Conditional survival after surgery for limited-stage small-cell lung cancer: a retrospective study

Background This study aimed to evaluate the impact of disease-free survival (DFS) at 24 months (DFS24) and 36 months (DFS36) on subsequent OS in patients with limited-stage small-cell lung cancer (LS-SCLC) after curative surgery. Methods We retrospectively analyzed 200 patients with LS-SCLC who underwent curative surgery. DFS at 12, 24, 36, 48, and 60 months (DFS12, DFS24, DFS36, DFS48, and DFS60, respectively) was assessed. Subsequent OS was defined as the time from a specified landmark time point (for recurrence-free patients) or from the date of recurrence (for patients with recurrence prior to the landmark) to death. Standardized mortality ratios (SMRs) were used to compare mortality risks in the study cohort with those in an age- and sex-matched general population in China. Results The median follow-up time was 72.1 months for surviving patients. Among stage I–IIA patients ( n = 76), 64 were eligible for analysis at the 24-month landmark. Among these patients, 76.6% ( n = 49) achieved DFS24. The corresponding SMR was 2.08 (95% CI 0.89–4.09; P = 0.086), and the subsequent 5-year OS rate was 74.3%. In patients who did not achieve DFS24 (23.4%), the 3-year subsequent OS rate was 25.0%, with an SMR of 37.17 (95% CI 19.18–64.93; P < 0.001). Among stage IIB–IIIB patients ( n = 124), 95 were eligible for analysis at the 36-month follow-up. Among these patients, 38.9% ( n = 37) achieved DFS36. The corresponding SMR was 1.61 (95% CI 0.43–4.12; P = 0.476), and the subsequent 5-year OS rate was 94.6%. In patients who did not achieve DFS36 (61.1%), the 3-year subsequent OS rate was 8.2%, and the SMR was 66.01 (95% CI 49.44–86.35; P < 0.001). Conclusion Patients who achieved DFS24 (stage I–IIA) or DFS36 (stage IIB–IIIB) had favorable prognoses, with no significant difference in subsequent OS compared with the general population. In contrast, patients with early recurrence had significantly worse survival. DFS24 and DFS36 may serve as exploratory stage-specific landmark time points for postoperative risk stratification and individualized follow-up strategies. Trial registration Retrospective observational study, no clinical trial registration required.