Associations between weight in early adulthood, change in weight and breast cancer risk in postmenopausal women

Krishnan K, Bassett JK, Macinnis RJ, English DR, Hopper JL, McLean CA, Giles GG, Baglietto L (2013) Associations between weight in early adulthood, change in weight and breast cancer risk in postmenopausal women. Cancer Epidemiol Biomarkers Prev 22:1409-1416

BACKGROUND: Adult weight is positively associated with postmenopausal breast cancer but few studies have investigated whether there are associations with weight and body mass index (BMI) in early adulthood, or subsequent weight change. METHODS: 14,441 postmenopausal women from the Melbourne Collaborative Cohort Study were followed for 16.5 years (mean) and 668 incident breast cancers were identified. Hazard ratios (HRs) were estimated using Cox regression. RESULTS: Weight and BMI at 18-21 years were not associated with risk of any type of breast cancer and there was no variation by age. Women with the greatest increase in weight and BMI had higher risk at older ages (HR per 5 kg/m2 gain in BMI=1.24; 95% CI, 1.11-1.40) although the test for homogeneity by age was not significant. At older ages the association was stronger for PR positive disease compared with PR negative disease (HR per 5 kg/m2 gain in BMI, 1.43; 95% CI, 1.23-1.66; test for homogeneity by PR status, p<0.01). hrs="" were="" also="" greater="" for="" her2-="" and="" luminal="" a="" tumours,="" but="" the="" p-values="" for="" homogeneity="" by="" tumour="" subgroups="" were="" not="" significant.="" conclusion:="" early="" adulthood="" weight="" is="" not="" associated="" with="" risk="" of="" postmenopausal="" breast="" cancer.="" greater="" weight="" gain="" during="" adulthood="" might="" be="" associated="" with="" increased="" risk="" for="" older="" women="" (="">69 years) and this association might vary by tumour hormone receptor status. IMPACT: Further studies need to investigate the impact of increase in weight during adulthood on postmenopausal breast cancer risk and the potential variation by age or tumour characteristics.