Impact of immigration factors on breast cancer mortality varies by stage at diagnosis among Northern California Hispanic women

Foreign-born Hispanics have lower breast cancer (BC) mortality rates than US-born Hispanics, despite lower socioeconomic status. However, few studies have explored the joint effects of individual- and neighborhood-level immigration factors, or the modifying effects of stage at diagnosis on this apparent paradox. We studied 1,739 Hispanic women diagnosed with invasive BC during 1995-2008 from two population-based studies in the San Francisco Bay Area. Information on nativity, generational status, and language preference was obtained by in-person interview; a neighborhood Hispanic enclave variable was derived from Census data. BC-specific mortality by AJCC stage was examined using Cox proportional hazards regression. Among patients diagnosed with stage III/IV disease, BC mortality was lower in foreign-born Hispanics (Hazard Ratio (HR) =0.49, 95% CI=0.26-0.92), first generation immigrants who spent <50% of their life in the US compared to third or higher generation Hispanics (HR=0.31, 95% CI=0.11-0.90), and women with Spanish language preference (HR=0.41, 95% CI=0.20-0.87). Among patients diagnosed with stage II disease, immigration factors were not associated with BC mortality. Among patients diagnosed with stage I disease, BC mortality was higher in first generation immigrants who spent <50% of their life in the US (HR=4.22, 95% CI=1.11-15.96); worse mortality was also seen in foreign-born Hispanics, and those with Spanish language preference. Residence in a Hispanic enclave was not associated with BC mortality. Our analysis showed that immigration factors are associated with BC mortality and these relationships are modified by stage at diagnosis. The Hispanic paradox on BC mortality was limited to women with stage III/IV disease.