149P Total metabolic tumor volume: A new potential prognostic factor in SCLC

Abstract

Small-cell lung cancer (SCLC) is a highly aggressive lung cancer, often diagnosed at extensive stage (ES-SCLC). The addition of programmed-death ligand 1 (PD-L1) inhibitors to first-line chemotherapy benefits a limited subset of ES-SCLC patients, suggesting the need for better prognostic stratification. [18F]FDG-PET/CT is commonly used for the staging of SCLC and derived metabolic parameters could predict patient outcomes by measuring the extension of metabolically active tumor (metabolic tumor volume [MTV]) or its metabolic heterogeneity (total lesion glycolysis [TLG]). We sought to analyze if these metabolic parameters are prognostic factors in ES-SCLC. We retrospectively collected patients with pathologically confirmed diagnosis of SCLC, who had undergone a [18F]FDG PET/CT scan ≤ 30 days from first-line treatment for ES-SCLC start. Patients with LS-SCLC at diagnosis were included if relapse occurred ≥ 90 days after the end of treatment with radical intent. We calculated total MTV (tMTV) and total TLG (tTLG), by summing each single lesion’s MTV and TLG respectively. The primary endpoint was overall survival (OS) from [18F]FDG PET/CT scan and progression-free survival (PFS) from treatment start. A total of 86 ES-SCLC patients (median age 68, 55% male) were included. Patients with Na+ <135 mEq/L, hypoalbuminemia and elevated LDH levels were associated with greater tMTV, and higher tTLG. At a median follow-up of 20.9 months, the median OS was 11.1 months and median PFS 6.2 months. Hypoalbuminemia, high LDH, thoracic radiotherapy, radiological response, number of lesions and tMTV, but not tTLG, were independently associated with OS. Brain metastases, SUVmax and tMTV, but not tTLG, were associated with the risk of progression. With a tMTV 245.7 cm3 cut-off calculated by ROC curve, patients with low tMTV had longer OS (11.9 vs 4.8 months) and PFS (7.1 vs 4.7 months) than those with high tMTV. High tMTV was independently associated with the risk of death (HR: 7.15), but not with the risk of progression. tMTV, but not tTLG, is an independent prognostic factor in patients with ES-SCLC, suggesting a potential role as stratification factor in patients candidate to first-line treatment.