Efficacy and Safety of Sintilimab in Combination with Concurrent Chemoradiotherapy for Locally Advanced Gastric or Gastroesophageal Junction (GEJ) Adenocarcinoma (SHARED): Study Protocol of a Prospective, Multi-Center, Single-Arm Phase 2 Trial

Purpose: Concurrent chemoradiotherapy (cCRT) is the mainstay therapy of locally advanced gastric (G) and gastroesophageal junction (GEJ) cancers with a poor prognosis. Programmed cell death receptor-1 (PD-1) inhibitor has been approved and recommended to treat >= 3 line G/GEJ patients. A significant clinical benefit of PD-1 inhibitors in addition to cCRT has been observed in locally advanced lung cancer. Sintilimab, a humanized IgG4 monoclonal antibody with high affinity and specificity for PD-1, has shown promising efficacy with an overall response rate of 85% in combination with chemotherapy in gastric cancer in a phase Ib study (NCT02937116). Patients and Methods: SHARED is a prospective, multicentre, single-arm Phase II trial in China, exploring the efficacy of sintilimab in combination with cCRT in locally advanced G/GEJ adenocarcinoma. According to a Simon optimal two-stage clinical design, 34 patients will be enrolled. All the eligible patients will receive one cycle of induction chemotherapy (S-1 plus nab-PTX) combined with sintilimab, followed by cCRT (radiotherapy plus nab-PTX) combined with sintilimab. Prior to the surgery, patients will receive another cycle of chemotherapy (S-1 plus nab-PTX) combined with sintilimab. In the adjuvant setting, all participants will be treated with 3 cycles of chemotherapy (S-1 plus nab-PTX) combined with sintilimab. The primary endpoint is the rate of pathological complete response (pCR). The secondary endpoints include disease-free survival (DFS), major pathological response (MPR), R0 resection rate, surgical AEs, overall survival (OS), event-free survival (EFS), and safety profile. Moreover, the prognostic value of tumor biomarkers and immune biomarkers will be explored. Conclusion: SHARED is designed to primally evaluate the efficacy and safety of sintilimab in combination with cCRT in locally advanced G/GEJ cancers and to prospectively validate the prognostic value of tumor biomarkers and immune biomarkers.