Breast feeding practices in relation to endometrial cancer risk, USA

Objective: Breast feeding is associated with reduced estrogen, a profile that should be associated with decreased endometrial cancer incidence. We analyzed data from a population-based case-control study of Wisconsin women to evaluate the relation between lactation and endometrial cancer risk. Methods: Cases (n = 586) were identified from a statewide tumor registry; controls (n = 1653) were selected randomly from driver's license lists and Medicare beneficiary files. Breast feeding practices and other factors were ascertained by telephone interview. Results: Compared with parous women who did not breast feed, the multivariate relative risk for women who breast fed for at least 2 weeks was 0.90 [95% confidence interval (CI) 0.72-1.13]; increasing duration was not strongly associated with risk of disease (p for trend 0.4). More recent breast feeding was associated with significantly reduced risks. The relative risk for lactation within the recent three decades was 0.58 (95% CI 0.36-0.96) and for first breast feeding at age 30 or greater was 0.50 (95% CI 0.28-0.90). There was a suggestion that risk was increased in women who used lactation suppressant hormones - usually estrogens - more recently (p = 0.1) or at a later age (p = 0.1). Conclusions: This study suggests that, like breast cancer, endometrial cancer is modestly inversely associated with lactation.