Genomic Profiling, Risk Stratification, and Post-Transformation Treatment Outcomes in Patients with Transformed Small-Cell Lung Cancer: A Multicenter Analysis.

BACKGROUND: Transformed small-cell lung cancer (T-SCLC) is an increasingly recognized resistance mechanism in EGFR-mutant lung adenocarcinoma. This study aimed to identify early predictors of histologic transformation and evaluate post-transformation treatment outcomes. METHODS: We retrospectively collected 163 T-SCLC patients from five Chinese centers. Next-generation sequencing was performed on 60 EGFR-mutant patients, including 47 paired primary-transformed samples. Integrated genomic and clinical analyses were conducted to delineate molecular features and survival outcomes. RESULTS: Among 150 EGFR-mutant patients, the median time to SCLC transformation was 25.8 months and median post-transformation overall survival (OS) was 14.2 months. Clinical and survival data for the 13 EGFR wild-type patients are reported descriptively given the limited sample size. Among 108 treatment-evaluable patients, first-line EGFR-TKI plus chemotherapy, chemotherapy alone, and immune checkpoint inhibitors (ICIs) plus chemotherapy yielded median progression-free survival (PFS) of 6.2, 5.30, and 4.07 months (P = 0.041) and median OS of 21.2, 27.6, and 13.6 months (P = 0.193). In later-line therapy, taxane-based regimens achieved a median PFS of 6.93 months, outperforming camptothecin-based (1.13 months) and other regimens (1.90 months; P = 0.049). High evolutionary diversity was associated with shorter post-transformation OS (6.77 vs. 11.10 months), with restricted cubic spline analysis showing a nonsignificant trend toward a nonlinear association (P = 0.055).Age, RB1/NTRK1 mutation, and secondary T790M mutation were identified as independent risk factors and integrated into a predictive model with high accuracy. CONCLUSIONS: This study establishes a clinically applicable model for early prediction and risk stratification of SCLC transformation. Taxane-based regimens emerge as a promising later-line therapeutic option for T-SCLC.