This is a review of epidemiologic studies, which suggest that comorbidity (e.g., diabetes and heart disease) has an adverse effect on survival among women with incident, invasive breast cancer, adjusting for chronological age and stage of breast cancer at diagnosis. As part of this review, recent results are presented from a series of 463 breast cancer cases, identified through the Metropolitan Detroit Cancer Surveillance System. Women with two or more concurrent health conditions were 2.2 times more likely than breast cancer cases without comorbidity to die from their breast cancer over a four-year period (95% CI: 1.13, 4.18). Limiting heart disease was especially problematic. Recommendations are made for future research in this area.