Hormone replacement therapy, reproductive history and colon cancer; A multicenter, case-control study in the United States

Abstract

Hormonal factors have been inconsistently associated with coloncancer risk in women. The associations between reproductive events, menstrualfactors, exogenous hormones, and colon cancer were evaluated in a largecase-control study (894 female cases and 1,120 female age-matchedpopulation-based controls) in the United States, stratifying by age atdiagnosis, tumor site, family history and other potential risk factors.Overall, higher parity was associated with a marginally decreased risk ofcolon cancer (five or more births compared with nulliparous: odds ratio [OR]= 0.75, 95 percent confidence interval [CI] = 0.53-1.06) after adjusting forage at diagnosis, family history of colorectal cancer, vigorous lifetimephysical activity, body mass index (BMI) (wt/ht 1.5 ), total energy intake,and aspirin use. No important associations were observed for otherreproductive or menstrual events. An inverse association between recent useof hormone replacement therapy (HRT) and colon cancer was observed (OR = 0.71, CI = 0.56-0.89). Although interaction termswere not significant, this inverse association appeared to be more pronouncedfor those with an older age at diagnosis; for those without a first-degreerelative with colorectal cancer; and for those with a relatively low BMI. Thereduced risk associated with HRT use did not appear to be explained by otherbehaviors related to HRT use.