Changing cause-of-death composition among patients undergoing gastrectomy for stage I–III gastric adenocarcinoma: a SEER landmark competing-risk analysis of mortality from diagnosis

Among patients selected by receipt of gastrectomy, the composition of subsequent mortality may change with accrued survival. We analysed 29,435 patients with stage I–III gastric adenocarcinoma in the SEER 17 Registries (2004–2021). Because SEER does not record surgery dates, time was measured from diagnosis; estimates are not postoperative survival. Gastric-cancer and other-cause deaths were treated as competing events among patients observed beyond 0-, 1-, 3-, and 5-year landmarks. The other-cause share of deaths during the subsequent five years increased from 21.5% (95% CI 20.8–22.1; n = 29,435) to 25.4% (24.5–26.2; n = 23,443), 44.5% (43.0–45.9; n = 15,289), and 61.8% (60.0–63.6; n = 10,894), although gastric cancer remained the leading cumulative cause of death from diagnosis. Among five-year survivors, five-year cumulative incidences were 11.4% for gastric-cancer death and 18.4% for other-cause death, indicating that the rising share chiefly reflected declining cancer-specific risk. The calendar-eligible five-year-landmark estimate was 62.0% (59.9–64.0; n = 7,301). Reclassifying all 1,322 other or ill-defined deaths as gastric-cancer deaths reduced it to 49.1% (47.1–51.0), while the increase across landmarks persisted. Competing mortality therefore contributes increasingly among longer-term survivors, but any share above one-half is sensitive to cause-of-death classification.