Abstract 3622: Racial disparities in second primary cancers in stomach cancer survivors: a comparative study of US and Korea cancer registries

Abstract Background: Stomach cancer shows racial disparities in incidence and mortality, influenced by biological, lifestyle, and healthcare factors globally. With improved survival rates, stomach cancer survivors face an elevated risk of second primary cancer (SPC). However, racial differences in SPC risk and post-SPC survival remain unclear. We examined these disparities, leveraging disaggregated racial data from the U.S. and Korea SEER Registries. Methods: Data from 47, 627 U.S. stomach cancer survivors (stage I-III, diagnosed 2000-2021, survival ≥1 year) were analyzed. SPCs were defined as primary cancers diagnosed >1 year after the initial stomach cancer. The cumulative SPC incidence (stomach vs. other SPCs) were estimated using the Aalen-Johansen estimator, accounting for competing death. Cox regression evaluated the impact of SPC development on overall survival by treating SPC as a time-varying factor. Comparative analysis included 200, 456 stomach cancer survivors in Korea (2012-2020). Results: Among 47, 627 U.S. stomach cancer survivors (49% localized-stage), 4, 918 developed SPC (996 stomach SPC and 3, 911 non-stomach SPC) over 238, 135 person-years. The cumulative incidence of stomach SPC increased over time, with Hispanic survivors having the highest 15-year incidence (3.6%, CI: 3.1-3.6%). While grouped Asian data suggested a moderate stomach SPC incidence (3.0% CI: 2.4-3.5), disaggregated analysis revealed heterogeneity (1.4%-3.3%), highest in Korean and lowest in Filipino survivors. The cumulative incidence of non-stomach SPC, however, showed less variability among Asian subgroups. Survival analysis found that any SPC development (vs. those without SPC) was associated with 2.2 (CI: 2.07-2.29) times higher mortality risk. In race-specific subgroup analyses, the mortality impact of SPC development was more pronounced in Asians (adjusted hazard ratio, HR=3.2) vs. in Whites (HR=1.9; Interaction P<.1). Among Asian subgroups, the mortality impact of SPC was highest in Koreans and Chinese (HR=3.5 vs. 1.8 in Filipinos). Data from the Korean SEER Registry, including 200, 456 survivors (75.1% localized stage [vs. 50.7% in Korean Americans]), showed that SPC incidence was half of that observed in Korean American patients. The post-SPC mortality risk was lower in Korea (HR: 2.0) than in Korean Americans in the US (HR: 3.49). Conclusions: SPC incidence and post-SPC survival in stomach cancer survivors vary by race, with marked heterogeneity among disaggregated Asian subgroups. Patient groups with a better prognosis from initial stomach cancer, such as Asians and Koreans, experience a higher incidence of SPC and greater post-SPC mortality, possibly due to the longer survival time allowing for SPC development. Comparative studies linking US and Korean SEER with claims data could advance understanding of SPC patterns and post-treatment surveillance outcomes. Citation Format: Yuntong Wang, Dong-Woo Choi, Minjin Kim, Jialin Mao, Art Sedrakyan, Kui Son Choi, Heejung Chae, Eunji Choi. Racial disparities in second primary cancers in stomach cancer survivors: a comparative study of US and Korea cancer registries [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 3622.