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Colonoscopy on a 58-year-old man reveals numerous adenomatous polyps. There is a significant history of colorectal cancer in his family. Carcinoma is detected on biopsy, and the tumor cells are found to have mutations in the proto-oncogene ras, and in the tumor suppressor APC gene. Which of the following types of mutations would tend to cause a neoplastic transformation due to its effect on the APC gene, but not on the ras proto-oncogene?
A. Activation by retroviral insertion
B. Gene amplification
C. Gene deletion
D. Insertion of an enhancer
E. Translocation to a more active gene region

cc..APC-tumor suppressor, K ras --protooncogene??

The correct answer is C. Tumor suppressor genes must be eliminated by some mechanism such as deletion, or a loss-of-function mutation in order to contribute to cancer.

Proto-oncogenes must be amplified (choice B), induced (choices A, D, and E), or have
gain-of-function mutations to contribute to cancer

agree.