[Clinical characteristics and prognostic factors of epidermal growth factor receptor-mutated non-small cell lung cancer transformed into small-cell lung cancer after treatment]

Objective: To analyze the clinical characteristics and prognostic factors of non-small cell lung cancer (NSCLC) patients with sensitive epidermal growth factor receptor (EGFR) mutations who developed small cell lung cancer (SCLC) transformation after treatment with EGFR tyrosine kinase inhibitors (TKI). Methods: We conducted a retrospective collection of clinical data for 21 patients with advanced EGFR mutant NSCLC who developed SCLC transformation after EGFR-TKI treatment at Beijing Chest Hospital, Capital Medical University from January 2015 to December 2021. The clinical characteristics were summarized and the prognosis analysis was conducted. Patients were followed up until February 2024. The efficacy was evaluated using Solid Tumor Response Evaluation Criteria, and survival curves were plotted using the Kaplan-Meier method, and the log-rank test was used to compare the differences in survival time (OS) between limited stage and extensive stage in transformed SCLC patients. Cox proportional hazards model was used to analyze the influencing factors of survival after SCLC transformation. Results: Among the 21 patients, there were 5 males and 16 females, with an age range of 33-74 years old [(58.9±2.6) years old]. All 21 patients were adenocarcinoma with sensitive EGFR mutations. There were 18 cases (85.7%) with EGFR gene 19del mutation, including 1 case of 19del+anaplastic lymphoma kinase (ALK) mutation, and 3 cases of L858R mutation. Among the transformed SCLC, there were 11 cases of pure SCLC and 10 cases of mixed SCLC (coexisting of adenocarcinoma and small cell carcinoma components). The median time from diagnosis of NSCLC to SCLC transformation was 12.0 months (95%CI: 7.6-16.3 months). Among the 21 cases of SCLC transformation, there were 13 cases with the extensive stage and 8 cases with the limited stage. Among them, 16 patients received systemic chemotherapy based on etoposide, of which 13 cases could be evaluated for efficacy, 11 cases could be calculated for PFS. Five cases had partial remission, 5 cases were stable, 3 cases had disease progression, and 3 cases cloud not be evaluated. The median progression free survival time (PFS) was 4.8 months (95%CI: 2.8-6.8 months). The median survival time (OS) after SCLC transformation in 21 patients was 10.6 months (95%CI: 7.0-14.2 months), with a median OS of 8.8 months (95%CI: 6.3-11.4 months) for patients with the extensive stage and 27.5 months (95%CI: 9.6-34.4 months) for patients with the limited stage, with statistically significant differences (P=0.002). Cox proportional hazards model analysis showed that the limited stage after SCLC transformation was a protective factor for OS (HR=0.32, 95%CI: 0.12-0.73, P=0.010). The median OS of 21 patients from the diagnosis of lung cancer was 24.9 months (95%CI: 13.0-36.7 months). Conclusions: NSCLC patients with SCLC transformation are all adenocarcinomas, and the proportion of EGFR19del mutations is relatively high. After SCLC transformation, the standard chemotherapy regimen for SCLC is generally used for treatment. The OS after SCLC transformation is related to the stage, and the prognosis is better in the limited stage.