Long-term outcomes of S-1 monotherapy in stage IIIA gastric cancer with small tumors and low nodal involvement

BackgroundIn Japan, adjuvant chemotherapy with docetaxel/S-1 is recommended for stage III gastric cancer. However, this regimen may not be suitable for all patients due to toxicity and tolerability issues, particularly in older individuals or those with comorbidities. This study aimed to explore prognostic factors in stage IIIA gastric cancer and assess long-term outcomes in patients treated with S-1 monotherapy after curative gastrectomy.MethodsWe retrospectively analyzed 73 patients with stage IIIA gastric cancer (UICC 7th edition) who underwent curative gastrectomy and received postoperative adjuvant S-1 monotherapy between 2005 and 2018.Various prognostic factors, including preoperative (age, sex, BMI, tumor markers), perioperative (surgical approach, operative duration, blood loss, complications), and tumor-related variables (tumor size, lymph node status, histological features), were analyzed. Recurrence-free survival (RFS) was the primary endpoint, and cut-off values were determined using ROC analysis. Cox proportional hazards models were used for univariate and multivariate analyses.ResultsThe 3- and 5-year RFS rates were 71.7% and 64.3%, respectively. Multivariate analysis identified smaller tumor size (<= 55.0 mm, P = 0.006) and lower lymph node positivity rate (<= 0.079, P = 0.008) as independent favorable prognostic factors.ConclusionS-1 monotherapy may be associated with favorable long-term outcomes in selected patients with stage IIIA gastric cancer who have small tumors and low lymph node positivity rates. While these results are encouraging, they should not be interpreted as a rationale for broadly recommending S-1 monotherapy. Further studies are needed to define its role in individualized treatment strategies.