A validation study of a novel biomarker-based scoring system (EAST score) for limited-stage small-cell lung cancer: A secondary analysis of JCOG0202 and JCOG1011.

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8081 Background: Concurrent chemoradiotherapy (CCRT) followed by prophylactic cranial irradiation (PCI) is potentially curative for limited-stage small-cell lung cancer (LS-SCLC), yet reliable markers for identifying long-term survivors remain undefined. The Enhanced Assessment for SCLC Treatment (EAST) score was originally derived from a retrospective, single-center training cohort for prognostic stratification of LS-SCLC patients receiving CCRT. This score integrates N3 status, serum lactate dehydrogenase (LDH), pro-gastrin-releasing peptide (ProGRP), and cytokeratin 19 fragment (CYFRA 21-1) levels measured at diagnosis. This study (JCOG2401A) validated its prognostic utility using data from two randomized controlled trials (RCTs) of LS-SCLC. Methods: The validation cohort comprised patients enrolled in JCOG0202 and JCOG1011: randomized phase 3 and 2 studies, respectively, that compared multiple consolidation chemotherapy regimens following CCRT. External validation of the dichotomized EAST score (low: score 0–1, high: 2–5) was performed by assessing discrimination and calibration for progression-free survival (PFS) and overall survival (OS). Exploratory subgroup analyses were conducted in an integrated cohort of the training cohort (N = 224; median follow-up, 64.5 months) and the validation cohort. Hazard ratios (HRs) for PCI were estimated using propensity score-weighted Cox models. Results: Out of 309 patients in these trials, 205 with complete data for EAST score components were included in the validation cohort. Median age was 62 years. Low- vs. high-risk groups showed stage (I-II/III) distributions of 28/72% vs. 11/89%, and tumor response (CR-PR/SD) distributions of 89/3% vs. 91/2%, respectively. The low-risk group (N = 114) showed better outcomes than the high-risk group (N = 91) for both PFS and OS (Table). Integrated cohort analysis revealed a numerical survival benefit from PCI in low-risk patients (N = 214), whereas the benefit was highly limited in the high-risk group (N = 202) (Table). Conclusions: The prognostic value of the EAST score was validated even in external RCT datasets. High-risk patients, characterized by early recurrence and inferior OS, derive minimal benefit from PCI. These findings provide a rationale for a planned risk-adapted RCT utilizing the EAST score. Median PFS, months PFS, HR (95% CI) Median OS, months OS, HR (95% CI) Low- vs. high-risk Training cohort (N=107/117) 20.6/9.4 0.48 (0.34-0.67) 53.0/34.2 0.67 (0.46-0.98) Validation cohort (N=114/91) 25.0/10.7 0.55 (0.40-0.77) 63.2/29.6 0.51 (0.36-0.73) PCI vs. no-PCI All (N=287/129) 14.5/12.9 0.91 (0.65-1.28) 50.0/35.5 0.78 (0.56-1.10) Low risk (N=152/62) 31.3/14.6 0.86 (0.49-1.48) 67.9/40.1 0.75 (0.43-1.31) High risk (N=135/67) 10.2/10.6 0.99 (0.71-1.39) 34.2/30.9 0.86 (0.59-1.28)

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