Importance: In the US, breast cancer mortality is lower among Asian American females diagnosed with breast cancer compared with other racial and ethnic groups, although reasons for this difference are not well understood. Objective: To examine contributions of clinical, lifestyle, and sociodemographic factors to mortality differences among females identifying as Asian races and ethnicities compared with non-Latina White females and whether associations vary by nativity. Design, Setting, and Participants: This cohort study analyzed time-to-event survival data from Asian and White females with breast cancer from 4 epidemiologic studies. Cohorts were recruited from California and Hawaii, with information from questionnaires and cancer registries. Participants were females with first primary invasive breast cancer diagnosed from 1992 to 2019 who self-identified as Asian and females who self-identified as White as a comparison group. Analyses were conducted from February 2024 to February 2026. Exposures: Self-reported race and ethnicity, nativity, clinical factors (eg, stage and tumor grade), marital status, educational level, reproductive factors, insurance status, lifestyle factors (eg, smoking and alcohol use), diabetes, and neighborhood socioeconomic indicators. Main Outcomes and Measures: The outcomes of interest were all-cause and breast cancer-specific mortality. Cox proportional hazards models were used to estimate hazard ratios (HRs) comparing each Asian group with White females, and changes in these estimates with adjustment for various prognostic factors. Results: A total of 8994 females (mean SD age at diagnosis, 59 13 years), including 3973 Asian females and 5021 White females, were analyzed. There were 2637 total deaths and 1140 deaths attributed to breast cancer (mean follow-up time 12.6 years; range, 1 month to 28 years). Most Asian groups had a higher proportion diagnosed before age 50 years compared with White females: from 34% among Filipinas to 73% among another Asian group vs 15% among White females. Nearly all Asian ethnic groups had lower proportions (45%-67%) of localized stage disease relative to White females (69%). Relative to White females, risk of all-cause mortality in fully adjusted models was lower for Chinese females (HR, 0.77; 95% CI, 0.62-0.96), Filipina females (HR, 0.81; 95% CI, 0.67-0.99), Japanese females (HR, 0.71; 95% CI, 0.54-0.93), and Asian females identifying as multiple races or ethnicities, not Native Hawaiian or Pacific Islander (HR, 0.67; 95% CI, 0.51-0.89). Lower adjusted risk of all-cause mortality was observed for Chinese (HR, 0.73; 95% CI, 0.57-0.94) and Filipina (HR, 0.79; 95% CI, 0.63-0.94) females born outside the US and Japanese females (HR, 0.63; 95% CI, 0.45-0.90) and Asian females with multiple races or ethnicities, not Native Hawaiian or Pacific Islander (HR, 0.59; 95% CI, 0.39-0.88) born in the US compared with White females. Conclusions and Relevance: In this pooled cohort study of females with breast cancer, several Asian groups had lower risk of all-cause mortality, even after accounting for clinical, sociodemographic, reproductive, lifestyle, and neighborhood factors. Identification of the specific resiliency factors will provide insights into mechanisms that may improve survival after breast cancer.
Gomez et al. (Wed,) studied this question.