Comorbidity As a Mediator of Survival Disparity Between Younger and Older Women Diagnosed with Metastatic Breast Cancer

The presence of comorbidity becomes increasingly important for its prognostic effect on survival in breast cancer patients with advancing age. This study aimed to evaluate the role of comorbidities including hypertension as a mediator of disparity in survival after metastasis diagnosis between younger (≤51 years) and older (>51 years) patients. A total of 553 patients 26-88 years of age with breast cancer metastasis diagnosis from 1 large urban practice were followed between January 1, 1999, and June 30, 2008. Comorbidity variables and survival were analyzed using Cox regression model. To assess comorbidity variables as a mediator of age-survival relationship, 2 approaches have been applied: (1) Baron Kenny approach and (2) alternative assessment to compute the percentage change in the hazard ratios (HRs). The median survival was 40 months, with 265 (47.9%) alive and 288 (52.1%) dead. Older patients had worse survival than younger patients (HR, 1.43; 95% confidence interval [CI], 1.11-1.84). Hypertension was related to survival (HR, 1.45; 95% CI, 1.12-1.89) when age and other covariates were controlled. The effect of age on survival was no longer significant after adjustment for hypertension (HR, 1.26; 95%, CI 0.97-1.65) or hypertension-augmented Charlson comorbidity score (HR, 1.24; 95% CI, 0.95-1.63). Hypertension-augmented Charlson comorbidity score or hypertension was a strong mediator of age-survival relationship among metastatic breast cancer patients, explaining survival disparity between younger and older patients by 44% and 40%, respectively. The study findings suggest that hypertension should be included in the comorbidity information for decision-making support programs.