Clinical characteristics and survival of small cell lung cancer with limited or extensive synchronous metastatic spread − A German population-based cancer-registry based cohort study

Introduction While the concept of oligometastatic disease (OMD) is established in non-small cell lung cancer (NSCLC), its relevance in small cell lung cancer (SCLC) remains unclear. We investigated whether subclassifying metastatic SCLC by the TNM-8 M classification and the number of organ systems involved provides prognostic value and informs the applicability of the OMD concept to SCLC. Materials and methods Patients with stage IV SCLC diagnosed between 2016 and 2020 were identified from three German population-based cancer registries. Metastatic burden was categorized as intra-thoracic limited metastatic spread (IT-LMS, M1a), extra-thoracic limited metastatic spread (ET-LMS, M1b), limited multi-organ involvement (LMOI, M1c with ≤3 organs), or extensive multi-organ involvement (EMOI, M1c with >3 organs). Overall survival (OS) and progression-free survival (PFS) were estimated using the Kaplan-Meier method. Multivariable Cox models evaluated the prognostic relevance of metastatic extent and specific metastasis sites. Results Among 2,567 patients, 9.5% had IT-LMS, 18.5% ET-LMS, 60.9% LMOI, and 11.1% EMOI. Median OS was 11 months in IT-LMS and ET-LMS, 8 months in LMOI, and 7 months in EMOI. PFS showed a similar gradient (6.1, 6.0, 4.1, and 4.1 months). Compared with IT-LMS, mortality risk was higher in LMOI (HR 1.57, 95% CI 1.34–1.84) and EMOI (HR 1.87, 1.54–2.28); EMOI also exceeding LMOI (HR 1.19, 1.04–1.37). Liver and brain metastases reduced OS in LMOI, while pleural carcinomatosis reduced PFS in IT-LMS. Conclusion Our results indicate that limited metastatic spread can be identified in SCLC and has prognostic value. This supports the consideration of an SCLC-specific definition of OMD.