Distinct Prognostic Roles of 18F-FDG PET Metabolic Response Assessed After Induction Chemotherapy or Chemoradiotherapy in Localized Esophageal Squamous Cell Carcinoma

The prognostic significance of metabolic response by posttreatment 18F-FDG PET in esophageal squamous cell carcinoma (ESCC) treated with chemoradiotherapy remains unclear, particularly regarding metabolic response after induction chemotherapy versus after chemoradiotherapy. This study aimed to evaluate and compare their prognostic impact. Methods: This retrospective study analyzed 604 patients with localized ESCC who received induction chemotherapy followed by chemoradiotherapy, with or without surgery, at Asan Medical Center between 2006 and 2018. Metabolic responses after induction chemotherapy (before chemoradiotherapy) and after chemoradiotherapy were evaluated using European Organisation for Research and Treatment of Cancer-based criteria adapted for prognostic assessment. Results: In patients treated with definitive chemoradiotherapy (bimodality therapy), metabolic response after both induction chemotherapy and chemoradiotherapy was significantly associated with progression-free survival (PFS) and overall survival (OS). Complete metabolic response after induction chemotherapy correlated with the longest survival (PFS, 58.9 mo; OS, 90.8 mo), whereas progressive metabolic disease predicted poor prognosis (PFS, 3.7 mo; OS, 7.0 mo; P < 0.001). A similar pattern was observed for postchemoradiotherapy metabolic response. In patients who underwent surgery (trimodality therapy), metabolic response after induction chemotherapy did not significantly impact survival. However, in patients for whom surgery was initially planned, it remained prognostic, suggesting its prognostic relevance in the preoperative setting. Postchemoradiotherapy metabolic response was a strong independent prognostic factor in both bimodality therapy and trimodal therapy. Patients with diffuse esophagitis after chemoradiotherapy had intermediate survival outcomes, among complete metabolic response and partial metabolic response groups, indicating a distinct prognostic pattern. Conclusion: Postchemoradiotherapy metabolic response is a strong prognostic marker in localized ESCC, supporting its use for risk stratification. Early metabolic response after induction chemotherapy may also inform treatment decisions, particularly in surgery-intended patients.