Large body size has been associated with decreased risk of breast cancer in premenopausal, but with increased risk in postmenopausal women. Limited information is available about African American women and differences by estrogen- and progesterone-receptor (ERPR) status.
We analyzed data from the Women's Contraceptive and Reproductive Experiences (CARE) Study among 3,997 white and African American breast cancer case patients diagnosed in 1994-98 and 4,041 control participants aged 35 to 64. We calculated multivariate odds ratios (ORs) as measures of relative risk of breast cancer associated with self-reported body mass index (BMI) at age 18 and 5 years before diagnosis (recent BMI).
Risk tended to decrease with increasing BMI at age 18 in all women (ORBMI≥25 kg/m2 vs <20kg/m2=0.76, 95% CI:0.63–0.90, Ptrend=0.005) and with recent BMI in premenopausal women (ORBMI ≥35 kg/m2 vs <25kg/m2=0.81, 95% CI:0.61–1.06, Ptrend=0.05), unmodified by race. Among postmenopausal white but not African American women, there was an inverse relation between recent BMI and risk. High recent BMI was associated with increased risk of ERPR positive tumors among postmenopausal African American women (ORBMI ≥35 kg/m2 vs <25kg/m2=1.83, 95% CI:1.08–3.09, Ptrend=0.03).
Among women at age 35-64, BMI at age 18 is inversely associated with risk of breast cancer, but association with recent BMI varies by menopause status, race and hormone receptor status.
Our findings indicate that studies of BMI and breast cancer should consider breast cancer subtypes.