(1) Background: Nivolumab plus chemotherapy is established as a first-line treatment for advanced gastric cancer (AGC). While mFOLFOX6 is commonly used for AGC with severe peritoneal metastasis, the efficacy of nivolumab combined with it remains uncertain. We evaluated the outcomes of nivolumab plus mFOLFOX6 for AGC with severe peritoneal metastasis in clinical practice. (2) Methods: This multicenter retrospective study was conducted between December 2021 and June 2023. We investigated AGC patients with massive ascites or inadequate oral intake due to severe peritoneal metastasis and who received nivolumab plus mFOLFOX6. (3) Results: Among 106 patients treated with nivolumab plus chemotherapy, 21 (19.8%) had severe peritoneal metastasis, with 14 receiving nivolumab plus mFOLFOX6. The median progression-free survival was 7.4 months (95%CI 1.9-10.1), and the median overall survival was 10.7 months (95%CI 5.3-NA), with four patients (28.5%) surviving more than 12 months. Improved ascites and oral intake were observed in 6/14 patients (42.8%) and 10/11 patients (90.9%), respectively. The major grade 3 or more adverse events included leukopenia (28.5%) and neutropenia (21.4%), with no severe immune-related adverse events reported. (4) Conclusions: The safety and moderate efficacy of nivolumab plus mFOLFOX6 were suggested even in AGC patients with severe peritoneal metastasis.

Background/Objectives: Recently, pembrolizumab plus 5-fluorouracil and cisplatin (FP), nivolumab plus FP, and nivolumab plus ipilimumab have become the first-line treatments for patients with advanced esophageal cancer. However, the treatment efficacy in primary tumors has not been reported. We assessed the outcomes of these treatments in advanced esophageal cancer, specifically focusing on esophageal dysphagia improvements and the primary tumor response. Methods: This retrospective study was conducted between October 2021 and November 2023. We investigated 23 patients with esophageal cancer and dysphagia who received an immune checkpoint inhibitor (ICI) plus FP or nivolumab plus ipilimumab. Results: The median progression-free survival (PFS) was 10.6 months (95% confidence interval [CI]: 9.0–12.5), and the median overall survival was not reached (95%CI: 13.0–NA). Improvement in dysphagia was observed in 19/23 (82.6%) patients, with a median time to improvement of 26 days (range: 15–77 days) and a median dysphagia PFS of 12.6 months (range: 8.1–NA months). Ten patients experienced immune-related adverse events (irAEs): seven had interstitial pneumonia, and three had thyroid dysfunction, pituitary dysfunction, and rash, respectively. Conclusions: Although there was a high frequency of irAEs, ICI for esophageal cancer achieved high response rates and prolonged survival. The observed improvement in dysphagia suggests the potential efficacy of the treatment against primary tumors.