HORMONE REPLACEMENT THERAPY, REPRODUCTIVE HISTORY, AND COLON-CANCER -A MULTICENTER, CASE-CONTROL STUDY IN THE UNITED-STATES

Hormonal factors have been inconsistently associated with colon cancer risk in women. The associations between reproductive events, menstrua l factors, exogenous hormones, and colon cancer were evaluated in a la rge case-control study (894 female cases and 1,120 female age-matched population-based controls) in the United States, stratifying by age at diagnosis, tumor site, family history and other potential risk factor s. Overall, higher parity was associated with a marginally decreased r isk of colon cancer (five or more births compared with nulliparous: od ds ratio [OR] = 0.75, 95 percent confidence interval[CL] = 053-1.06) a fter adjusting for age at diagnosis, family history of colorectal canc er, vigorous lifetime physical activity, body mass index (BMI) (wt/ht( l.5)), total energy intake, and aspirin use. No important associations were observed for other reproductive or menstrual events. An inverse association between recent use of hormone replacement therapy (HRT) an d colon cancer was observed (OR = 0.71, CI = 0.56-0.89). Although inte raction terms were not significant, this inverse association appeared to be more pronounced for those with an older age at diagnosis; for th ose without a first-degree relative with colorectal cancer; and for th ose with a relatively low BMI. The reduced risk associated with HRT us e did not appear to be explained by other behaviors related to HRT use .