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.