Significance of ¹⁸ F-Fluorodeoxyglucose (FDG) Uptake in Response to Chemoradiotherapy for Pancreatic Cancer

Background: A metabolic shift to glycolysis is reportedly involved in radioresistance. We examined whether pretreatment ¹⁸ F-fluorodeoxyglucose positron emission tomography (FDG-PET), which can detect enhanced glucose uptake, was able to predict the therapeutic response to chemoradiotherapy (CRT) in patients with pancreatic cancer (PC). Methods: Of 125 PC patients (75 unresectable and 50 borderline resectable), 37 and 26 underwent induction chemotherapy before CRT and surgical resection after CRT, respectively. FDG-PET was performed at three different institutions. Results: Of the 88 patients who underwent upfront CRT, 31 (35%), 34 (39%), and 23 (26%) showed a partial response (PR), stable disease, and progressive disease, respectively. The tumor PR rate was an independent factor associated with longer overall survival (OS) on multivariate analysis. We evaluated the optimal cut-off of maximum standardized uptake values (SUV _max ) at initial diagnosis to detect the tumor PR rate at the three institutions separately. The SUV _max was independently associated with tumor response rate on multivariate analysis. In the low SUV _max group, induction chemotherapy had no significant impact on OS. In contrast, induction chemotherapy was significantly associated with longer OS in the high SUV _max group. Conclusions: FDG-PET SUV _max was significantly associated with the therapeutic response to CRT in PC patients. Moreover, induction chemotherapy may improve the prognosis of patients with a high SUV _max tumor.