Childbirth and Subsequent Risk of Breast Cancer: The Influence of Pregnancy, Placental, and Birth Characteristics. A Population-Based Swedish Study

摘要

Indirect markers of hormone exposures during pregnancy have inconsistently been associated with subsequent risk of breast cancer in the mother. The authors sought to examine associations between the weight of the placenta and birth weight and mother's breast cancer risk. This was a population-based cohort study that used data from the Swedish National Registers. Subjects were women who delivered single births between 1982 and 1989 in Sweden (n=314,019). In all, 2,216 women developed breast cancer during the followup period, which lasted through 2001. Compared to women with placentas weighing less than 500 grams in two consecutive pregnancies, the risk of breast cancer was increased among women whose placentas weighed 500-699 grams in the first pregnancy and at least 700 grams in the second pregnancy, or vice versa (adjusted hazard ratio 1.82; 95% confidence interval (CI) 1.07-3.08), and among women whose placentas weighed at least 700 grams in both pregnancies (adjusted hazard ratio 2.05; 95% CI 1.15-3.64). These results further support the hypothesis that pregnancy hormones are important modifiers of subsequent maternal breast cancer risk.