Are there several colorectal cancers? Epidemiological data.

The knowledge of descriptive epidemiology of colorectal cancer is a prerequisite essential to a better understanding of the aetiology of the disease and the development of prevention strategies. This work provides an update of descriptive epidemiological data on colorectal cancer incidence in the world. In 1988-1992, incidence rates of colorectal cancer varied from 15- to 25-fold according to the geographical area. The highest rates were observed in Western countries, especially in North America, Australasia and, to a lesser extent, in northern and western Europe. The geographical distribution of colorectal cancer was similar in men and women. An examination of incidence data by subsites showed that the magnitude of geographical variations was more important for colon cancer than for rectal cancer. Contrasting with the male predominance for rectal cancer and, to a lesser degree, for left colon cancer, cancers of the right colon were found to be as frequent in women as in men. Examination of time trends during the last decades reveals a sharp increase in incidence of colorectal cancer in Japan and in eastern and southern Europe. On the other hand, incidence rates show some stagnation in North America and western Europe in recent years. In fact, there are some suggestions for differential time trends according to the anatomical subsite, with a recent proximal shift in the distribution of cancers of the large bowel in Western countries. In conclusion, descriptive epidemiological data support the notion that distinct pathogenic mechanisms may be involved in the carcinogenesis of the proximal and distal bowel.