A full year of adjuvant S-1 chemotherapy is “highly recommended” for patients with stage II gastric cancer, according to a presentation at the 2023 ASCO Gastrointestinal Cancers Symposium.1

The final analysis of the phase 3 OPAS-1 trial showed that 6 months of S-1 chemotherapy was inferior to 1 year of the treatment. At the 5-year follow-up, the relapse-free survival (RFS) and overall survival (OS) rates were inferior among patients who received the shorter course of therapy.

The OPAS-1 trial included 590 patients with stage II gastric cancer who were randomly assigned to receive adjuvant S-1 chemotherapy for 6 months (4 courses; n=295) or 1 year (8 courses; n=295). In both arms, 1 course of treatment consisted of S-1 at 80 mg/m2 for 4 weeks, followed by a 2-week rest period. Prior to receiving S-1, all patients had R0 resection via gastrectomy with D1-plus or D2 lymph node dissection.

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At the first interim analysis in 2017, this trial was terminated due to futility, explained study presenter Souya Nunobe, MD, PhD, of Cancer Institute Hospital in Tokyo, Japan. Data at that time showed inferior RFS with 4 courses of S-1.2 Dr Nunobe presented the final 5-year analysis showing similar results.1

Dr Nunobe noted that 27 patients allocated to the 4-course arm were still receiving S-1 when the study closed. Of those patients, 22 decided to receive 8 total courses of S-1.

At a median follow-up of 5.8 years, RFS and OS were inferior with 4 courses. The 5-year RFS rate was 85.6% with 4 courses and 87.7% with 8 courses (hazard ratio [HR], 1.265; 95% CI, 0.846-1.892). The 5-year OS rate was 88.6% with 4 courses and 89.7% with 8 courses (HR, 1.121; 95% CI, 0.719-1.749).

“S-1 adjuvant chemotherapy for 1 year or 8 courses is highly recommended for pathological stage II gastric cancer,” Dr Nunobe concluded.

Disclosures: Some study authors declared affiliations with biotech, pharmaceutical, and/or device companies. Please see the original reference for a full list of disclosures.


1. Nunobe S, Yoshikawa T, Nishida Y, et al. Five-year follow-up results of a randomized phase III trial comparing 4 and 8 courses of S-1 adjuvant chemotherapy for pathological stage II gastric cancer: JCOG1104 (OPAS-1). ASCO GI 2023. January 19-21, 2023. Abstract 381.

2. Yoshikawa T, Terashima M, Mizusawa J, et al. Four courses versus eight courses of adjuvant S-1 for patients with stage II gastric cancer (JCOG1104 [OPAS-1]): An open-label, phase 3, non-inferiority, randomised trial. Lancet Gastroenterol Hepatol. 2019 Mar;4(3):208-216. doi:10.1016/S2468-1253(18)30383-2