28 March 2022
The role of obesity and weight change in breast-cancer development is complex and incompletely understood. Recently, Ellingjord-Dale et al.  recently reported the results of a study that investigated the effects of long-term weight change and the risk of breast-cancer risk taking into account body mass index (BMI) at 20 years of age, menopausal status, hormone replacement therapy (HRT) and hormone-receptor status. The authors used data related to weight collected at three different time points from women who participated in the European Prospective Investigation into Cancer and Nutrition (EPIC) study in order to analyze the association between weight change since age 20 up to mid-adulthood and risk of breast cancer. A total of 150,257 women (median age 51 years at cohort entry) were followed for a mean 14 years (standard deviation = 3.9) during which 6,532 breast-cancer cases occurred. In comparison to those with stable weight (± 2.5 kg), long-term weight gain of more than 10 kg was positively associated with postmenopausal breast-cancer risk in women who were lean at age 20 [hazard ratio (HR) = 1.42; 95% CI 1.22–1.65], were ever HRT users (HR = 1.23; 95% CI 1.04–1.44), never HRT users (HR = 1.40; 95% CI 1.16–1.68) and in estrogen and progesterone receptor positive (ER+PR+) breast cancer cases (HR = 1.46; 95% CI 1.15–1.85). The authors conclude that long-term weight gain was positively associated with postmenopausal breast cancer in women who were lean at age 20, both in HRT ever users and non-users, and hormone-receptor-positive breast cancer.