Metabolic syndrome and incidence of breast cancer in middle-aged Korean women: a nationwide cohort study.

PURPOSE: To evaluate the risk of breast cancer in middle-aged women with metabolic syndrome using the National Health Insurance Service-National Sample Cohort (NHIS-NSC).

METHODS: We analyzed 23,820 women aged 50-64 years who participated in the NHIS-NCS in 2008 and 2009. We excluded subjects with any previous history of cancer or with inadequate information regarding metabolic syndrome. Participated subjects underwent anthropometric measurements and provided fasting blood samples for the assessment of glucose and lipid profiles, and answered a lifestyle questionnaire. Cox regression analysis was performed to evaluate relative risks (RRs) and 95% confidence intervals (CIs) for the association between metabolic syndrome and breast cancer.

RESULTS: During the 5-year follow-up, 131 subjects were newly diagnosed with breast cancer (incidence, 10.86 per 10,000 person years). After adjusting for age and body mass index, the RR for incident breast cancer in participants with metabolic syndrome versus those without it was 1.47 (95% CI 1.01-2.13). For those individuals of metabolic syndrome, hyperglycemia was most primarily related with the incidence of breast cancer (RR 1.44, 95% CI 1.02-2.04).

CONCLUSIONS: Among the study individuals who were middle-aged Korean women, metabolic syndrome is highly related with the risk of breast cancer. Therefore, it needs to be managed or prevented to reduce the incidence of breast cancer.