Introduction

While cancers of the colon and rectum show some differences in their geographic and temporal distribution, it is usual to discuss them together in terms of causation.

Histology, classification and diagnosis

Epithelial tumors of the colorectum are adenocarcinomas. In many patients, such cancers are frequently associated with benign polyps and adenomas as well as dysplastic mucosal lesions which are believed to be precancerous (Ponz de Leon et al., 1987).

Geographic differences have been observed in the distribution by subsite (Schottenfeld & Winawer, 1982). Unfortunately, the anatomical boundary around the recto-sigmoid (which for international classification purposes is assigned to the rectum), is variable and the terms sigmoid and recto-sigmoid are often used interchangeably by clinicians. De Jong et al., (1972) concluded, however, that this made little difference to incidence rates. Non-epithelial tumors are discussed in Chapter 37.

Descriptive epidemiology

Incidence

For colon cancer, the highest male incidence rates are in the white population of Connecticut, USA (34.1). The highest female rate (29.0) is in the black population of Detroit (Fig. 28.1). Rates, in the range of 15 to 20, are observed in Canada and much of western Europe. In western Europe, the incidence tends to be more than twice that east of the Elbe River. In Asia and Latin America, rates are low to intermediate (10 to 15).