18F-FDG metabolic tumor volume and total glycolytic activity of oral cavity and oropharyngeal squamous cell cancer: adding value to clinical staging.

UNLABELLED (18)F-FDG metabolic tumor volume (MTV) and total glycolytic activity (TGA) have been proposed as potential prognostic imaging markers for patient outcome in human solid tumors. The purpose of this study was to establish whether MTV and TGA add prognostic information to clinical staging in patients with oral and oropharyngeal squamous cell carcinomas (SCCs). METHODS The Institutional Review Board approved this Health Insurance Portability and Accountability Act-compliant single-institution retrospective study. Forty-five patients with histologically proven oral or oropharyngeal SCC underwent PET/CT for initial cancer staging and were included in the study. MTV was measured using a gradient-based method (PET Edge) and fixed-threshold methods at 38%, 50%, and 60% of maximum standardized uptake value (SUV). The TGA is defined as MTV × mean SUV. Bland-Altman analysis was used to establish the reliability of the methods of segmentation. Outcome endpoints were overall survival (OS) and progression-free survival. Cox proportional hazards univariate and multivariate regression analyses were performed. RESULTS In Cox regression models, MTV and TGA were the only factors significantly associated with survival outcome after adjusting for all other covariates including American Joint Committee on Cancer (AJCC) stage, with hazards ratio of 1.06 (95% confidence interval, 1.01-1.10; P = 0.006) and 1.00 (95% confidence interval, 1.00-1.01; P = 0.02). The model fit was significantly better when MTV was added to AJCC stage in model I (χ(2) value change, 1.16-6.71; P = 0.01) and when TGA was added to AJCC stage in model II (χ(2) value change, 1.16-4.37; P = 0.04). The median cutoff point of 7.7 mL for primary tumor MTV was predictive of time to OS (log rank P = 0.04). The median cutoff point of 55 g for PET Edge primary tumor TGA was predictive of time to OS (log rank P = 0.08), though the result was not statistically significant. CONCLUSION Gradient-based segmentations of primary tumor MTV and TGA are potential (18)F-FDG markers for time to survival in patients with oral and oropharyngeal SCC and may provide prognostic information in addition to AJCC stage. These exploratory imaging markers need validation in larger cohort studies.