FeatureTumor Suppressor Genes Oncogenes Function of normal version Regulates cell growth and proliferation; some can induce apoptosis Promotes cell growth and proliferation Mutation (at cell level)Recessive (both copies of gene inactivated) Dominant (only one copy of gene mutated) Effect of mutationLoss of functionGain of function Germline mutations resulting in inherited cancer syndromes Seen in most tumor suppressor genes Seen in only a few oncogenes
Tumour suppressor gene (TSG) Caretaker genes: TSGs that are indirectly involved in controlling cellular proliferation by repairing DNA damage and maintaining genomic integrity, thereby protecting proto-oncogenes and gatekeeper TSGs from mutations that could lead to cancer. E.g., ATM, BRCA1/2, MLH1, MSH2, XPA. Gatekeeper genes: Tumor-suppressor genes that directly regulate cell proliferation. E.g., APC, CDKN2A, RB, TP53, VHL.
“Two-hit” hypothesis: Knudson,1971. This explains why hereditary retinoblastoma usually has an earlier age of onset and exhibits bilateral or multifocal occurrence more often than sporadic retinoblastoma.
Men 289,550 Women 270,100 26%Lung and bronchus 15%Breast 10%Colon and rectum 6%Pancreas 6%Ovary 4%Leukemia 3%Non-Hodgkin’s lymphoma 3%Uterine corpus 2%Liver/intrahepatic bile duct 2%Brain/nervous system 25%All other sites Lung and bronchus31% Colon and rectum9% Prostate9% Pancreas6% Leukemia4% Esophagus4% Liver/intrahepatic bile duct4% Non-Hodgkin’s lymphoma3% Urinary bladder3% Kidney and renal pelvis3% All other sites24% Colorectal Cancer is a Major Cause of Cancer Deaths in the United States Jemal et al. CA Cancer J Clin. 2007;57:43.
Colorectal Cancer (CRC) Factors associated with increased riskFactors associated with increased risk — Age (>90% diagnoses in individuals >50 years old) — Personal or first-degree family history of CRC, or adenomas, polyps or inflammatory bowel disease — Hereditary conditions Familial adenomatous polyposis (FAP)Familial adenomatous polyposis (FAP) Lynch syndrome(Hereditary nonpolyposis colorectal cancer, HNPCC)Lynch syndrome (Hereditary nonpolyposis colorectal cancer, HNPCC) — Ulcerative colitis — Obesity, physical inactivity — High-fat or low-fiber diet, inadequate intake of fruits and vegetables American Cancer Society. Cancer Facts & Figures 2005. National Cancer Institute. PDQ ® Physician Statement.
CRC Familial adenomatous polyposis (FAP): also called adenomatous polyposis coli (APC). an AD subtype of colon cancer that is characterized by a large number of adenomatous polyps. These polyps typically develop during the second decade of life and number in the hundreds or more (polyposis itself is defined as the presence of >100 polyps). FAP accounts for ~1% of all CRC. Penetrance of FAP is virtually 100%. More than 700 different mutations of the APC gene (5q21) have been reported, most of which are nonsense or frameshift mutations. Adhesion molecule. Interacts with β-catenin and when APC is mutated, the complex accumulates in the cell leading to transcriptional activation of other tumor promoting genesAPC: Adhesion molecule. Interacts with β-catenin and when APC is mutated, the complex accumulates in the cell leading to transcriptional activation of other tumor promoting genes
In late childhood and early adulthood, up to 1000 and more polyps develop in the mucous membrane of the colon (1). Each polyp can develop into a carcinoma (2). In about 85% of affected persons, small hypertrophic areas not affecting vision are present in the retina (congenital hypertrophy of the retinal pigment epithelium, CHRPE, 3).
FAP Persons with FAP have increased risks of other cancers, including gastric cancer (<1% lifetime risk), duodenal adenocarcinoma (5%-10% lifetime risk), hepatoblastoma (1% risk), and thyroid cancer. Mutations in the APC gene can also produce a related syndrome, termed attenuated familial adenomatous polyposis. This syndrome differs from FAP in that patients have fewer than 100 polyps (typically 10-20). FAP can also result from recessive mutations in MUTYH, a gene that encodes a DNA repair protein.
CRC Lynch syndrome or Hereditary nonpolyposis colorectal cancer (HNPCC) comprises 1–3% of CRC and is characterized by early-onset proximal CRC exhibiting MSI (microsatellite instability). Inherited as an AD, high-penetrance cancer syndrome, HNPCC individuals face a 50–70% lifetime risk of developing CRC, in addition to other malignancies. HNPCC is caused by mutations in any of six genes (MSH2, MLH1, MSH6, MLH3, PMS1/2) involved in DNA mismatch repair.
Gel electrophoresis of 3 different microsatellite polymorphic markers in normal (N) and tumor (T) samples from a patient with a mutation in MSH2 and microsatellite instability (MSI, MIN). Although marker #2 shows no difference between normal and tumor tissues, genotyping at markers #1 and #3 reveals extra alleles (blue arrows), some smaller, some larger, than the alleles present in normal tissue.
Genetics of Colon Cancer Mutations in tumorMutations in tumor –CIN: K-ras, APC, DCC, p53 (85%) –MIN: DNA MMR (15%) Mutations in patientMutations in patient –FAP, HNPCC, methylating genes Approximately 5% of CRC case are caused by inherited genetic mutations CIN = chromosome instable; APC = adenomatous polyposis coli; DCC = deleted in colon cancer [gene]; MIN = multiple intestinal neoplasia; MMR = mismatch repair; FAP = familial adenomatous polyposis; HNPCC = hereditary nonpolyposis colorectal cancer.
K-Ras First Biomarker in Colon CancerFirst Biomarker in Colon Cancer Predictive, Possibly PrognosticPredictive, Possibly Prognostic Predicts response to anti-EGFR drugsPredicts response to anti-EGFR drugs Is an example of how we can “personalize” cancer therapyIs an example of how we can “personalize” cancer therapy
LOH (loss of heterozygosity) Loss of a normal allele from a region of one cs of a pair,allowing a defective allele on the homologous cs to be clinically manifest. A feature of many cases of retinoblastoma,breast cancer,and other tumors due to mutation in a TSG.
A and B represent two microsatellite polymorphisms that have been assayed using DNA from a cancer patient's normal cells (N) and tumor cells (T)
Risk Factors of Pancreatic Cancer Family history (10 %) familial atypical multiple mole melanoma syndrome familial breast cancer (BRCA2) Peutz-Jeghers syndrome hereditary pancreatitis Diet Meat/fats Advancing age Male gender Diabetes Environmental factors smoking alcohol coffee (?) asbestos, pesticides, dyes
Hereditary Pancreatitis trypsin autosomal dominant early progressive fibrosis 40 x risk pancreatic cancer
Progression Model of Pancreatic Cancer Bardeesy et al., Nature Rev Cancer 2002
Gastric Cancer Diffuse type – linitis plastica Intestinal type