Efficacy of ¹⁸F-Fluoro-2-Deoxyglucose Positron Emission Tomography as a Predictor of Treatment Response to Neoadjuvant S-1 + Oxaliplatin Chemotherapy for Gastric Cancer

Background: Neoadjuvant chemotherapy is widely recognized as the established treatment for advanced gastric cancer. However, predicting its efficacy before surgery remains challenging. Aim: The present study aimed to evaluate the effectiveness of 18F-fluoro-2-deoxyglucose positron emission tomography (FDG-PET) as a predictor of treatment response to the S-1+Oxaliplatin regimen (SOX). Methods and Results: Thirty patients who underwent gastrectomy following neoadjuvant SOX between January 2021 and July 2023 were included. Patients underwent FDG-PET pre- and postsurgery. The maximum standardized uptake value (SUVmax) from FDG-PET was examined in relation to histological tumor response and prognosis. SUVmax decreased significantly after chemotherapy in all patients (p < 0.001), especially in those with Grade 1a, 2, and 3 tumors (p < 0.05). SUV reduction increased stepwise with the histological response grade. Optimal cut-off values for the percentage decrease in SUVmax (ΔSUVmax) predictive of histologic efficacy were identified as 53% (area under curve 0.855, p = 0.0018) for Grade 1b or higher and 75% (area under curve 0.806, p = 0.0044) for Grade 2 or higher. Patients with ΔSUVmax > 50% had improved recurrence-free survival (p = 0.027). Conclusion: FDG-PET may be useful as a predictor of treatment response in neoadjuvant SOX therapy for gastric cancer. The determination of the optimal ΔSUVmax value may enhance the precision of histological tumor response prediction.