Adult weight gain and histopathologic characteristics of breast cancer among postmenopausal women

BACKGROUND. Although the link between postmenopausal breast cancer and adiposity is well established, the association between weight gain and specific histopathologic characteristics of breast carcinoma has not been studied carefully. METHODS. Using 1200 incident invasive breast cancers among 44,161 postmenopausal women who were not taking hormone therapy in the American Cancer Society's Cancer Prevention Study II Nutrition Cohort, the authors computed age-adjusted rates and rate ratios (BR) for breast cancer by histology, stage, grade, and estrogen receptor (ER) and progesterone receptor (PR) status by categories of adult weight gain. RESULTS. Age-adjusted rates of breast cancer were highest for women who reported the most weight gain, regardless of histologic type. For weight gain > 60 pounds, compared with weight gain <= 20 pounds the RR for ductal carcinoma was 1.89 (95% confidence interval [95% CI], 1.53-2.34), and the RR for lobular carcinoma was 1.54 (95% CI. 1.01-2.33). Weight gain was associated with increased risk at every tumor stage and grade. The risk for regional or distant stage was elevated significantly in every category of weight gain and was 3 times higher among women who had the greatest weight gain (RR, 3.15; 95% CI, 2.21-4.48). Weight gain was associated with increased risk of ER-positive/PR-positive tumors (P for trend <.0001) but not ER-negative/PR-negative tumors (P for trend =.09). The results essentially remained unchanged when the analysis was restricted to women who had regular screening mammograms. CONCLUSIONS. Excess adiposity is an important contributor to breast cancer risk among postmenopausal women, regardless of histologic type, and especially for tumors of advanced stage and high grade.