Impact of Acquired Comorbidities on All-Cause Mortality Rates Among Older Breast Cancer Survivors

Background: Breast cancer survivors with higher numbers of morbidities at the time of primary treatment suffer higher rates all-cause mortality than comparatively healthier survivors. The c feet of time-varying comorbidity status on mortality in breast survivors, however, has not been well investigated. Objective: We examined longitudinal comorbidity in a cohort women treated for primary breast cancer to determine accounting for comorbidities acquired after baseline influenced the hazard ratio of all-cause mortality compared with an analysis using only baseline comorbidity. Methods: Cox proportional hazards adjusted for age, race/ethnicity, and exercise habits were modeled using (1) only a baseline Charlson index; (2) 4 Charlson index values collected longitudinally entered as time-varying covariates, with missing values addressed by carrying forward the prior observation; and (3) the 4 longitudinal Charlson scores entered as time-varying covariates, with values multiply imputed. Results: The 3 modeling strategies yielded similar results; Model 1 HR: 1.4 per unit increase in Charlson index, 95% confidence interval (CI): 1.2-1.7; Model 2 HR: 1.3, 95% CI: 1.1-1.5; and Model 3 HR: 1.4, 95% CI: 1.2-1.6. Conclusions: Our findings indicate that a unit increase in Charlson comorbidity index raises the hazard rate for mortality by approximately 1.4-fold in older women treated primary breast cancer. The conclusion is essentially the whether accounting only for baseline comorbidity or accounting acquired comorbidity over a median follow-up period of 85 months.