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The Effect of Stage at Diagnosis on the Association Between Race/Ethnicity and Survival in Patients with Primary Breast Cancer
Introduction: Breast cancer is the most common non-skin cancer in women in the United States. Minority groups such as Hispanics and Blacks generally have worse outcomes compared to the general population even after accounting for potential confounders. We hypothesize that stage at diagnosis modifies the magnitude of the disparities in survival seen in different racial/ethnic groups.
Objective: To assess if breast cancer survival is associated with race/ethnicity defined as Non-Hispanic Whites (NHW), Non-Hispanic Blacks (NHB), Hispanic Whites (HW), and Hispanic Blacks (HB), and whether this association is modified by stage at diagnosis.
Methods: A historical cohort, including breast cancer cases in Hispanic and non-Hispanic black and white women was assembled using the Surveillance, Epidemiology, and End Results (SEER) Database 2000-2019. Kaplan-Meier survival functions for each race/ethnicity were compared using the log rank test. Using multivariable Cox regression analysis, hazard ratios for cancer mortality for each race/ethnicity group were estimated while testing for the interaction between race/ethnicity and stage at diagnosis (localized, regional, and distant) and controlling for potential confounders.
Results: The study included 820,748 women 20 years or older with primary breast cancer. The 95-percentile survival time was 27, 25, 19 and 14 months for NHW, HW, HB and NHB respectively. As compared to NHW, HR (95%CI) in localized tumors were: NHB 1.57(1.50-1.65); HB 1.43(1.02-2.01); HW 1.05(0.99-1.11); In regional tumors NHB 1.50(1.45-1.54); HB 1.39(1.12-1.71); HW 1.11(1.07-1.15) and in distant tumors NHB 1.36(1.31-1.42); HB 1.16(0.89-1.50); HW 1.36(1.31-1.42).
Discussion/Conclusions: The study found that the association between race/ethnicity and breast cancer survival is indeed modified by stage at diagnosis. Compared to NHW, both HB and NHB have worse survival, and such differences in survival decrease as the stage at diagnosis is more advanced. Disparities in survival between HW and NHW are only evident in non-local tumors. Further research should clarify the role of biological vs. social factors in these disparities.