Prognostic significance of liver-to-muscle FDG uptake ratio and ınflammatory biomarkers in small cell lung cancer.

Background: Small cell lung cancer (SCLC) is an aggressive malignancy frequently complicated by systemic inflammation, cachexia, and metabolic dysfunction. While 18F-FDG PET/CT is routinely used for disease staging, its potential to reflect host metabolic status through tissue-specific uptake metrics remains underexplored. We investigated the prognostic significance of the liver-to-rectus femoris mean standardized uptake value ratio (LRF) alongside systemic inflammatory markers in patients with SCLC.

Methods: This retrospective study included 155 newly diagnosed SCLC patients who underwent baseline 18F-FDG PET/CT prior to systemic therapy. Quantitative PET/CT metrics-particularly LRF SUVmean-were analyzed in relation to clinical characteristics, inflammatory indices (CRP-to-albumin ratio [CAR], neutrophil-to-lymphocyte ratio [NLR]), and survival outcomes. Kaplan-Meier and multivariate Cox regression analyses were used to assess progression-free survival (PFS) and overall survival (OS).

Results: An elevated LRF ratio (≥ 3.18) was independently associated with shorter PFS (7.52 vs. 10.22 months; p = 0.047) and OS (7.85 vs. 9.40 months; p = 0.021) in extensive-stage SCLC. Similarly, patients with CAR ≥ 0.29 had significantly worse progression-free survival (7.10 vs. 11.50 months; p = 0.001) and overall survival (7.55 vs. 13.74 months; p = 0.008) compared to those with CAR < 0.29. LRF SUVmean positively correlated with CAR and negatively with serum albumin. In contrast, NLR was not significantly associated with survival outcomes.

Conclusion: The LRF SUVmean ratio represents a novel, noninvasive PET/CT-derived biomarker that reflects host metabolic frailty and correlates with systemic inflammation. Integration of metabolic imaging parameters such as LRF with established laboratory markers may improve prognostic stratification in SCLC and guide supportive care strategies.