Patterns of large bowel cancer by subsite, age, sex and marital status.

Incident cases of large bowel cancer from the Swiss canton of Vaud over the period 1974-88 were analyzed in relation to the distribution of site by sex, age, marital status and detailed subsite. A total of 1,968 cases were registered in males and 1,958 in females, corresponding to overall age-standardized (world) rates of 32.2/100,000 males and 22.4/100,000 females. The frequency of ascending and transverse colon cancer was lower in males (18.2% and 9.3%) than in females (23.1% and 10.0%, respectively), but cancers of the sigmoid colon and rectum were proportionally more frequent in males (34.0 and 30.0% versus 29.9 and 24.6% in females). Anal cancer accounted for 4.0% of large bowel cancers in females, but only 1.2% in males. Analysis of age-specific rates showed comparable values for ascending colon cancer in both sexes and in relation to each subsequent age group, as well as in sigmoid and rectal cancers up to middle age, while a male excess for the latter cancers became evident after age 55. A female excess for anal cancer was apparent in any subsequent age group. Information on marital status was available on 2,398 decreased subjects. Never married cases accounted for 12.2% of women and 8.1% of males. The excess of unmarried women was somewhat larger in the colon than in the sigma and rectum groups, but there was no evidence of excess of never married females for anal cancer. These data confirm that there are appreciable intersex heterogeneities in the descriptive epidemiology of various subsites of large bowel cancer, as well as complex interactions between sex and age, which may be related to female hormone correlates of intestinal carcinogenesis. Whatever the main biological mechanism(s), these data show noticeable similarities for both sexes in the descriptive epidemiology of cancers arising in the left colon and rectum, but noticeable differences with the right colon. Even more substantial are the differences with anal cancer, which should be linked to its venereal correlates.