Survival Differences in Breast Cancer among Racial/Ethnic Groups: A Population-Based Study

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Abstract
In women, breast cancer is the most frequent solid tumor and the second leading cause of cancer death. Differences in survival of breast cancer have been noted among racial/ethnic groups, but the reasons are unclear. This report presents the characteristics and the survival experience of four racial/ethnic groups and evaluates the effects of stage, age, histology, and treatment on survival time. The distributions of prognostic factors and treatment among racial/ethnic groups are compared using female breast cancer patients from two population-based registries in Southern California. The main end points are observed survival time and survival by cause of death. The Cox model is used to estimate the relative risk of death in three minority groups compared with non-Hispanic whites, while controlling for several covariates. Breast cancer cases included in this study were 10,937 non-Hispanic whites, 185 blacks, 875 Hispanics, and 412 Asians. The median follow-up period was 76 months (range: 48-132). The median age at diagnosis was 64 years among non-Hispanic whites, 55 years among Hispanics (p = 0.001), 52 years among blacks (p = 0.001), and 50 years among Asians (p = 0. 001). There was more localized disease among non-Hispanic whites (61. 4%) than among blacks (50.8%) and Hispanics (52.2%), but not compared to Asians (59.7%). After controlling for stage, age, histology, treatment, and registry, overall survival significantly differed between non-Hispanic whites and blacks [relative risk (RR) = 2.27, 95% confidence interval (95% CI) 1.82-2.84) and between non-Hispanic whites and Hispanics (RR = 1.18, 95% CI 1.04-1.34). The same results were found for breast cancer death in blacks (RR = 2.32, 95% CI 1.76-3.07) and Hispanics (RR = 1.28, 95% CI 1.10-1.50). We found no difference between Asians and non-Hispanic whites in overall and cancer-related survival. These results show that stage of disease, age at diagnosis, histologic features and treatment for breast cancer differed among racial/ethnic groups. Moreover, black women, in particular, and Hispanic women with breast cancer had a higher risk of death compared to non-Hispanic white women, even after controlling for prognostic factors. These findings underline the necessity of improved screening and access to appropriate treatment among minority women for breast cancer.