Local tumour therapy for small cell lung cancer with limited or extensive metastasis: An analysis based on data from three German population-based cancer registries

Abstract

Background: There is evidence that adding local thoracic radiotherapy (TRT) to systemic anticancer treatment (SACT) can improve survival in stage IV small cell lung cancer (SCLC) overall and in the oligometastatic subgroup. There is currently no consensus on the use of concomitant or consolidative TRT during or after SACT. Objectives: We investigated how frequently patients with SCLC with limited or extensive metastasis were treated with guideline-concordant SACT (with or without TRT) and how overall survival (OS) and progression-free survival (PFS) varies according to therapy and extent of metastatic spread. Materials and methods: Data from three German cancer registries were requested, harmonised and pooled. After identifying cases with SCLC, synchronous metastasis and guideline-concordant SACT with and without concomitant or consolidating TRT, a propensity score was calculated using logistic regression. The stabilised inverse probability of treatment weighting (siPTW) method was used for weighting. The Kaplan–Meier method was used to estimate OS and PFS (landmark analysis). Differences between groups with different metastatic spread were tested using a log-rank test for weighted data. Results: In this study, 1198 patients with distant metastasised SCLC received guideline-compliant SACT, 10.6% of whom also received TRT. TRT was associated with a survival benefit (median OS: 14 vs. 10 months; median PFS: 6 vs. 4 months; p < 0.05 each). This was particularly true for oligometastatic patients with one extra-thoracic metastasis (extra-thoracic limited metastatic spread; median OS: 21 vs. 11 months; median PFS: 8 vs. 5 months; p < 0.05 each) and for patients with metastasis limited to a maximum of three organ systems (limited multiorgan involvement; median OS: 11 vs. 9 months; median PFS: 6 vs. 4 months; p < 0.05 each). Conclusion: In the data from three population-based cancer registries, we were able to identify cases with one extra-thoracic metastasis (M1b; extra-thoracic limited metastatic spread) using the TNM classification and, by additionally taking into account information on the location of the distant metastases, also cases with distant metastases limited to a maximum of three organ systems (limited multiorgan involvement) and distinguish them from cases with generalised or polymetastasis (extended multiorgan involvement). TRT was associated with survival benefits, particularly in cases with oligo- or limited metastasis to a few organ systems. Survival benefits and possible toxicity of TRT must be taken into account when deciding on treatment.