Background: Comorbidities have been suggested influencing mammography use and breast cancer stage at diagnosis. We compared mammography use, and overall and advanced-stage breast cancer rates, among female Medicare beneficiaries with different levels of comorbidity. Methods: We used linked Breast Cancer Surveillance Consortium (BCSC) and Medicare claims data from 1998 through 2006 to ascertain comorbidities among 149,045 female Medicare beneficiaries ages 67 and older who had mammography. We defined comorbidities as either "unstable" (life-threatening or difficult to control) or "stable" (age-related with potential to affect daily activity) on the basis of claims within 2 years before each mammogram. Results: Having undergone two mammograms within 30 months was more common in women with stable comorbidities (86%) than in those with unstable (80.3%) or no (80.9%) comorbidities. Overall rates of advancedstage breast cancer were lower among women with no comorbidities [0.5 per 1,000 mammograms, 95% confidence interval (CI), 0.3-0.8] than among those with stable comorbidities (0.8; 95% CI, 0.7-0.9; P = 0.065 compared with no comorbidities) or unstable comorbidities (1.1; 95% CI, 0.9-1.3; P = 0.002 compared with no comorbidities). Among women having undergone two mammograms within 4 to 18 months, those with unstable and stable comorbidities had significantly higher advanced cancer rates than those with no comorbidities (P = 0.004 and P = 0.03, respectively). Conclusions: Comorbidities were associated with more frequent use of mammography but also higher risk of advanced-stage disease at diagnosis among the subset of women who had the most frequent use of mammography. Impact: Future studies need to examine whether specific comorbidities affect clinical progression of breast cancer.
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