Early Metabolic Response Evaluation by Fluorine-18 Fluorodeoxyglucose Positron Emission Tomography Allows <i>In vivo</i> Testing of Chemosensitivity in Gastric Cancer: Long-term Results of a Prospective Study

<jats:title>Abstract</jats:title> <jats:p>Purpose: We prospectively evaluated the predictive value of positron emission tomography using fluorine-18 fluorodeoxyglucose (FDG-PET) for in vivo testing of chemosensitivity in locally advanced gastric cancer using an a priori definition of metabolic response (a decrease of &gt;35% of the standard uptake value). The goal of the study was the definition of biologically different groups of patients prior to or early during induction therapy, with special emphasis on FDG non–avid tumors.</jats:p> <jats:p>Experimental Design: Based on our data, which was published in 2003, at least 36 patients with metabolic response or FDG non–avid tumors had to be recruited for an analysis of the group of FDG non–avid tumors with sufficient statistical power. Seventy-one patients (32 metabolic nonresponders, 17 metabolic responders, and 22 patients with FDG non–avid tumors) underwent FDG-PET at baseline. In FDG-avid tumors, FDG-PET was repeated 14 days after the initiation of chemotherapy.</jats:p> <jats:p>Results: Metabolic responders (17 of 49) showed a high histopathologic response rate (69%) and a favorable prognosis (median survival not reached), whereas metabolic nonresponders (32 of 49) had a poor prognosis (median survival, 24.1 months) and showed a histopathologic response in 17%. The histopathologic response rate (24%) for FDG-PET non–avid patients showed no significant difference compared with FDG-avid nonresponders (P = 0.72). Survival of FDG non–avid patients was 36.7 months (not significantly different from FDG-avid nonresponders, 24.1 months, P = 0.46).</jats:p> <jats:p>Conclusion: In locally advanced gastric cancer, three different metabolic groups exist. Response and survival was predicted by PET in FDG-avid tumors. Metabolic response assessment was not possible in FDG non–avid tumors; however, due to unfavorable outcome, therapy modification might also be considered in FDG non–avid tumors.</jats:p>