Characteristics of patients with non-small cell lung cancer and either limited or extensive synchronous metastatic spread in Germany—a population-based cancer registry cohort study

Background: Oligometastatic disease, i.e., disease with limited metastatic spread (LMS), is increasingly recognised as a distinct clinical entity as it differs from disease with extensive metastatic spread (polymetastatic disease) in terms of treatment and prognosis. This retrospective observational study aimed to characterise a population-based cohort of non-small-cell lung cancer (NSCLC) patients with synchronous metastatic disease, stratified by the extent of metastatic spread. Methods: NSCLC patients [≥18 years, diagnosed 2016–2020, ICD-10 C34, Union for International Cancer Control (UICC) stage IV at primary diagnosis] were identified from three German population-based cancer registries covering approximately 27% of the national population. The extent of metastatic disease was classified according to the 8^th edition of the tumour-node-metastasis (TNM) system and further subclassified by the number of organ systems involved. We differentiated between patients with TNM-M stage M1a (intra-thoracic LMS), M1b [one single extra-thoracic metastasis or extra-thoracic LMS (ET-LMS)], M1c and ≤3 [limited multi-organ involvement (LMOI)] and >3 organ systems involved or with generalised metastatic disease [extensive multi-organ involvement (EMOI)]. The intent of the statistical analysis was mainly descriptive. Results: The cohort included 8,033 NSCLC patients with distant metastasis at diagnosis of the primary tumour (1,767 with intra-thoracic LMS, 1,314 with ET-LMS, 4,196 with LMOI and 756 with EMOI). Patients with EMOI were younger (median: 64 vs. 66–70 years), more often female (45.0% vs. 40.6–41.4%), had a higher proportion of adenocarcinomas (83.7% vs. 72.2–78.7%) and showed more frequent N3 lymph node involvement (37.8% vs. 22.9–30.4%) than patients with LMS (subgroups: intra-thoracic LMS, ET-LMS or LMOI). Patients in the ET-LMS subgroup most often presented with one brain, osseous or adrenal metastasis (in descending order), patients in the LMOI subgroup most often with osseous, brain and/or pulmonal metastases, while patients in the EMOI subgroup presented most often with osseous, hepatic and/or pulmonal metastases. Patients were followed-up for a median time of 7 months (interquartile range, 3–16 months), during which every fourth patient with initially LMS experienced a new metastasis with mainly limited spread, usually in another organ than at primary diagnosis. Brain and osseous metastases were most frequently observed during follow-up. Conclusions: We were able to identify patients with LMS in a population-based real-world dataset. This large data source forms the basis of a study series, in which subsequent analyses will assess survival prospects and optimal treatment strategies for this therapeutically relevant patient group.