Prediction of tumor response by FDG-PET: Comparison of the accuracy of single and sequential studies in patients with adenocarcinomas of the esophagogastric junction

Purpose: Positron-emission-tomography with the glucose analog fluorodeoxyglucose (FDG-PET) has shown encouraging results for prediction of tumor response to chemotherapy. However, there is no consensus as to what time after initiation of therapy FDG-PET should be performed. To address this question we studied the time course of changes in tumor FDG-uptake in patients with locally advanced adenocarcinomas of the esophagogastric junction (AEG) treated with preoperative chemotherapy. Methods: Twenty-four patients with AEG were included and underwent FDG-PET prior to therapy (PET1), 2 weeks after initiation of therapy (PET2), and preoperatively (PET3). Tumor metabolic activity was assessed by standardized uptake values (SUV) and correlated with histopathologic response and patient survival. Results: Baseline tumor SUV was 8.3±3.5 and decreased to 5.0±1.8 at PET2 (p<0.0001). At PET3 there was further decrease to 3.5±1.9 (p<0.0001). The relative decrease of tumor FDG-uptake from PET1 to PET2 and from PET1 to PET3 were both significantly correlated with histopathologic response. Reduction of tumor SUV from PET1 to PET2 was significantly correlated with survival (p=0.03) and there was a similar trend for changes from PET1 to PET3 (p=0.09). In contrast, absolute SUVs did not demonstrate a significant correlation with histopathological response or patient survival at any of the studied time points. Conclusion: In patients with AEG, relative changes in tumor FDG uptake are better predictors for treatment outcome than absolute SUVs. Metabolic changes within the first 2 weeks of therapy are at least as efficient for prediction of histopathologic response and patient survival as later changes.