Race/Ethnicity and Changing US Socioeconomic Gradients in Breast Cancer Incidence: California and Massachusetts, 1978–2002 (United States)

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Abstract
Objective We tested the hypothesis that the US socioeconomic gradient in breast cancer incidence is declining, with the decline most pronounced among racial/ethnic groups with the highest incidence rates. Methods We geocoded the invasive incident breast cancer cases for three US population-based cancer registries covering: Los Angeles County, CA (1978–1982, 1988–1992, 1998–2002; n = 68,762 cases), the San Francisco Bay Area, CA (1978–1982, 1988–1992, 1998–2002; n = 37,210 cases) and Massachusetts (1988–1992, 1998–2002; n = 48,111 cases), linked the records to census tract area-based socioeconomic measures, and, for each socioeconomic stratum, computed average annual breast cancer incidence rates for the 5-year period straddling the 1980, 1990, and 2000 census, overall and by race/ethnicity and gender. Results Our findings indicate that the socioeconomic gradient in breast cancer incidence is: (a) relatively small (at most 1.2) and stable among US white non-Hispanic and black women; (b) sharper and generally increasing among Hispanic and Asian and Pacific Islander American women; and (c) cannot be meaningfully analyzed without considering effect modification by race/ethnicity and immigration. Conclusion Our results indicate that secular changes in US socioeconomic gradients in breast cancer incidence exist and vary by race/ethnicity.