S-1 adjuvant chemotherapy: 4 or 8 courses in stage 2 gastric cancer?

The final follow-up data of the primary outcome of the phase 3 OPAS-1 trial suggested that 8 courses of S-1 adjuvant chemotherapy is the preferred option over 4 courses of this treatment regimen in patients with stage 2 gastric cancer who underwent resection.

The OPAS-1 trial (UMIN000007306) compared the standard-of-care treatment for patients with pathological stage 2 gastric cancer who underwent D2 gastrectomy, which is 8 courses of S-1 adjuvant chemotherapy, to a shortened version of this therapy, namely 4 courses [1]. In total, 590 patients were randomised to one of the 2 study groups. At the first interim analysis, the study was closed due to futility and it demonstrated that 4-courses of S-1 led to slightly inferior results in terms of relapse-free survival (RFS) compared with 8 courses [2]. Dr Souya Nunobe (Cancer Institute Hospital, Japan) presented the updated results of the trial.

The 5-year RFS rates displayed a slight numerical benefit for patients who had received 8 courses of S-1 compared with those who had received only 4 courses of this therapy (87.7% vs 85.6%; HR 1.27; 95% CI 0.85–1.89). The 5-year overall survival rates were 89.7% in the standard-of-care arm and 88.6% in the experimental arm (HR 1.12; 95% CI 0.72–1.75).

According to Dr Nunobe, 8 courses of S-1 adjuvant chemotherapy is highly recommended in Japanese guidelines in patients with pathological stage 2 gastric cancer.

1. Nunobe S, 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). Abstract 381, ASCO GI 2023, 19–21 January, San Francisco, CA, USA.
2. Yoshikawa T, et al. Annals of Oncology. 2017;28(5):V214.

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