COLON CANCER: ETIOLOGY, SYMPTOMS, DIAGNOSIS, AND TREATMENT
Colon cancer is the second most prevalent cancer in the United States, lung cancer being the first. It is also second to lung cancer in mortality rate (19:816). In 1990 there were about 155,000 new cases of colorectal cancer reported, and 61,000 deaths. The incidence in the general population is 5% (15:80). Although the number of cases is increasing, the rate is proportional to the population increase (8:301).
Yet in spite of the high incidence of colon cancer, we still do not have a sound basis for delineating the causes and mechanism of colon carcinoma growth (15:80). Nor do we have a means of curing the disease in every case. The five-year survival rate is about 50% (10:241). Nevertheless considerable advances have been made within the last 10 years in confirming the factors involved in the etiology (9:315), in early detection, in diagnostic techniques, and in treatment.
Endogenous etiological factors. It is now widely accepted that most carcinomas develop in previously benign adenomatous polyps, although some arise in normal, flat epithelium (10:242). Adenomas are pedunculated, sessile, or semi-sessile polyps that develop by increased cell division along the length of the crypt in the mucosal lining of the colon (6:4-6). Neoplasia is characterized by further increase in the rate of cell division, leading to decreased cell maturation. Adenomas can be distinguished from hyperplastic polyps which are not pre-cancerous, because the latter have cell division restricted to the lower half of the crypt and thus the surface cells are actually over-mature, as seen histologically (6:4).
Thus the presence of adenomas places the patient as well as first-degree relatives in the high-risk category. The degree of malignancy is correlated with the size and type of adenoma, the position in the colon, and the age of the patient (10:242-243). Most adenomas larger ...