Mind the gap: racial differences in breast cancer incidence and biologic phenotype, but not stage, among low-income women participating in a government-funded screening program

Abstract

Breast cancer mortality rates in South Carolina (SC) are 40 % higher among African-American (AA) than European-American (EA) women. Proposed reasons include race-associated variations in care and/or tumor characteristics, which may be subject to income effects. We evaluated race-associated differences in tumor biologic phenotype and stage among low-income participants in a government-funded screening program. Best Chance Network (BCN) data were linked with the SC Central Cancer Registry. Characteristics of breast cancers diagnosed in BCN participants aged 47-64 years during 1996-2006 were abstracted. Race-specific case proportions and incidence rates based on estrogen receptor (ER) status and histologic grade were estimated. Among 33,880 low-income women accessing BCN services, repeat breast cancer screening utilization was poor, especially among EAs. Proportionally, stage at diagnosis did not differ by race (607 cancers, 53 % among AAs), with about 40 % advanced stage. Compared to EAs, invasive tumors in AAs were 67 % more likely (proportions) to be of poor-prognosis phenotype (both ER-negative and high-grade); this was more a result of the 46 % lesser AA incidence (rates) of better-prognosis (ER+ lower-grade) cancer than the 32 % greater incidence of poor-prognosis disease (p values <0.01). When compared to the general SC population, racial disparities in poor-prognostic features within the BCN population were attenuated; this was due to more frequent adverse tumor features in EAs rather than improvements for AAs. Among low-income women in SC, closing the breast cancer racial and income mortality gaps will require improved early diagnosis, addressing causes of racial differences in tumor biology, and improved care for cancers of poor-prognosis biology.

Fig. 1. Race-associated differences in invasive breast cancer biologic phenotypes

a,b: Within the BCN, case proportions (a) and age-adjusted incidence rates (b) demonstrate different perspectives on racial disparities. Rates are cases per 100,000 person-years-at-risk over ages 47–64. Asterisks indicate statistical significance of race-group comparisons for specific breast cancer phenotypic subtypes: * = p<0.05; ** = p<0.01. c: Proportional subtype incidence rates are race-specific, proportional to the total European-American invasive breast cancer incidence rate within each population (BCN or state-level). Gaps in the bars for African-Americans, between ER positive and ER negative subtypes, represent race-associated differences in total incidence within each population. Lines indicate differences in ER positive and ER negative proportions: solid lines for race-associated differences within each population, long-dashed lines for differences between African-Americans in the two populations, and short-dashed dashed lines for differences between European-Americans in the two populations. AA = African-American; EA = European-American; ER = estrogen receptor; G = histologic grade;