2395 - Impact of Prolonged Overall Treatment Time on Prognosis in Patients with Limited-Stage Small-Cell Lung Cancer Treated with Definitive Chemoradiotherapy

Purpose/Objective(s): Definitive chemoradiotherapy (CRT) using twice-daily accelerated hyperfractionation (AHF) (45 Gy in 30 fractions) is the standard treatment for limited-stage small-cell lung cancer (LS-SCLC). The trial that established this regimen mainly included White and Black patients, with other ethnic groups comprising 3% of the population. This regimen is also used in Japan; however, radiotherapy interruptions are frequently observed, suggesting it may be too intensive for patients with smaller body sizes, such as many Asian patients. Although AHF is designed to shorten overall treatment time (OTT), interruptions may prolong it, potentially reducing therapeutic efficacy. The purpose of this study was to retrospectively investigate the association between prolonged OTT and prognosis in patients with LS-SCLC treated with definitive CRT.

Materials/Methods: A total of 93 patients with LS-SCLC treated with definitive CRT at 4 hospitals between January 2010 and December 2024 were enrolled. Patients were categorized into 3 groups based on OTT: short-term (=22 days), intermediate-term (23–29 days), and long-term (=30 days). Survival was analyzed with the Kaplan-Meier method, and intergroup comparisons used the log-rank test. Cox proportional hazards models were applied for univariate and multivariate analyses.

Results: The median follow-up period was 30 (range, 3–141) months. Radiotherapy interruptions were observed in 55 patients (59.1%). The median interruption duration was 3 (range, 1–11.5) days. The most common cause of interruption was Grade 4 neutropenia (n=48). The median OTT was 24 (range, 19–35) days. Compared to the other groups, patients in the long-term group had significantly worse overall survival (OS) (p=0.034), with a trend toward poorer progression-free survival (PFS) (p=0.076). In univariate analysis, performance status (=1), low BMI, high Pro-GRP, and OTT (=30 days) were significant prognostic factors for OS. In multivariate analysis, low BMI (p=0.023) and high Pro-GRP (p=0.026) were identified as independent poor prognostic factors for OS. For PFS, univariate analysis identified low BMI, high Pro-GRP, and OTT (=30 days) as significant prognostic factors, while multivariate analysis confirmed low BMI (p=0.002), high Pro-GRP (p=0.0001), and OTT (=30 days) (p=0.035) as independent poor prognostic factors.

Conclusion: A prolonged OTT of 30 days or longer in patients with LS-SCLC treated with definitive CRT was associated with a poorer prognosis