Racial differences in the effects of comorbidity on breast cancer-specific survival

Purpose: In an effort to explain racial disparities in breast cancer survival, this study aimed to investigate how comorbidity affects breast cancer-specific mortality by race. Methods: A retrospective cohort study was conducted using the Surveillance, Epidemiology and End Results—Medicare linked data including 68,090 women 66+ years, who were diagnosed with stage I–III breast cancer in the United States from 1994 to 2004. Hospital and outpatient claims from the year prior to breast cancer diagnosis were used to identify comorbid conditions and patients were followed for survival through 2010. Results: Competing risk survival analysis failed to demonstrate any negative comorbidity effects on breast cancer-specific survival for black women. An increased breast cancer-specific mortality hazard was observed for white women who had diabetes without complication relative to white women without this condition after adjusting for age and year of diagnosis (hazard ratio: 1.22, 95% confidence interval 1.13, 1.30). The Cochran–Armitage Test showed diabetes was associated with a later stage of diagnosis (p < 0.01) and a more aggressive tumor grade (p < 0.01) among white women in the study population. Conclusion: Race specific comorbidity effects do not explain breast cancer-specific survival disparities. However, the relationship between diabetes and breast cancer, including the role of aggressive tumor characteristics, warrants special attention.