Background: Breast cancer (BC) incidence rates reflect the interplay of biological, environmental, and social determinants of health. Uncertainty exists about the influence of community resource context and incidence of breast cancer by estrogen receptor (ER) status. We aimed to determine the association of community resource indices on incidence of breast cancers by ER status in Scotland, UK and USA.
Methods: We used cancer registry data from Scotland and US SEER, linked to validated composite community indices: Scottish Index of Multiple Deprivation (SIMD) and US Yost index, which characterize geographic areas across multiple domains including income, employment, education and housing. We analyzed 62,378 female invasive BCs diagnosed in Scotland (2000-2016) and 778,123 in USA (2006–2019). Average Annual Percentage Change (AAPC), age-standardized incidence rates (ASR) and 95% Confidence Intervals (CI) were calculated by ER status, and quintiles of SIMD Scotland and Yost Index linked to census tracts in USA. Q5 were the higher resourced communities and Q1 the lowest. USA analyses were stratified by race and ethnicity and for this presentation focused on the four largest groups: non-Hispanic White (NHW), non-Hispanic Black (NHB), Hispanic, Asian and Pacific Islander (API) women.
Results: Screen-detected ER+ tumor incidence increased over time in Scotland, particularly in the highest quintile [AAPC= 2.9% with 95% CI from 1.2 to 4.7]. No marked differences were observed for non-screen-detected ER+ tumors or ER- tumors by SIMD. In the USA there was considerable variation in AAPC by Yost index and ER status: for ER+ tumors, AAPCs were highest for API in the middle-resourced category (Yost Q3) with [AAPC=2.43% with 95% CI from 1.8 to 3.0]  and lowest for NHW in the least resourced Yost quintile. ER- tumor AAPCs showed declines across all Yost quintiles among all racial and ethnic groups. ASRs were highest for ER+ tumors among the most resourced communities of NHW women [Q5 ASR₂₀₀₆=199.27 ASR₂₀₁₉=212.93 AAPC=0.40 (95%CI=0.2 to 0.6)]; NHW women in the lowest Yost quintile had ~40% lower ER+ tumor rates [Q1 ASR₂₀₀₆=144.14 ASR₂₀₁₉=152.73 AAPC=0.65 (95%CI=0.3 to 0.9)] compared to the highest Yost quintile,. Higher ER+ rates were observed among the most resourced communities compared to least resourced Yost quintile areas for all racial and ethnic groups. Rates for ER- tumors did not differ by Yost quintiles for any racial and ethnic groups. NHB women had the highest ER- rates regardless of Yost index [NHB Q1 ASR₂₀₀₆=67.74, ASR₂₀₁₉=60.38 AAPC=0.40 (95%CI=0.2 to 0.6) and NHB Q5 ASR₂₀₀₆=64.28, ASR₂₀₁₉=48.66, AAPC=-3.53 (95%CI=-4.6 to -2.5)], which was 60-80% higher than NHW depending on the Yost quintile.
Conclusion: Communities with increased resources had higher incidence of ER+ tumors but not ER- tumors in Scotland and USA, supporting etiologic heterogeneity. Community context does not likely explain the higher ER- rates seen among NHB women and the underlying etiologic factors associated with ER-negative breast cancer need identification. Studies should incorporate area-level community indices to further the molecular epidemiology of cancer and identify individual and external factors for targeted prevention efforts that would be most impactful in reducing disparities in cancer morbidity and mortality.