Adjuvant chemoradiotherapy plus pembrolizumab for locally advanced esophageal squamous cell carcinoma with high risk of recurrence following neoadjuvant chemoradiotherapy: a single-arm phase II study

Background: Adjuvant nivolumab reduces recurrence in patients with locoregional esophageal cancer who had pathological residual disease after neoadjuvant chemoradiotherapy and R0 resection. However, the efficacy of adjuvant anti-PD-1 therapy in patients at higher risk of recurrence remains unclear. Methods: This phase II trial (ClinicalTrials.gov identifier: NCT03322267) enrolled patients with locally advanced esophageal squamous cell carcinoma (ESCC) received neoadjuvant chemoradiotherapy plus esophagectomy but still had various risk factors for recurrence, such as involved or close margins (≤ 1 mm), extranodal extension of the involved lymph nodes, and the ypN2-3 stage. Patients received adjuvant therapy composed of a course of cisplatin-based chemoradiotherapy and pembrolizumab (200 mg, IV every 3 weeks) for 18 cycles. The primary endpoint was 1-year relapse-free survival (RFS) rate. Results: Twenty-five patients were enrolled. The risk factors were tumor margins of ≤ 1 mm (18 patients), extranodal extension of the involved lymph nodes (9 patients), and the ypN2-3 stage (9 patients). The median follow-up duration was 21.6 months (95% CI: 18.7–33.2). The rate of 1-year RFS was 60.0%. The median duration of RFS and overall survival was 14.3 (95% CI: 9.0–19.5) and 21.6 (95% CI: 0.0–45.5) months, respectively. Treatment-emergent adverse events of any grade and those of ≥ 3 grade occurred in 56% and 8% of all patients receiving cisplatin-based chemoradiotherapy and in 79.2% and 12.5% of those receiving pembrolizumab. Conclusions: Adjuvant chemoradiotherapy followed by pembrolizumab is feasible and may be associated with improved 1-year RFS rate in patients at high risk of recurrence after trimodality therapy for locally advanced ESCC. Trial registration number ClinicalTrials.gov (No. NCT03322267).