter G1 and transition from G1 to S).
Therefore, if c-Fos and c-Myc are overexpressed, the cells are stimulated to grow and
replicate.21
Figure 17: Proto-oncogenes activated by
addition of PDGF in serum.21
In some cancers, multiple oncogenes are expressed that increase tumor formation (Figure 18).4
Figure 18: The effect of multiple
oncogenes on tumor formation.4
Examples of deactivation of tumor suppressor genes
Following are examples of the deactivation of tumor suppressor genes involved in the cell cycle
pathway, anti-growth signaling, and pro-apoptotic signaling.
1) Loss of activity of tumor suppressor proteins involved in the cell cycle pathway
Cells that enter the G1 phase of the cell cycle must past through a restriction point before they
enter the S phase. Passage through the restriction point is regulated by cyclins, cyclin13
dependent kinases (Cdks) and the Rb protein (Figure 18). If proteins that prevent the passage
of the cell from G1 to S are mutated, this can lead to uncontrolled cell growth.21 For example,
loss-of-function of Rb allows the release of E2F, a transcription factor that activates DNA
synthesis genes. Loss-of-function of p16, a cyclin-kinase inhibitors, leads to overexpression of
cyclin D, which causes hyperphosporylation of Rb and the relase of E2F. Both Rb and p16 are
tumor suppressor proteins. Some viruses also create proteins that can bind to Rb and inhibit it
(HPV - protein E7; SV40 virus – protein “T antigen”).21
Figure 18: Proteins involved in
restriction point control. Mutations in
the proteins highlighted in pink occur
commonly in human cancers.21
2) Loss of activity of tumor suppressor proteins that act as anti-growth factors
Tumorderived growth factor β (TGFβ) is a growth factor that inhibits the growth of different cells.
When TGFβ is deactivated, this contributes to the development of tumors. The binding of TGFβ
to receptors leads to the activation of Smad proteins, which move to the nucleus and activate
transcription of genes including p15. p15 functions to keep cells in G1 (Figure 19). Therefore, if
TGFβ or Smad proteins are deactivated, p15 is no longer expressed and cells can move past
G1. Most human pancreatic cancers contain deletions for the one of the Smad proteins,
Smad4.21
Figure 19: The TGFβ pathway.21
14
3) Deactivation of tumor suppressor genes that promote pro-apoptotic functions
p53 is a protein that stops cells in G1 with damaged DNA from proceeding to the S phase. More
than 50 percent of human cancers have mutations in the p53 gene. When DNA damage
occurs, kinases phosphorylate p53 to stabilize it and therefore increase its concentration. p53
activates transcription of p21, a cyclin-kinase inhibitor, that is involved in arresting cells in G1.
The increase in concentration of p53 also leads to the creation of proteins that cause apoptosis.
Therefore, if p53 is mutated, p21 is not activated and the cells can move into the S phase; proapoptosis signals are also not activated, even if cells contain damaged DNA.21
When conditions inside the cell are normal, the protein MDM2 binds to p53 to deactivate it.
Therefore if MDM2 is upregulated, this can lead to loss-of-function of p53. Similar to the case of
Rb, some viruses also create proteins that can bind to p53 and inhibit it (HPV - protein E6, SV40
virus - protein “T antigen”). Certain carcinogens such as benzo(a)pyrene (in cigarette smoke)
also cause mutations in p53.21
Examples of defects in DNA repair genes that lead to cancer
Defects in DNA repair genes, such as excision-repair and mismatch repair genes, can lead to
cancer. Indiviudals with genetic defects in certain DNA repair genes have a larger chance of
developing cancer; some of these genetic diseases and the types of cancer associated with
them are listed in Figure 20.21
Figure 20:
Human
hereditary
diseases
associated with
DNA-repair
defects.4
15
Chromosomal abnormalities in cancer
Tumor cells often have chromosomal abnormalities, such aneuploity (an abnormal number of
chromosomes) and translocations (elements from different chromosomes joined together). For
example, in Burkitt’s lymphoma, the c-myc gene is translocated from chromosome 8 to
chromosome 14. On chromosome 14 it is near an enhancer region and is therefore
overexpressed (Figure 21).21
Figure 21: Chromosomal translocation
in Burkitt’s lymphoma.21
Cancer cells also duplicate a DNA sequence, causing multiple (up to as many as 100) copies of
the DNA sequence to be present. When duplicated DNA sequences are lined up in the same
region of a chromosome, they form a homogeneously staining region (HSR) (Figure 22a).
The DNA duplicates can also exist as independent structures outside the chromosome; these
structures are called double minute chromosomes (Figure 22b).21
Figure 22a:
Homogeneously
staining regions.
Figure 22b:
Double minute
chromosomes.4
A brief look at cancer drugs that target oncoproteins
Cancer is treated with chemotherapy, radiation therapy, surgery and other methods. Gene
therapy chemotherapeutic drugs have been developed to target oncoproteins. Some examples
are Trastuzumab (Herceptin®), which targets the Neu protein in breast cancer patients, and
imatinib (Gleevec®), which targets the oncoprotein BCR-ABL in patients with chronic myeloid
leukemia (CML).24 Certain cancer drugs also target biomarkers on tumor cell; depending on the
types of biomarkers on a patient’s tumor cells, the drugs used to target those biomarkers can be
personalized.25
16
Conclusion
Cancer is complex, involving both overexpression of genes and proteins that stimulate cell
growth and underexpression of genes and proteins that limit cell growth. The loss-of-function of
one tumor suppressor gene may not cause cancer if other pathways are still intact to make up
for the tumor suppressor gene’s loss-of-function. But, as multiple mutations accumulate, they
increase the chance of developing cancer by disrupting more parts of the cell growth control
pathway.
References
1 Cooper, Geoffrey M. The Cell: A Molecular Approach. Second Edition. Copyright 2000.
Accessed from http://www.ncbi.nlm.nih.gov/bookshelf/.
2 http://www.cancer.gov/cancertopics/understandingcancer/cancer/Slide2
3 http://www.cancer.gov/cancertopics/understandingcancer/cancer/Slide3
4 Lectures notes “Cancer and growth control.” Dr K.Y. Chen, Rutgers University, May 2010.
5 http://www.cancer.gov/dictionary/
6 http://www.cancer.gov/cancertopics/understandingcancer/cancer/Slide53
7 Lecture notes “Colon Cancer.” Dr. Brian Keith, University of Pennsylvania, November 2003.
8 http://www.cancernetwork.com/display/article/10165/63458
9 Michor, F. et al (2004). “Dynamics of Cancer progression." Nature Reviews Cancer, 4:197205.
10 Hanahan, Douglas and Weinberg, Robert A (2000). “The hallmarks of cancer.” Cell, 100
(1): 57-70.
11 http://www.cancer.gov/cancertopics/understandingcancer/angiogenesis/Slide5
12 http://www.cancer.gov/cancertopics/understandingcancer/angiogenesis/Slide8
13 Lazebnik, Yuri. “What are the hallmarks of cancer?” Nature Reviews Cancer, 10:232-233.
14 http://www.cancer.gov/cancertopics/understandingcancer/cancer/Slide50
15 http://www.cancer.gov/cancertopics/understandingcancer/cancer/Slide43
16 Alberts, Bruce et al. Molecular Biology of The Cell. Fourth Edition. Copyright 2002.
17 http://www.cancer.gov/cancertopics/understandingcancer/cancer/Slide44
18 http://www.cancer.gov/cancertopics/understandingcancer/cancer/Slide46
19 http://www.cancer.gov/cancertopics/understandingcancer/cancer/Slide48
20 http://www.cancer.gov/cancertopics/understandingcancer/cancer/Slide50
21 Lodish, Harvey et al. Molecular Cell Biology. Fourth Edition. Copyright 2000. Accessed
from http://www.ncbi.nlm.nih.gov/bookshelf/.
22 http://nobelprize.org/nobel_prizes/medicine/laureates/1989/press.html
23 Knudson, Alfred (1971). “Mutations and Cancer: Statistical Study of Retinoblastoma.”
Proceedings of the National Academy of Sciences, 68 (4):820-823.
24
http://www.cancer.org/docroot/ETO/content/ETO_1_4x_oncogenes_and_tumor_suppressor_genes.asp
25 Thayer, Ann M (2010). “Biomarkers Help Hit The Bull’s-Eye.” Chemical & Engineering
News, 88 (17):8.
26 Martin, Steven G (2001). “The hunting of the Src.” Nature Reviews Molecular Cell Biology,
2:467-475.
17