Nature versus nurture: the impact of nativity and site of treatment on survival for gastric cancer

Background: The prognosis of gastric cancer patients is better in Asia than in the West. Genetic, environmental, and treatment factors have all been implicated. We sought to explore the extent to which the place of birth and the place of treatment influences survival outcomes in Korean and US patients with localized gastric cancer. Methods: Patients with localized gastric adenocarcinoma undergoing potentially curative gastrectomy from 1989 to 2010 were identified from the SEER registry and two single institution databases from the US and Korea. Patients were categorized into three groups: Koreans born/treated in Korea (KK), Koreans born in Korea/treated in the US (KUS), and White Americans born/treated in the US (W), and disease-specific survival rates compared. Results: We identified 16,622 patients: 3,984 (24.0%) KK, 1,046 (6.3%) KUS, and 11,592 (69.7%) W patients. KK patients had longer unadjusted median (not reached) and 5-year disease-specific survival (81.6%) rates than KUS (87 months, 55.9%) and W (35 months, 39.2%; p < 0.001 for all comparisons) patients. This finding persisted on subset analyses of patients with stage IA tumors, without cardia/GEJ tumors, with > 15 examined lymph nodes, and treated at a US center of excellence. On multivariable analysis, KUS (HR 2.80, p < 0.001) and W (HR 5.79, p < 0.001) patients had an increased risk of mortality compared to KK patients. Conclusions: Both the place of birth and the place of treatment significantly contribute to the improved prognosis of patients with gastric cancer in Korea relative to those in the US, implicating both nature and nurture in this phenomenon.