Second primary cancer in breast cancer survivors by race/ethnicity and Asian subgroups: a descriptive epidemiologic...

Treatment advances have improved breast cancer survival, resulting in a growing population at risk for second primary cancers (SPCs). Although prior studies suggest racial heterogeneity in SPC risk, little is known about SPC patterns among diverse Asian American subgroups. Post-SPC survival outcomes by race/ethnicity and Asian subgroups remain underexplored.

We identified women with stages I-III breast cancer diagnosed between 2010 and 2020 in Surveillance, Epidemiology, and End Results. Primary outcomes included cumulative SPC incidence and post-SPC survival, stratified by race/ethnicity (Asian, Black, Hispanic, Pacific Islander, and White) and Asian subgroups (Chinese, Filipino, Indian/Pakistani, Japanese, Korean, Vietnamese). Cox models assessed the association between SPC and overall survival, treating SPC as a time-varying covariate to address immortal time bias.

Among 430 823 survivors, 5-year SPC incidence was highest in White (6.2% [95% CI = 6.1 to 6.3]) and lowest in Pacific Islander survivors (4.2% [95% CI = 3.7 to 4.7]). Disaggregating Asian subgroups revealed notable heterogeneity: Chinese survivors had the highest incidence (5.4% [95% CI = 4.8 to 6.1]) and Indian/Pakistani survivors the lowest (3.7% [95% CI = 2.9 to 4.4]). Second primary cancer development was associated with increased risk of mortality (adjusted hazard ratio [aHR] = 3.85 [95% CI = 3.73 to 3.98]). The magnitude of this association was most pronounced among Pacific Islander (aHR = 5.85) and least among White survivors (aHR = 3.68; interaction P < .001). Within Asian subgroups, the effect was strongest in Vietnamese (aHR = 7.93) and attenuated in Korean survivors (aHR = 3.45; interaction P = .13).

White and Chinese survivors had the highest SPC risk, while Pacific Islander and Vietnamese survivors faced greater mortality impact from SPCs. Racially disaggregated analyses revealed heterogeneity, underscoring the need for tailored care in the diverse US breast cancer survivor population.