PROSPECTIVE-STUDY OF RELATIVE WEIGHT AND RISK OF BREAST-CANCER - THE BREAST-CANCER DETECTION DEMONSTRATION PROJECT FOLLOW-UP-STUDY, 1979 TO1987-1989

Despite extensive research on obesity and breast cancer in recent deca des, inconsistencies in the literature exist. The authors examined pro spectively the relation between adult relative weight (weight (kg)/hei ght (m)(1.5)) and breast cancer risk in a cohort of 54,896 women aged 31-89 years who had previously participated in the Breast Cancer Detec tion Demonstration Project, During a mean follow-up period of 7 years, 226 of the premenopausal women and 1,198 of the postmenopausal women developed breast cancer, Analysis was performed using Cox proportional hazards regression methods with age as the underlying time variable a nd adjusted for the effects of potential confounders, Among postmenopa usal women, the risk of breast cancer increased with increasing relati ve weight (p < 0.05 for trend); relative risk for the highest compared with the lowest quintile for relative weight was 1.3 (95% confidence interval (CI) 1.1-1.6), This association was modified by age at diagno sis, with relative risks of 1.1 (95% CI 0.8-1.4), 1.2 (95% CI 0.8-1.7) , and 1.8 (95% CI 1.3-2.5), respectively, for women aged <60, 60-64, a nd greater than or equal to 65 years, The higher risk of breast cancer among the older and overweight women was largely confined to women wh ose weights were measured during the postmenopausal but not the premen opausal period, This risk pattern was observed among the naturally men opausal women, but was also apparent in the smaller group of women wit h bilateral oophorectomy or hysterectomy with one ovary retained. Amon g premenopausal women, adult relative weight was not associated with b reast cancer risk. These findings suggest that the inconsistencies in the literature on obesity and breast cancer may be due in part to the differing age distributions of the populations studied. The authors co nclude that prevention of obesity throughout adulthood, particularly a fter menopause, may help reduce breast cancer among older women.