Reproductive factors related to the risk of colorectal cancer by subsite: a case control analysis

The authors hypothesized that reproductive factors of colorectal cancer, wh ich are probably mediated by endogenous hormones, would differ according to colonic subsite. Information on reproductive factors was obtained from 372 female colorectal cancer cases (113 proximal colon, 126 distal colon, 133 rectum) and 31 061 cancer-free controls at the Aichi Cancer Center Hospital , Japan, between 1988 and 1995. Multiple logistic analysis showed that late age at interview, family history of colorectal cancer among first-degree r elatives, menstrual regularity, late age at menopause, late age at first pr egnancy and late age at first full-term pregnancy were significantly associ ated with the risk of colorectal cancer. None of the risk factors were sign ificantly dissociated between colon and rectal cancer. In polytomous logist ic regression analysis, particularly noteworthy was the fact that the odds ratios for age at menarche (P-value for heterogeneity of odds ratios = 0.01 0), age at first pregnancy (P = 0.016) and age at first full-term pregnancy (P = 0.028) were significantly higher for distal than for proximal colon c ancer. This study supports the hypotheses that there might be an associatio n between reproductive factors and risk of colon cancer, and that the carci nogenesis of colon cancer, by subsite, might show aetiologic distinctions.