Clinical History:

A 55-year-old man had a test for occult blood performed on stool as a part of a routine examination. The test was positive. A colonoscopy was performed.

The lesion in image 9.1 proved to be a tubulovillous adenoma ("adenomatous polyp") that was benign. The lesions in images 9.2 (typical for descending colon) and 9.3 (typical for ascending colon) are colonic adenocarcinomas. In image 9.4 are seen hepatic metastases of colonic adenocarcinoma.

Questions:

1. Explain the genetics of these lesions

Over time, with turnover of the mucosal surface of the colon, there is an opportunity for mutations to arise in the cells. As mutations collect that turn oncogenes on or turn tumor suppressor genes off, the potential for origin of a clone of neoplastic cells arises. When few mutations are present, then an adenoma is present. As the adenoma grows and time passes, additional mutations may occur which lead to further loss of control of growth, and additional clones of neoplastic cells arise which may have more aggressive properties, such as the potential to invade and metastasize, characteristics for a malignancy.

2. What are potential screening tests for cancer?

History and physical examination are key starting points in the search for a possible cancer. Has there been a change in overall health? Are there constitutional signs and symptoms such as malaise, weight loss, or chronic pain? Are there physical findings such as a mass or an ulceration?

The problem is finding a cancer while it is still small and can be treated effectively, before it has spread and made eradication difficult. For example, by the time a breast cancer has reached the point where it is definitely palpable (about 1 cm), it has probably been present for seven years! Are there early detection methods? Several possibilities include:

1. Tumor markers

2. Radiologic imaging

3. Endoscopic studies

4. Cytologic screening