OBJECTIVES:

Poorer breast cancer (BC) prognosis has been strongly linked with lower socioeconomic position (SEP) and certain racial/ethnic groups. This study aims to determine whether area level socioeconomic position mediates racial/ethnic differences in BC recurrence risk among hormone receptor(HR+) and Human epidermal growth factor2 (HER2 -) negative BC patients.

METHODS:

This is a retrospective cohort study using the Surveillance, Epidemiology and End Results of women 18+ years diagnosed with stage I-III, HR+ HER2- BC from 2004-2015. The primary outcome is BC recurrence risk measured by high Oncotype DX recurrence score (ODX), a multigene prognostic tool for BC. An ODX score > 26 is defined as high. SEP is a composite index calculated using county-level education, income, poverty and unemployment census data. Mediation analysis was conducted using the product method to determine the association of SEP (mediator) with racial/ethnic differences in ODX score.

RESULTS:

A total of 87,556 women (mean [SD] age 57.7 [10.6] years) were included in the study. Higher proportion of NHB (20.9%), Non-Hispanic American Indian/Alaska Native (NHAIAN) (20.3%) and Hispanic (19%) women lived in neighborhoods classified in the lowest SEP quintile compared to NHW (10.8%) and Non-Hispanic Asian Pacific Islander (NHAPI) (5.7%). NHB women (OR, 1.34[ 95% CI, 1.25- 1.43]) and NHAIAN (OR, 1.35 [95%CI, 1.01-1.77]) women had higher odds of high ODX score compared to NHW women after adjusting for confounders. Race/ethnicity and odds of high ODX score changed only slightly [NHB: OR 1.33 (95% CI, 1.25- 1.43) and NHAIAN: OR, 1.34 (95% CI, 1.01- 1.76) after adjusting for SEP as a mediator. The proportion effect mediated by SEP was not statistically significant for all racial/ethnic groups with the exception of NHB patients (PM: 15%, 95% CI 5-29%).

CONCLUSIONS: In this study evaluating racial/ethnic disparities in BC recurrence risk, little evidence of mediation by county level SEP was observed.