Postmenopausal overweight and breast cancer risk; results from the KARMA cohort

Abstract

PurposeTo study the risk of incident breast cancer and subtype-specific breast cancer in relation to excess body weight in a contemporary Swedish prospective cohort study, The Karolinska Mammography Project for Risk Prediction of Breast Cancer, KARMA.MethodsA total of 35,412 postmenopausal women attending mammography and included in the KARMA study provided baseline data on body mass index (BMI) and potential confounders. During eight years of follow-up, 822 incident invasive breast cancer cases were identified.ResultsWomen with overweight (BMI ≥ 25–< 30 kg/m2) constituting 34% of the study cohort had an increased risk of incident breast cancer with an adjusted Hazard Ratio (HRadj) 1.19 (95% CI 1.01–1.4). A similar, however, non-significant, association was found for women with obesity (BMI ≥ 30 kg/m2) conferring 13% of the cohort, with a HRadj of 1.19 (95% CI 0.94–1.5). Overweight was associated with risk of node-negative disease (HRadj 1.29, 95% CI 1.06–1.58), whereas obesity was associated with node-positive disease (HRadj 1.64, 95% CI 1.09–2.48). Both overweight and obesity were associated with risk of estrogen receptor positive (ER+) disease (HRadj 1.20, 95% CI 1.00–1.44 and HRadj 1.33, 95% CI 1.03–1.71, respectively), and low-grade tumors (HRadj 1.25, 95% CI 1.02–1.54, and HRadj 1.40, 95% CI 1.05–1.86, respectively). Finally, obesity was associated with ER+HER2 negative disease (HRadj 1.37, 95% CI 1.05–1.78) and similarly luminal A tumors (HRadj 1.43, 95% CI 1.02–2.01).ConclusionOverweight and obesity are associated with an increased risk of developing breast cancer, specifically ER+, low-grade, and for obesity, node-positive, high-risk breast cancer indicating a further need for risk communication and preventive programs.