Utility of Assessing Early Tumor Shrinkage as an Efficacy Predictor in Patients with Non-Surgically Indicated or Recurrent Esophageal Cancer Treated with Nivolumab plus Ipilimumab

INTRODUCTION: Nivolumab plus ipilimumab combination therapy has been administered as a first-line treatment in Japan since 2022 for patients with unresectable progressive or recurrent esophageal cancer. The efficacy and safety of this immune checkpoint inhibitor (ICI) doublet therapy are now being evaluated, and it is necessary to identify populations that benefit from this treatment at an early phase after initiation. For patients not showing early benefit, changing as soon as possible to other therapeutic strategies could improve their survival outcomes. Therefore, we attempted to identify decision-making factors such as early tumor shrinkage (ETS) based on treatment experience with ICI doublet therapy. METHODS: The study included 19 patients who received nivolumab plus ipilimumab for non-surgically indicated or recurrent esophageal cancer between July 2022 and November 2023. Tumors were assessed approximately every 2 months after treatment initiation. The effects of ETS, depth of response (DpR), and clinicopathologic features, including immune-related adverse events (irAEs), on progression-free and overall survival were evaluated using Kaplan-Meier plots and Cox proportional hazard models. RESULTS: The mean duration of ICI doublet administration was 5.89 months (range, 1-16 months). At first evaluation, patients who exhibited no tumor progression >20% indicated possible response to ICI doublet therapy, and patients whose tumors shrank even minimally exhibited favorable progression-free survival. Higher DpR at any cut-off line exhibited better progression-free survival than those with lower DpR. Fifteen patients experienced irAEs, with 13 of these patients experiencing irAEs within 3 months of treatment initiation. irAEs were associated with the efficacy of ICI doublet therapy, but efficacy could not be predicted based on early irAE experience. CONCLUSION: ETS-high, DpR-high, and irAEs might be associated with favorable responses to nivolumab plus ipilimumab. As a predictor of efficacy at an early phase, ETS >0% could be a deciding factor for continuing ICI doublet therapy.