The Influence of Medical Comorbidities on Survival Disparities in a Multiethnic Group of Patients with De Novo Metastatic Breast Cancer.

Background: The influence of common medical comorbidities on mortality and racial/ethnic disparities in mortality among women with metastatic breast cancer remains largely unknown.

Methods: In this longitudinal study, women with newly diagnosed stage IV breast cancer were identified in a large, diverse, integrated healthcare delivery system from January 2009 to December 2017 (n = 995) and followed through December 31, 2018, for all-cause (overall) and breast cancer-specific mortality via electronic health records. We computed overall and breast cancer-specific mortality rates by race/ethnicity and Elixhauser comorbidity index (ECI). Multivariable-adjusted hazard ratios (HR) assessing the influence of race/ethnicity and comorbidity status on overall and breast cancer-specific mortality were estimated using proportional hazards regression adjusted for age, breast cancer subtype, geocoded income, and palliative cancer treatments.

Results: Nearly 17% of this cohort had diabetes and 45% had hypertension. Overall, 644 deaths occurred in the cohort (median follow-up time of 1.8 years), of which 88% were breast cancer related. The risk of overall mortality was increased in Asian/Pacific Islander (PI; adjusted HR = 1.45; 95% CI, 1.10-1.92) and African American/Black women (adjusted HR = 1.34; 95% CI, 1.02-1.76) when compared with white women. Women with more comorbidities (ECI ≥ 5) had more than 3-fold higher overall mortality rate than those without any comorbidities [602/1,000 person-year (PY) vs. 175/1,000 PY]. Similar associations were found for breast cancer-specific mortality.

Conclusions: Medical comorbidities are associated with an increased risk of overall mortality among women with de novo metastatic disease and may influence racial/ethnic disparities in mortality.

Impact: Optimizing the management of medical comorbidities in metastatic breast cancer patients may also help reduce disparities in breast cancer-related mortality.