Postmenopausal estrogen use and invasive versus in situ breast cancer risk

To examine the effect of cancer histopathology on the relationship between estrogen-replacement therapy (ERT) use and breast cancer risk, we performed a case control study of 109 postmenopausal women 45 years or older with in situ or invasive breast cancer matched to 545 controls. When in situ and i nvasive tumors were combined, the overall odds ratio (OR) describing the as sociation between ERT use and breast cancer risk was not statistically sign ificantly elevated (adjusted OR = 1.48, 95% confidence interval [CI] = 0.89 -2.47). When the analyses were confined to women with invasive disease, ris k estimates were uniformly higher (adjusted OR = 1.85, 95% CI = 1.00-3.45). In contrast, the overall estimate for the relationship between ERT use and in situ breast cancer was close to 1 (adjusted OR = 1.08, 95% CI = 0.42-2. 77). The positive association between ERT use and invasive breast cancer we observed, and the lack of association in women with in situ disease, may r epresent a distinct biological difference or may be related to the small sa mple size of our study. I CLIN EPIDEMIOL 51;12:1277-1283, 1998. (C) 1998 El sevier Science Inc.