Differences in breast cancer survival across Asian American ethnicities compared with non-Latina White females in Kaiser Permanente Northern California

BACKGROUND: In the US, Asian American females with breast cancer have better survival than other groups, and survival differs across Asian American ethnicities. Reasons remain unclear. METHODS: We compared the survival of 5294 Asian American ethnicities and 5294 non-Latina White (NLW) females with incident stage I-IV breast cancer (2000-2015) in Kaiser Permanente Northern California. With follow-up through December 31, 2020, survival analysis was conducted using cause-specific Cox proportional hazards models adjusting for sociodemographic, clinical, treatment, social environment, and lifestyle factors. Overall, 1048 deaths (581 breast cancer-related) occurred in Asian American females and 1673 deaths (779 breast cancer-related) in NLW females. RESULTS: Compared with NLW females, Asian American females were younger (median = 56.2 vs. 63.0 years), lived in the highest socioeconomic status neighborhoods (Quintiles 4/5 = 57.7% vs. 50.3%), had fewer comorbidities (45.2% vs. 35.9% with zero), had a lower body mass index (BMI) (median = 24.8 vs. 27.4 kg/m2), and never smoked (47.2% vs. 26.9%), varying by Asian American ethnicity. All-cause mortality was lower in Asian American than NLW females (hazard ratio [HR] = 0.82; 95% CI = 0.74 to 0.91). Chinese (HR = 0.84; 95% CI = 0.70 to 1.00), Japanese (HR = 0.69; 95% CI = 0.55 to 0.88), and South Asian (HR = 0.73; 95% CI = 0.53 to 0.99) females had persistent survival advantages over NLW females. Adjusting for BMI and smoking attenuated associations. For breast cancer-specific mortality, associations were similar, though statistically non-significant. CONCLUSIONS: Asian American females-especially those of Chinese, Japanese, and South Asian descent-had better survival than non-Latina NLW females. Disaggregating Asian American ethnicities clarifies survival differences and may inform research on personal, social, and lifestyle factors to benefit all patients.