? BrCA at 44 BrCA at 51 BrCA at 58 Tom 43 72

Example: Breast Cancer Sporadic Family clusters Hereditary 5%–10% 15%  20% An inherited predisposition underlies only a fraction of adult cancers

Relative Proportion and Case Load of ‘Hereditary Cancers’ in the US Breast10%18,000 Ovarian 5% 6,000 Colon10%15,000 Prostate10%25,000 Melanoma10% 3,000 Medullary thyroid25% 125 Retinoblastoma40% 70 Estimate of HereditaryHereditary Cancer type ProportionCases/Yr

Genes Involved in Carcinogenesis Oncogenes –Cancer results when inappropriately activated –dominant acting Tumor Suppressor Genes –Cancer can arise when function is lost or blocked –More likely (than oncogenes) to be involved in inherited predispositions to cancer Metabolism/detoxification Genes

Oncogenes Normal genes (regulate cell growth) 1st mutation (leads to accelerated cell division) 1 mutation sufficient for role in cancer development

Tumor Suppressor Genes Normal gene 1st mutation (susceptible carrier) 2nd mutation or loss (leads to cancer)

Genes Involved in Carcinogenesis Oncogenes –Cancer results when inappropriately activated –dominant acting Tumor Suppressor Genes –Cancer can arise when function is lost or blocked –More likely (than oncogenes) to be involved in inherited predispositions to cancer Metabolism/detoxification Genes

Risk of oral cancer from alcohol The influence of polymorphisms in alcohol dehydrogenase (ADH) Homozygous for the fast-metabolizing allele Homozygous for the slow-metabolizing allele Heterozygotes Number of alcoholic drinks per week Odds Ratio (log)

Tobacco-derived procarcinogen Metabolite A (nonreactive) Metabolite B Enz A Carcinogen Excreted in urine Bladder Cancer Enz B (in bladder wall) Sewer

Years of smoking Odds Ratio Increase in Bladder Cancer Risk in Smokers -as a function of an individual’s genotype Slow A, Fast B Slow A, Slow B Fast A, Slow B Fast/Fast

The Accumulation of Genetic Changes Underlies the Development and Progression of Cancer  Genetic pathways involved in tumorigenesis  Acquisition of invasive, metastatic, drug-resistant phenotypes  Somatic vs. germline

The Accumulation of Genetic Changes Underlies the Development and Progression of Cancer  Genetic pathways involved in tumorigenesis  Regulation of proliferation  Regulation of cell death (apoptosis)  Maintenance of DNA integrity chromosomal stability repair of damaged DNA correction of errors in DNA replication  Acquisition of invasive, metastatic, drug-resistant phenotypes  Somatic vs germline

The Accumulation of Genetic Changes Underlies the Development and Progression of Cancer  Genetic pathways involved in tumorigenesis  Acquisition of invasive, metastatic, drug- resistant phenotypes  Somatic vs germline

The Accumulation of Genetic Changes Underlies the Development and Progression of Cancer  Genetic pathways involved in tumorigenesis  Acquisition of invasive, metastatic, drug-resistant phenotypes  Somatic vs. germline –Somatic: only in the affected tissue –germline: aka constitutional, heritable DNA

Tumor Suppressor Genes Normal genes (prevent cancer) 1st mutation (susceptible carrier) 2nd mutation or loss (leads to cancer)

The Two-Hit Hypothesis First hit First hit in germline of child Second hit (tumor)

Human Genome Project Determine the complete nucleotide sequence of the human genome (3 X 10 9 ). Advances in DNA sequencing methodology and the sequencing of model organisms –C. elegans, E. coli, D. melanogaster Ethical, Legal, and Social Implications (ELSI) 1994: Comprehensive human genetic linkage map with an average marker density of 0.7 cM, based primarily on microsatellite markers.

D A1 B3 d A2 B2 d A3 B2 d A4 B4 D A1 B3 d A4 B4 d A2 B2 d A3 B2 d A3 B2 d A1 B2 d A4 B3 D A1 B3 d A1 B2 d A4 B4 d A1 B2 D A1 B3 Linkage Analysis Where is gene ‘D’

D A1 B3 d A2 B2 d A3 B2 d A4 B4 D A1 B3 d A4 B4 d A2 B2 d A3 B2 d A3 B2 d A1 B2 d A4 B3 D A1 B4 d A1 B2 d A4 B4 d A1 B2 D A1 B3 Crossover tells us that locus A is closer to “D” than is locus B

Breast Cancer Susceptibility Genes BRCA1 BRCA2 –Also associated with male breast cancer –Not associated with ovarian cancer ATM (Ataxia Telangectasia) –Heterozygotes ( % of the general population) may be at increased risk of breast cancer (≥5-fold) –Could account for as much as 8% of all cases of breast cancer in the USA Others (including p53)

Breast Cancer Risk (%) AGE (years) BRCA1-mutation carriers General population

Risk of a second cancer after breast cancer in BRCA1 mutation carriers AGE (years) Ovarian CA Breast CA Cumulative Risk

Causes of Hereditary Susceptibility to CRC Sporadic (65 %– 85%) Familial (10 %– 30%) Hereditary nonpolyposis colorectal cancer (HNPCC) (5%) Familial adenomatous polyposis (FAP) (1%) Rare CRC syndromes (<0.1%)

Age-Specific Penetrance for Colon Cancer in Hereditary Nonpolyposis Colon Cancer (‘HNPCC’) Percentage of individuals with an altered disease gene who develop the disease HNPCC mutation carriers General population Affected with colorectal cancer (%)

Risk of Colorectal Cancer (CRC) General population Personal history of colorectal neoplasia Inflammatory bowel disease HNPCC mutation FAP 5% 15%– 20% 15%–40% 70%–80% >95% Lifetime risk (%)

Cancer Risks in HNPCC Aarnio M et al. Int J Cancer 64:430, 1995 % with cancer Age (years) Colorectal 78% Endometrial 43% Stomach 19% Biliary tract 18% Ovarian 9%

The Potential of Genetic Testing Knowledge is Power Appropriate prophylaxis and screening Reduction of uncertainty “Sometimes the coin comes up heads” Genotype-directed therapy Informative for other family members

Caveats in Genetic Testing Multiple suspect genes for a given tumor type –especially a problem for the first member of a family to be tested Multiple cancers from a given germline mutation –?influence of the environment or modifier genes Multiple mechanisms of gene inactivation Mutation or polymorphism? –functional assays, once developed, will help Estimates of penetrance are difficult to apply –current estimates are derived from the most severely affected families

From DNA sequence to protein -- the effect of nucleotide changes...ATG GAT AGT TGC CAA... ...ATG GAA AGT TGC CAA Met Asp Ser Cys Gln......Me t Glu Ser Cys Gln... Missense mutations Nonsense mutations...ATG GAT AGT TGC CAA... ...ATG GAT AGT TGA CAA Met Asp Ser Cys Gln......Met Asp Ser STOP Frameshift mutations...ATG GAT AGT TGC CAA... ...ATG GAT ACG TTG CCA A Met Asp Ser Cys Gln......Met Asp Thr Leu Pro... Benign Polymorphisms (beware) Other Promoter function or RNA splicing altered

The Challenge of Genetic Testing -- not like other tests -- Probabalistic, not diagnostic Can affect other family members Uninformative results Uncertain effectiveness of preventive measures Fear of insurance loss Unanticipated psychological reactions Integration of genetic testing into decisions regarding primary therapy of a new cancer in a possible mutation carrier

? BrCA at 44 BrCA at 51 BrCA at 58 Tom 43 72