Disparities in gastric cancer treatment and related adverse events in older adults

Background: Disparities in treatment-related adverse events (AEs) may contribute to racial differences in cancer outcomes. In this study, we performed a comprehensive analysis of treatment patterns and related AEs between non-Hispanic White (NHW) and non-Hispanic Black (NHB) gastric cancer (GC) patients. Methods: We queried SEER-Medicare (2000-2017) for NHW and NHB patients aged ≥66 years with histologically confirmed GC. Inpatient and outpatient claims within 1 year of diagnosis were collected for chemotherapy, surgery, and radiation treatments. Chemotherapy treatments were classified as ‘NCCN' if consistent with first/second-line regimens per 2025 NCCN GC guidelines, and ‘non-NCCN' otherwise. Chemotherapy-related AEs were identified using hospitalization claims for hematologic, gastrointestinal, infectious, and metabolic toxicities within 21 days of treatment consistent with prior SEER-Medicare studies. Cohort differences were tested with χ² or t-tests. To control for repeated observations (e.g., treatment cycles) per patient, we used multivariable Generalized Estimating Equations to measure associations between race and AEs. Results: The cohort included 18,089 patients (15,824 NHW; 2,265 NHB). SEER stage distribution was consistent across both NHW and NHB cohorts (33% vs. 34% metastatic disease, P =0.32). NHW patients were more often male (64% vs. 55%, P <0.01) and had more cardia primaries (59.9% vs. 37.0%, P <0.01), while NHBs had higher comorbidities (mean NCI Index 0.64 vs. 0.50, P <0.01). NHBs were less likely to receive chemotherapy (aOR 0.80, 95% CI 0.71-0.89) or radiation (aOR 0.76, 95% CI 0.66-0.86), and had longer mean time to treatment initiation (chemotherapy: 82 vs. 73 days; radiation: 100 vs. 85 days; both P <0.01) than NHWs. Among 5,748 chemotherapy recipients (5,147 NHW; 601 NHB), mean treatment cycles did not differ between NHWs and NHBs (5.0 vs. 5.2, P =0.19). However, NHBs had higher AE risk (aOR 1.15, 95% CI 1.02-1.30) per treatment than NHWs. Metastatic disease (aOR 1.49, 95% CI 1.39-1.59) and non-NCCN regimens (aOR 1.31, 95% CI 1.22-1.40) were also associated with elevated AE risk. Further sub-group analyses showed higher AE risk for NHBs relative to NHWs in the non-NCCN cohort (aOR 1.35, 95% CI 1.10-1.65) but not in the NCCN cohort (aOR 1.11, 95% CI 0.95-1.28). Conclusions: NHB patients with GC were less likely to receive chemotherapy or radiotherapy and experienced longer treatment delays than NHW patients. NHB patients also had greater risk of chemotherapy-related AEs, particularly when using non-NCCN regimens. These findings highlight persistent inequities in GC care and support further investigation into structural and biological drivers of AE disparities.