Components of metabolic syndrome and risk of breast cancer by prognostic features in the study of osteoporotic fractures cohort.

Purpose: Metabolic syndrome (MetS) and most of its components have been previously associated with increased breast cancer risk. We hypothesized that increasing number of MetS components would be positively associated with breast cancer risk.

Methods: Data were obtained from the Study of Osteoporotic Fractures, a prospective cohort of women aged ≥65 enrolled between 1986 and 1988 and still being followed prospectively (n = 8,956). MetS components evaluated at baseline were elevated waist circumference, hypertension, and diabetes. Data were not available on hyperlipidemia. Incident breast cancers were confirmed by pathology report. We compared women with 0, 1, and 2 or 3 MetS components. We used Cox proportional hazards regression to calculate associations for breast cancer overall and classified by prognostic features.

Results: At baseline, 28.8 % of participants had 2 or 3 MetS components. Over an average follow-up of 14.4 years, 551 breast cancer cases were identified. Compared to those with no components, women with 2 or 3 components had increased breast cancer risk (hazard ratio (HR), 1.30; 95 % confidence interval (CI), 1.01-1.68) and increased risk of ER+ (HR, 1.48; 95 % CI, 1.09-2.03) and PR+ (HR, 1.56; 95 % CI, 1.10-2.20) cancer, adjusting for age, hormone use, and family history of breast cancer. These results became attenuated and not statistically significant when additionally adjusted for body mass index.

Conclusions: MetS is associated with increased postmenopausal breast cancer risk, especially for ER+ and PR+ cancers, though this effect may not be independent of the effect of body mass index. Managing the components of MetS could be efficacious for breast cancer risk reduction.