Prognostic value and clinical correlations of 18-fluorodeoxyglucose metabolism quantifiers in gastric cancer

AIM: To investigate the correlations of pre-treatment positron emission tomography-computer tomography (PET-CT) metabolic quantifiers with clinical data of unstratified gastric cancer (GC) patients. METHODS: Forty PET-CT scans utilising 18-fluorodeoxyglucose in patients who received no prior treatment were analysed. Analysis involved measurements of maximum and mean standardised uptake volumes (SUV), coefficient of variation (COV), metabolic tumour volumes and total lesion glycolysis of different thresholds above which the tumor volumes were identified. The threshold values were: SUV absolute value of 2.5, 30% of SUVmax, 40% of SUVmax, and liver uptake-based (marked (2.5), (30), (40) and (liv), respectively). Clinical variables such as age, sex, clinical stage, performance index, weight loss, tumor histological type and grade, and CEA and CA19.9 levels were included in survival analysis. Patients received various treatment modalities appropriate to their disease stage and the outcome was defined by time to metastasis (TTM) and overall survival (OS). Clinical and metabolic parameters were evaluated by analysis of variance, receiver operating characteristics, univariate Kaplan-Meier, and multivariate Cox models. P < 0.05 was considered statistically significant. RESULTS: Significant differences were observed between initially disseminated and non-disseminated patients in mean SUV (6.05 vs 4.13, P = 0.008), TLG(2.5) (802 cm(3) vs 226 cm(3); P = 0.031), and TLG(30) (436 cm(3) vs 247 cm(3), P = 0.018). Higher COV was associated with poor tumour differentiation (0.47 for G3 vs 0.28 for G1 and G2; P = 0.03). MTV2.5 was positively correlated to patient weight loss (< 5%, 5%-10% and > 10%: 40.4 cm(3) vs 123.6 cm(3) vs 181.8 cm(3), respectively, P = 0.003). In multivariate Cox analysis, TLG(30) was prognostic for OS (HR = 1.001, 95% CI: 1.0009-1.0017; P = 0.047) for the whole group of patients. In the same model yet only including patients without initial disease dissemination TLG(30) (HR = 1.009, 95% CI: 1.003-1.014; P = 0.004) and MTV2.5 (HR = 1.02, 95% CI: 1.002-1.036; P = 0.025) were prognostic for OS; for TTM TLG(30) was the only significant prognostic variable (HR = 1.006, 95% CI: 1.001-1.012; P = 0.02). CONCLUSION: PET-CT in GC may represent a valuable diagnostic and prognostic tool that requires further evaluation in highly standardised environments such as randomised clinical trials.