Phase II Trial of Adjuvant S-1 Following Neoadjuvant Chemotherapy and Surgery in Patients with Locally Advanced Esophageal Squamous Cell Carcinoma: The PIECE Trial.

Background: Neoadjuvant chemotherapy followed by surgery (NAC-S) is the standard therapy for locally advanced esophageal squamous cell carcinoma (ESCC) in Japan.

Objective: The aim of this phase II trial was to assess the efficacy and safety of the addition of adjuvant S-1 after R0 resection in ESCC patients who received NAC-S.

Patients and methods: Key eligibility criteria included clinical stage IB-III (without T4 disease) ESCC, age 20-75 years, and an Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1. Patients received adjuvant therapy with four cycles of S-1 (80 mg/m²/day) administered orally for 4 weeks of 6-week cycles. The primary endpoint was 3 year relapse-free survival (RFS). If the lower confidence limit for 3 year RFS was >50%, we judged that the primary endpoint of this study was met.

Results: A total of 52 patients were enrolled between January 2016 and January 2019. Two patients were excluded from analysis; five patients were determined to have R1 or R2 resection, and seven patients did not receive adjuvant S-1. The 3-year RFS and overall survival rates in the intention-to-treat population were 72.3% (90% confidence interval [CI] 59.9-81.5) and 85.0% (90% CI 73.9-91.6), indicating that the primary endpoint was met. Grade ≥3 adverse events with an incidence ≥10% included neutropenia (13.2%), anorexia (13.2%), and diarrhea (10.5%). There were no treatment-related deaths.

Conclusion: Adjuvant S-1 after NAC-S showed promising efficacy with a manageable safety profile for patients with resectable ESCC and warrants further evaluation in larger studies.