The prognostic role and association of 18F-FDG PET CT and HER2 expression in gastric cancer

Human epidermal receptor 2 (HER2) status predicts therapy response with antibody targeted to HER2 in gastric cancer. The objective of this study was to examine the clinical value and relationship of pretreatment fluorine-18 fluorodeoxyglucose positron emission tomography computed tomography (18F-FDG PET/CT) and HER2 status in gastric cancer. Retrospective review of 141 gastric cancer patients at our institution between January 2005 and December 2014 who had baseline 18F-FDG-PET/CT before chemotherapy. SUVmax of the primary lesion was recorded, and whole body metastatic burden was calculated using PET metabolic parameters (SUVmax, SUVmean, MTV, TLG) on all metabolically active metastatic lesions (SUV threshold ≥2.5 or 40% isocontour for ≤2.5). Gastric cancers of HER2 positivity had higher FDG uptake compared to HER2 negative of diffuse type pathology (SUVmax of the primary lesion, 9.9 vs. 5.9, p < 0.001). HER2 positive gastric cancer also had larger metabolically active metastatic burden compared to HER2 negative gastric cancers (SUVmax 12 vs. 7.4, p < 0.001; SUVmean 4.9 vs. 3.3, p < 0.001; MTV 146.5 vs. 93.6, p = 0.031, and TLG 764.8 vs. 331, p = 0.002). The high TLG group (>1200) showed significantly shorter PFS and OS compared to the low TLG group (PFS, 5.3 vs. 6.9 months, p = 0.026; OS, 8.2 vs.14.6, months, P < 0.001). In multivariate analysis, TLG and MTV were independent prognostic factors for PFS (TLG, HR = 2.01, 95% CI, 1.27-3.20, p = 0.003; MTV, HR = 2.13, 95% CI, 1.49-3.61, p < 0.001) and OS (TLG, HR = 2.41, 95% CI, 1.57-3.71, p < 0.001; MTV, HR = 2.16, 95% CI, 1.42-3.28, p < 0.001). HER2 positive gastric cancer had higher FDG uptake in the primary lesion compared to HER2 negative cancers, and had higher metabolically active metastatic burden. In addition, whole body TLG and MTV may be more useful than SUVmean and SUVmax for predicting survival in gastric cancer.