Diabetes and other comorbidities in breast cancer survival by race/ethnicity: The California Breast Cancer Survivorship Consortium (CBCSC)

Background:The role of comorbidities in survival of breast cancer patients has not been well studied, particularly in non-white populations. Methods:We investigated the association of specific comorbidities with mortality in a multiethnic cohort of 8,952 breast cancer cases within the California Breast Cancer Survivorship Consortium (CBCSC), which pooled questionnaire and cancer registry data from five California-based studies. In total, 2,187 deaths (1,122 from breast cancer) were observed through December 31, 2010. Using multivariable Cox proportional hazards regression, we estimated hazards ratios (HR) and 95% confidence intervals (CI) for overall and breast cancer-specific mortality associated with previous cancer, diabetes, high blood pressure (HBP), and myocardial infarction (MI). Results:Risk of breast cancer-specific mortality increased among breast cancer cases with a history of diabetes (HR=1.48, 95% CI=1.18, 1.87) or MI (HR=1.94, 95% CI=1.27-2.97). Risk patterns were similar across race/ethnicity (non-Latina White, Latina, African American and Asian American), body size, menopausal status, and stage at diagnosis. In subgroup analyses, risk of breast cancer-specific mortality was significantly elevated among cases with diabetes who received neither radiation nor chemotherapy (HR=2.11, 95% CI=1.32-3.36); no increased risk was observed among those who received both treatments (HR=1.13, 95% CI= 0.70-1.84) (P interaction= 0.03). A similar pattern was found for MI by radiation and chemotherapy (P interaction=0.09). Conclusion:These results may inform future treatment guidelines for breast cancer patients with a history of diabetes or MI. Impact:Given the growing number of breast cancer survivors worldwide, we need to better understand how comorbidities may adversely affect treatment decisions and ultimately outcome.