Cancer epidemiology, biomarkers & prevention : a publication of the American Association for Cancer Research, cosponsored by the American Society of Preventive Oncology 2017 01 13() pii cebp.0789.2016
Obesity has been more consistently associated with breast cancer than type 2 diabetes (T2D). This analysis examined the combination of the two factors in the Multiethnic Cohort (MEC).
Women aged 45-75 years entered the MEC in 1993-1996 by completing a questionnaire. T2D status was self-reported at baseline, two follow-up questionnaires, and confirmed by administrative data. Cancers were identified from tumor registries and deaths through vital records until 2010. Cox regression was applied to estimate hazard ratios (HR) and 95% confidence intervals (CI) for BMI and T2D status alone and in combination.
Among 103,721 (25,146 white, 20,255 African American, 7,681 Native Hawaiian, 28,012 Japanese American, 22,627 Latina) women with 14,558 T2D cases, 6,692 women developed breast cancer during 14.8±4.1 years of follow-up. T2D was significantly associated with breast cancer risk (HR, 1.15; 95%CI, 1.07-1.23), but including body mass index (BMI) lowered the HR to 1.08 (95%CI, 1.00-1.16). Ethnic-specific BMI-adjusted models showed elevated risks for T2D in Latinas only (HR, 1.30; 95%CI, 1.11-1.52). In contrast, obesity predicted statistically significant 21%-46% higher risks, after T2D adjustment, in all ethnic groups except Latinas (HR, 1.17; 95%CI, 0.99-1.38).
As reported previously, inclusion of BMI weakened the association of T2D with breast cancer. T2D status but not BMI was primarily associated with higher breast cancer risk in Latinas.
The role of obesity and T2D in breast cancer etiology may differ by ethnicity suggesting metabolic differences related to obesity.