Extra-thoracic tumor burden but not thoracic tumor burden on (18)F-FDG PET/CT is an independent prognostic biomarker for extensive-disease small cell lung cancer

Abstract

Purpose: The aim of this study was to evaluate the relationship and difference in prognostic significance between whole-body tumor burden, thoracic tumor burden, and extra-thoracic tumor burden on (18)F-FDG PET/CT for patients with extensive-disease small cell lung cancer (ED-SCLC).

Materials and methods: We performed a retrospective, two-center analysis for patients with ED-SCLC who underwent pretreatment (18)F-FDG PET/CT. Metabolic tumor burden was estimated using whole-body metabolic tumor volume (MTV(WB)), thoracic metabolic tumor volume (MTV(TRX)), extra-thoracic metabolic tumor volume (MTV(EXT)), and the number of extra-thoracic tumor foci. Uni- and multivariate analyses were performed using various clinical factors and the metabolic indices.

Results: A total of 91 patients were eligible for this study. MTV(WB) showed stronger correlation with MTV(EXT) than MTV(TRX) (r(2) = 0.804 vs. 0.132, p < 0.001, both), whereas no correlation was observed between MTV(EXT) and MTV(TRX) (r(2) = 0.007, p = 0.428). Patients with smaller MTV(WB), MTV(EXT), and extra-thoracic tumor foci showed longer survival than patients with larger MTV(WB), MTV(EXT), and extra-thoracic tumor foci, respectively, whereas the survival difference between patients with smaller MTV(TRX) and those with larger MTV(TRX) was not significant. Results of uni- and multivariate analyses showed that ECOG performance status (HR = 2.31, p = 0.015), initial chemotherapy cycles (HR = 0.24, p < 0.001), and the number of extra-thoracic tumor foci (HR = 2.75, p < 0.001) were independent prognostic factors for overall survival, and initial chemotherapy cycles (HR = 0.25, p < 0.001), and MTV(EXT) (HR = 2.04, p = 0.013) were independent prognostic factors for progression-free survival.

Conclusion: These data provide evidence indicating that extra-thoracic tumor burden but not thoracic tumor burden is an independent prognostic biomarker for ED-SCLC, and support further exploration of novel treatment strategies targeting extra-thoracic tumor burden in order to improve the clinical outcomes of patients with ED-SCLC.

Keywords: (18)F-FDG PET/CT; Biomarker; Extensive disease small cell lung cancer; Metabolic tumor volume; Oligometastases; Prognosis.