[Incidence of colonic and rectal tumors as a function of the urban and rural characteristics of the residential area in the Isère district (1979-1985), France].

From 1979 to 1985, 1443 new malignant tumors of the colon and 1017 of the rectum appear in the departement of Isère (France). Using the urban category of "Zone de Peuplement Industriel et Urbain" (Z.P.I.U), we were able to classify place of residence within 3 strata, according to the proportion of inhabitants of the rural (or urban) type. For both sexes, incidence of colon carcinomas is higher in urban categories than in rural ones. For males, incidence of rectal carcinomas is higher within areas of the rural type. Going from the urban category of the rural one, "urban" being the level of reference. Relative Risks for men are 1,0.9 and 0.6 for the colon, and 1, 1.3 and 1.2 for the rectum. For women, RR's are 1,0.8, and 0.7 for colon, and 1,1.0, and 0.8 for the rectum. Same results are described in the literature, with higher risks for colon cancers in urban areas. Our results reporting lower incidence for rectal carcinomas in Isère among men, are in contradiction with other results in the literature. This work supports the idea that epidemiology of large bowel carcinomas should focus onto segments. Second, when categories of residence allow it, it is worthwhile looking at gradients that bring more information on the relation, than the simple dichotomy: urban versus rural.