1. A patient with retinoblastoma has a single tumor in one eye; the other eye is free of tumors. What steps would you take to try to determine whether this is sporadic or heritable retinoblastoma? What genetic counseling would you provide? What information should the parents have before a subsequent pregnancy?

2. Discuss possible reasons why colorectal cancer is an adult cancer, whereas retinoblastoma affects children.

3. Many tumor types are characterized by the presence of an isochromosome for the long arm of chromosome 17. Provide a possible explanation for this finding.

4. Many children with Fanconi anemia have limb defects. If an affected child requires surgery for the abnormal limb, what special considerations arise?

5. Wanda, whose sister has premenopausal bilateral breast cancer, has a greater risk for developing breast cancer herself than Wilma, whose sister has premenopausal breast cancer in only one breast. Both Wanda and Wilma, however, have a greater risk than does Winnie, who has a completely negative family history. Discuss the role of molecular testing in these women. What would their breast cancer risks be if a pathogenic BRCA1 or BRCA2 mutation were found in the affected relative? What if no mutations were found?

6. Propose a theory for why so few hereditary cancer syndromes, inherited as autosomal dominant diseases, are caused by activated oncogenes, whereas so many are caused by germline mutations in a tumor suppressor gene (TSG).