Only in the case of carcinoma of the uterine cervix is an opportunity for detection, early diagnosis, and even actual cancer prevention, presented comparable to that afforded by the rectum and colon.

Not only is this area one of the most common sites of cancer, but it is also readily accessible to detection techniques available to any physician in his office. As if this were not enough, cancer of the rectum and colon is thought to be preceded in many instances by a readily identifiable benign premalignant lesion that is susceptible to removal months or years before it undergoes malignant transformation. Thus true cancer prevention is possible.

Despite these facts, nearly 40,000 persons die of this disease in the United States yearly, adding grim emphasis to the need for wider understanding and application of present-day knowledge of the disease.

Often the rectum and colon are discussed as separate organs. We feel that the two are best thought of as one unit and will be so considered in this chapter.

Epidemiology. Incidence (Colon And Rectum Combined)

Mortality (Colon And Rectum Combined)

Rates And Ratios

Age

Trend Last Ten Years

Other Features

Unlike many other types of cancer, the incidence of the disease shows no established relationship to geographic area, religion, occupation, custom or habit, etc.

Furthermore, study of the age-adjusted incidence figures shows no significant trend toward increase or decrease of the occurence of cancer of the rectum and colon in the United States in recent years.

Etiology

Nothing is known about the fundamental or primary cause of cancer of the rectum and colon.

The fact that many of the malignant lesions appear to have their origin in benign polyps (adenomas) and that these in turn may have arisen from areas of mucosal hyperplasia is of great interest and clinical importance. (This aspect of the subject will be dealt with in detail below.) Still the basic etiology of these so-called premalignant lesions is unknown, and their management remains largely empirical.

The fact that long-standing ulcerative colitis may be complicated by the occurrence of carcinomas in the diseased bowel remains only a tantalizing clinical and pathologic observation from which no significant information has been gained regarding the etiology of the cancer.

Finally, the fact that most, if not all, of the individuals in fatnilies afflicted with so-called familial polyposis of the colon-a known genetically determined disease-will develop cancer of the colon has important implications regarding the possible role of genetic factors in the much less gross, but far more common, situation of single polyps. Superficially, there is little evidence for a familial predilection for ordinary polyps of the rectum and colon. The disease has been inadequately studied from a genetic standpoint, however.

Before leaving the subject of etiology, it should be noted that no thorough epidemiologic study has been done in an attempt to assess simultaneously all possible intrinsic and extrinsic factors.