Efficacy and safety of toripalimab combination with SOX regimen as a first-line treatment in patients with unresectable locally advanced or recurrent/metastatic gastric/gastroesophageal junction cancer: Preliminary data from a single-armed, exploratory study.

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e16015 Background: Gastric cancer (GC) is one of the most common malignancies of the digestive system with a poor prognosis and limited treatment option. Currently immunotherapy is approved for the third-line treatment of GC, but there are limited data on first-line treatment. Therefore, this study will further explore the efficacy and safety of the domestic PD-1 antibody toripalimab combined with S-1 plus oxaliplatin (SOX) regimen as the first-line treatment of unresectable locally advanced or recurrent/metastatic gastric/gastroesophageal junction cancer. Methods: A prospective, single-armed, exploratory, investigated initiated trial explores the efficacy and safety of toripalimab combined with SOX regimen as first-line treatment of unresectable locally advanced or recurrent/metastatic gastric/gastroesophageal junction cancer. The primary objectives are objective response rate (ORR). Secondary objectives include disease control rate (DCR), DOR, PFS, and OS. The dosage regimen is: Toripalimab, 240mg D1; oxaliplatin, 130mg/m2, D1 ; S-1, 40mg/m2, bid oral D1-14 days, every 21 days as a cycle and plan 6 cycles of treatment. Tumor responses were assessed radiologically every two cycles. Major eligibility requirements include: unresectable advanced, recurrent or metastatic gastric/gastroesophageal junction cancer with diagnoses confirmed histologically or cytologically, age 18 and 80 years, first-line treatment, at least one measurable lesion according to RECIST 1.1, ECOG 0-1, adequate organ function and HER-2 negative. Results: So far, 17 of planned 20 patients have been enrolled. 14 patients completed 2 cycles of treatment, the ORR rate was 57% (8/14) and the disease control rate (DCR) was 93% (13/14). 10 patients completed 4 cycles of treatment, the ORR rate was 60% (6/10) and the disease control rate (DCR) was 90% (9/10). 7 patients completed 6 cycles of treatment, the ORR rate was 43% (3/7) and the disease control rate (DCR) was 57% (4/7). Common adverse reactions during treatment in 17 patients included rash 17.6% (3/17), diarrhea 41.2% (7/17), hypothyroidism 11.8% (2/17), elevated amylase 35.3% (6/17), decreased platelets 41.2% (7/17), mostly grade I-II. Conclusions: Toripalimab combination with SOX regimen as a first-line treatment demonstrated promising anti-tumor activity in unresectable locally advanced or recurrent/metastatic gastric/gastroesophageal junction cancer patients with a good ORR and controllable safety. Clinical trial information: NCT04202484.