POSTMENOPAUSAL HORMONE USE AND RISK OF LARGE-BOWEL CANCER

Background: The epidemiology of large-bowel cancer suggests a role for endocrine factors in its development, Although analytic studies have not consistently provided evidence for an association between reproduc tive history and large-bowel cancer, some relatively small studies hav e observed a reduced risk among women:;using postmenopausal hormone re placement therapy (HRT). Purpose: This study was planned to evaluate m ore precisely the relationship between HRT and the risk of colon and r ectal cancers, Methods: Female residents of Wisconsin aged 30-74 years with a diagnosis of colon or rectal cancer within 2 years were identi fied through a statewide tumor registry. Control subjects were randoml y selected from lists of licensed drivers if the case subjects were le ss than 65 years old and from lists of Medicare beneficiaries if they were 65-74 years old, Information on postmenopausal hormone replacemen t use, medical history, and family history was obtained in telephone i nterviews, After premenopausal women were excluded, 694 case subjects and 1622 control subjects remained for analysis, The odds ratios and 9 5% confidence intervals (CIs) obtained from conditional logistic regre ssion models were used to estimate relative risks (RRs), All RRs were adjusted for age, family history of large-bowel cancer, use of screeni ng sigmoidoscopy, and recent alcohol consumption, Results: Compared wi th postmenopausal women who never used HRT, recent users had an RR of 0.54 (95% CI = 0.36-0.81) for colon cancer and an RR of 0.91 (95% CI = 0.54-1.55) for rectal cancer. This inverse association was observed a mong users of both estrogen only and combined estrogen and progestin p reparations, Decreasing time since last use was inversely associated w ith colon cancer risk (P for trend <.001). The effect of HRT appeared to be stronger among women at lower absolute risk of colon cancer, par ticularly among women with lean body mass, Conclusions: Use of HRT was associated with a statistically significant reduced risk of colon can cer, In contrast, no statistically significant relationship was observ ed for rectal cancer, Given the widespread use of postmenopausal hormo nes and the morbidity and mortality from adenocarcinoma of the bowel i n women, these findings may have potentially important public health i mplications,.