Abstract
562
Purpose: Metabolic tumor volume (MTV) and other quantitative parameters derived from 18F- fludeoxyglucose (FDG) PET/CT have been shown to be prognostic for survival in a variety of malignant tumors treated with chemotherapy. However, little is known about the prognostic value of these parameters in patients with head and neck squamous cell carcinoma (HNSCC), in particular when treated with novel immune checkpoint inhibitors. Therefore, we investigated the prognostic value of pretreatment 18F-FDG PET/CT in patients with advanced HNSCC before treatment with PD1 blockade. . Materials and Methods: Forty patients (median age 61 yrs; range 18 ̶ 87 yrs) with HNSCC treated with PD1 blockade were included (Nivolumab, n=21; Pembrolizumab, n=19). All patients underwent baseline 18F-FDG PET/CT within 2 months before initiation of therapy (median 3.8 wks). All patients received infusions of 3 mg/kg nivolumab every two weeks or 3 mg/kg pembrolizumab every three weeks as one cycle, repeated until discontinuation. Tumor 18F-FDG uptake was quantified by standardized uptake values normalized to lean body mass and further analyzed as follows: (1) highest SULpeak of all lesions in a patient (SUL1), sum of SULpeak of up to 5 lesions (no more than 2 per organ, SUL5), metabolic tumor volume (MTV), and total lesion glycolysis (TLG). MTV of each lesion was defined as the volume encompassed by a 42% isocontour around the voxel with the highest PET uptake. TLG was obtained by multiplying the MTV with the mean SUL in the volume. Total MTV and TLG were calculated by summing MTVs and TLGs of all lesions, respectively. Cox regression and Kaplan-Meier analyses for overall survival (OS) were used to assess the prognostic value of the FDG PET derived parameters and clinical prognostic factors. After multivariate analysis, remaining PET parameters and clinical factors were combined to further stratify patient groups. . Result: Median OS was 10.5 mos (95%CI: 2.13-18.83 mos) and 1 year survival rate was 49%. Median values for SUL1, SUL5, MTV, and TLG were 8.87 g/mL, 16.69 g/mL, 65.68 cm3, and 274.53 g/mL[asterisk]cm3, respectively. TLG, MTV and SUL5, but not SUL1 were significantly associated with OS (Figure 1). After multivariate analysis, patients with MTV above the median and early discontinuation of PD1 blockade ( 4 cycles) showed the worst outcome (Figure 2).
Conclusions: In patients with HNSCC undergoing therapy with immune checkpoint inhibitors, baseline tumor burden on FDG PET as assessed by MTV, TLG or SUL5 is significantly associated with OS. Several recent software packages now enable calculation of MTV in a semiautomatic fashion; therefore, baseline MTV in routine FDG PET/CT scans may be a clinically relevant prognostic parameter in patients undergoing immunotherapy.