Safety and effectiveness of pembrolizumab combined with paclitaxel and cisplatin as neoadjuvant therapy followed by surgery for locally advanced resectable (stage III) esophageal squamous cell carcinoma: a study protocol for a prospective, single-arm, single-center, open-label, phase-II trial (Keystone-001)

Background: Esophageal squamous cell carcinoma (ESCC) is one of the most refractory malignant tumors. Esophageal cancer (EC) is a malignant tumor with a high incidence worldwide, and over 50% of EC cases occur in China. Under the National Comprehensive Cancer Network (NCCN) guidelines, concurrent chemoradiotherapy is the only standard neoadjuvant treatment for locally advanced ESCC. In the first-line treatment of advanced ESCC, the efficacy of immune checkpoint inhibitors (ICIs) combined with systemic chemotherapy is significantly better than that of chemotherapy alone. Paclitaxel and cisplatin (TP), as one of the neoadjuvant chemotherapy regimens for locally advanced ESCC, have been widely used in China in recent years. ICIs combined with TP as neoadjuvant therapy seems promising. Methods: This is an open-label, single-arm, single-center, phase-II trial. Locally advanced resectable (stage III) ESCC patients who have not undergone previous systemic treatments will be enrolled in this study. All the subjects will intravenously receive 3 cycles of pembrolizumab (200 mg) on day 1, paclitaxel (135 mg/m(2)) on day 2, and cisplatin (20 mg/m(2)) on days 2-4, every 3 weeks. After an efficacy evaluation, the subjects will undergo Da Vinci robot-assisted radical resection. If the postoperative pathologic results do not reveal a complete response, pembrolizumab will be administrated for at least 6 cycles as an adjuvant therapy with the same usage as before. The primary endpoints are the major pathological response and safety. The secondary endpoints include the objective response rate (ORR), overall survival (OS), disease-free survival (DFS), the R0 resection rate, and perioperative complications. The exploratory endpoint is to examine the correlation between related biomarkers and tumor responses to this neoadjuvant treatment regimen. Discussion: This trial is the first enrolled study to evaluate the safety and efficacy of pembrolizumab combined with TP as neoadjuvant therapy for locally advanced ESCC. Currently, under the NCCN guidelines, neoadjuvant chemoradiotherapy (nCRT) is the only recommended treatment for locally advanced ESCC. This phase-II study will provide preliminary evidence of the efficacy of pembrolizumab combined with TP as novel neoadjuvant therapy for patients with locally advanced ESCC.