Elucidating Determinants of Survival Disparities Among a Real-world Cohort of Metastatic Breast Cancer Patients: A...

Disparities in breast cancer survival by race/ethnicity and socioeconomic status have been reported. However, it is unclear if these findings are reproducible among subpopulations. This study aimed to assess if socially oriented factors are predictive of overall survival (OS) among patients with hormone receptor-positive (HR⁺), human epidermal growth factor 2-positive (HER2⁺) metastatic breast cancer (MBC).

We analyzed patients with MBC included in the National Cancer Database diagnosed with HR⁺ and HER2⁺ disease treated between 2010 and 2015. Multivariate analyses describe the association between non-clinical prognostic factors and OS. A matched analysis, which balanced prognostic factors between whites and African Americans (AA), was also conducted.

Of the 6200 patients analyzed, the majority were 50 years or older, white, and treated with hormonal therapy. Disparities in OS were observed; multivariate analysis revealed diminished survival was associated with low income (< $38K vs. ≥ $63K, hazard ratio [HR], 1.30; P < .001), having government insurance (government vs. private, HR, 1.55; P < .001), living closer to one's treatment facility (< 4 miles vs. ≥ 18 miles, HR, 1.16; P = .04), and being AA (AA vs. white, HR, 1.20; P = .006). The mortality disparity attributed to race was insignificant in the matched analysis (AA vs. white, HR, 1.13; 95% confidence interval, 0.98-1.30; P = .09).

This study confirms that the known sociodemographic disparities in OS among patients with MBC are similar within the HR⁺/HER2⁺ subpopulation. The discordance of outcomes between matched and unmatched analysis demonstrate that there is a highly vulnerable subgroup of AAs. Further investigation is required to determine if the identified associations are independently causal of poor prognosis.