Section 24 Cancer Answer Key

24 Cancer Section 24.1 1. Which of the following is a characteristic of malignant tumors? a. localized to tissue of origin b. metastatic c. well differentiated d. sense signals that restrict cell division Ans: b 2. Gain-of-function mutations in which of the following genes typify colorectal carcinomas? a. APC b. p53 c. K-ras d. all of the above Ans: c 3. During metastasis, cells may undergo an epithelial-to-mesenchymal transition whereby there is a(n): a. increase in cell polarity. b. loss of cell-cell-adhesion. c. down-regulation in the expression of the Snail and Twist transcription factors. d. all of the above Ans: b 4. Which of the following promotes angiogenesis? a. EGF b. PDGF c. TGF d. VEGF Ans: d 5. In females, all the cells in a tumor have the same inactive X chromosome. The reason for this is that: a. all of the cells in a tumor are derived from a single progenitor cell. b. all late-stage tumors have chromosome abnormalities. c. multiple mutations are required for tumor induction. d. many tumor-suppressor genes are on the X chromosome. Ans: a 6. Name the six fundamental properties of malignant tumors. Which of these properties are amenable to study in a cell culture model of cancer? Ans: Malignant tumors exhibit (1) self-sufficiency in growth signals; (2) insensitivity to antigrowth signals; (3) evasion of apoptosis; (4) limitless replicative potential; (5) sustained angiogenesis; and (6) tissue invasion and metastasis. The first four properties are amenable to study in a cell-culture model because they are autonomous properties of cancer cells. In contrast, sustained angiogenesis and tissue invasion and metastasis involve the interaction of cancer cells with other tissues and are better studied in vivo. 7. Leukemias are different from most other classes of cancers. Which of the fundamental properties of cancer cells are likely to be lacking in leukemias and why? Ans: Leukemias are derived from blood cells or their precursors and proliferate as individual cells in the blood rather than as solid tumors. Because they already exist in the circulation, leukemias do not need to promote angiogenesis and likewise do not need to escape their tissue of origin and metastasize, although some leukemias may do so. 8. What is the multi-hit model of cancer? What data support this model? Ans: The multi-hit model proposes that multiple, successive mutations are required to produce a cancer cell. Many lines of evidence support this model, including the fact that tumor cells are clonally derived and possess the same genetic alterations. The increased incidence of cancer with age also supports the model. Finally, the cooperative effect of oncogenes in producing tumors in mice supports the model. 9. Describe the Warburg effect and how it applies to cancer cells. Ans: Otto Warburg described how cancer cells, regardless of the level of oxygen in their environment, produce large amounts of lactate as a result of using aerobic glycolysis to produce energy. 10. Which of the following is NOT a microscopic characteristic of tumor cells? a. high nuclear to cytoplasmic ratio b. greater percentage of mitotic cells c. larger size d. few specialized structures Ans: c 11. 2-hydroxyglutarate is produced in cancer cells: a. because cancer cells exhibit increased aerobic glycolysis. b. that have mutations in isocitrate dehydrogenase. c. to counteract all the lactate produced by aerobic glycolysis. d. all of the above Ans: b 12. Which of the following is NOT a role for the tumor microenvironment? a. tumor cells contain mutations b. interaction with immune cells c. neighboring cells relay information to cancer cells d. HCV-mediated inflammation Ans: a 13. Which of the following proteins involved in angiogenesis is paired correctly with its function? a. HIF – tyrosine kinase b. VEGF – receives a secreted signal to induce blood vessel growth c. oxygen sensor – transcription factor d. VEGF receptor – tyrosine kinase Ans: d 14. Which of the following interventions would NOT be likely to prevent tumor cells from metastasizing? a. inhibitors of adhesion molecules b. inhibitors of enzymes that degrade the basement membrane c. inhibitors of cell motility d. inhibitors of EGF Ans: a 15. A bone tumor sample appears to be heterozygous for a p53 mutation. The most likely explanation for this finding is: a. Mutated p53 is an oncogene. b. The p53 mutation is resulting in a dominant negative p53 protein. c. The p53 mutation is resulting in a premature stop codon, and no functional protein is made from that allele. d. There was a mistake in labeling the tissue sample—all tumors musts lack p53. Ans: b Section 24.2 16. Direct-acting carcinogens are those that: a. chemically react with nitrogen and phosphorous atoms in DNA. b. work in conjunction with cytochrome P-450 in the endoplasmic reticulum. c. are mainly reactive electrophiles. d. all of the above Ans: c 17. Telomerase: a. induces apoptosis. b. contains reverse transcriptase. c. is inactivated by Bcl-2. d. is active in all normal adult cells. Ans: b 18. Exposure to benzo(a)pyrene is most frequently associated with which type of cancer? a. lung cancer b. Burkitt’s lymphoma c. colorectal cancer d. breast cancer Ans: a 19. The first line of defense against point mutations is: a. BRCA1. b. cytochrome P-450. c. DNA polymerase. d. MSH2. Ans: c 20. Describe the differences between direct-acting and indirect-acting carcinogens. Ans: Direct-acting carcinogens have reactive electrophiles that react with nitrogen and oxygen atoms in DNA. These modified nucleotides distort the normal pattern of base pairing. Indirect-acting carcinogens are generally unreactive, waterinsoluble compounds. These compounds must first be converted to ultimate carcinogens by the introduction of electrophilic centers, usually by cytochrome P-450 enzymes in the liver. 21. Which of the following is NOT evidence that smoking causes lung cancer? a. Epidemiological rates of lung cancer dramatically increased after more people started to smoke. b. Exposure of lung cells to the active carcinogen found in cigarettes causes mutations in p53. c. Mutations in p53 are found in the same codons in patients with lung cancer who smoke as in cultured cells treated with benzo(a)pyrene. d. Epidemiological rates of lung cancer in women increased years after the rates in men increased. Ans: d 22. If colon cancers could be prevented by intervening in the earliest molecular changes during multi-hit progression, the molecule you would target for intervention would be: a. p53. b. Ras. c. APC. d. VEGF. Ans: c