Background: Neoadjuvant chemotherapy followed by surgery (NAC-S) represents the standard treatment for patients with Stage II/III esophageal squamous cell carcinoma (ESCC) in Japan. Chemoradiotherapy (CRT) is performed in patients who refuse or have contraindications to surgery. However, randomized clinical trials that compare NAC-S with CRT have not been conducted. The aim of this study was to explore subgroups of patients undergoing CRT to identify those with survival outcomes potentially equivalent to NAC-S. Methods: Pooled data from two clinical trials in patients with Stage II/III ESCC, the JCOG9907 trial and the JCOG9906 trial were used. JCOG9907 demonstrated that NAC-S resulted in superior overall survival (OS) compared with surgery followed by adjuvant chemotherapy. JCOG9906 was a single-arm trial that explored the efficacy and safety of CRT. The eligibility criteria in the two trials were almost identical. Subgroup analyses of clinical data (serum albumin, cT, cN, cstage and tumor location) were conducted with Cox proportional hazards regression models for patients assigned to receive NAC-S in JCOG9907 and patients in JCOG9906. Results: The analysis comprised 163 patients from JCOG9907 in NAC-S arm (NAC-S group) and 73 patients from JCOG9906 who received CRT (CRT group). Baseline characteristics were similar between the two groups. OS was better in the NAC-S group than the CRT group (adjusted hazard ratio 1.72; 95% confidence interval 1.19-2.50). All subgroups in the NAC-S group had longer OS compared with those in the CRT group. Conclusions: OS was superior after NAC-S rather than CRT. None of the CRT subgroups had similar OS to the NAC-S groups.
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