Racial/ethnic and geographic differences in second primary cancers in stomach cancer survivors: a comparative study...

Stomach cancer remains the fifth leading cause of cancer death, with racial/ethnic and geographic differences. As survival improves, these survivors face elevated risks of second primary cancers (SPCs). We evaluated SPC risk and post-SPC survival by race/ethnicity and between the U.S. and South Korea.

We analyzed patients with stage I-III stomach cancer (2012-2020) from the U.S. SEER-17 and Korea Cancer Public-Library Database. SPCs were defined as non-gastric cancers diagnosed > 1 year post initial diagnosis. Cumulative SPC incidence was estimated using Aalen-Johansen method to account for competing death. Cox regression assessed survival impact of SPC development.

Among 19,595 U.S. and 204,240 Korean patients, 1,050 and 6,908 developed SPCs, respectively. In the U.S., 5-year SPC incidence was highest in Black (7.4% [6.1-8.6]) and lowest in Pacific Islanders (4.5% [2.3-6.7]). Notable heterogeneity in SPC incidence was observed across Asian subgroups, with Korean Americans showing the highest (6.9% [4.7-9.1]) and Filipinos the lowest (4.4% [1.9-7.2]). In contrast, Korean survivors in South Korea had the lowest SPC incidence (3.8% [3.7-3.9]). SPC development was associated with higher mortality (HR = 2.22 [1.96-2.52]), with a stronger effect in Asians (HR = 3.12) than Whites (HR = 1.96; interaction P < 0.1). Among Asian subgroups, SPC development was associated with the highest mortality in Vietnamese (HR = 13.6) and the lowest in Filipino survivors (HR = 1.54; interaction P < 0.01). Among Korean survivors in South Korea, SPC development conferred a modest increase in mortality risk (HR = 1.68 [1.61-1.75]).

SPC risk and outcomes in stomach cancer survivors vary by race/ethnicity and country, particularly within Asian subgroups.