Phase II study of SHR1210 and trastuzumab in combination with CAPOX for neoadjuvant treatment of HER2-positive gastric or gastroesophageal junction (GEJ) adenocarcinoma.

296 Background: Perioperative treatments have significantly improved survival in patients with resectable gastric cancer. PANTHERA study had showed a significant tumor shrinkage for HER2 positive advanced gastric cancer treated with anti-PD-1 agent, transtuzumab and chemotherapy. SHR1210, a human IgG4 monoclonal antibody that binds to PD-1, has shown remarkable clinical efficacy in various cancers. We aimed to assess the activity and safety profile of the addition of SHR1210 and trastuzumab to CAPOX for neoadjuvant treatment of HER2-positive gastric or GEJ adenocarcinoma. Methods: In this ongoing, single-arm, phase II study, we recruited patients from Henan Cancer Hospital in China with histopathologically diagnosed resectable HER2-positive gastric or GEJ adenocarcinoma who had clinical T3/N+ or higher stage. Patients were given 4 cycles of transtuzumab (loading dose of 8mg/kg, with subsequent doses of 6 mg/kg, q3w) and CAPOX (oxaliplatin 130 mg/m 2 day 1, capecitabine 1000 mg/ m 2 bid po day 1-14, q3w) in combination with 3 cycles of SHR1210 (200mg, iv, d1, q3w), followed by surgery and 4 postoperative cycles of CAPOX. The primary endpoint was pathological complete response (pCR). The secondary endpoints included major pathological remission (MPR) and objective response rate (ORR). This trial is registered with ClinicalTrials.gov, number NCT03950271. Results: Between Jan 20, 2020, and Sept 15, 2021, 22 patients were enrolled and commenced treatment. Four patients had not completed neoadjuvant treatment. Twopatitents refused surgery. Sixteen patients who experienced D2 resection, 9 (56.3%) achieved MPR, including 5 (31.3%) with pCR (ypT0N0M0). The R0 rese-ction rate was 100%. The ORR was 77.3%. The main grade 3 or 4 treatment-related adverse events (TRAEs) included lymphocytopenia (22.7%), neutropenia(13.6%), thrombocytopenia (13.6%) and anaemia (5%). Most frequent grade 1 or 2 TRAEs were Nausea (68.2%), lymphocytopenia (63.6%), leukopenia (59.1%), Anaemia (59.1%), Thrombocytopenia (50%), Serum aspartate aminotransfe-rase increased (45.5%) and hypothyroidism (31.8%). There was no surgical del-ays or unexpected surgical complications related to drug toxicity. Conclusions: Neoadjuvant combination of SHR1210, transtuzumab and CAPOX is a safe and efficacious treatment option for patients with HER2-positive gastric or GEJ adenocarcinoma. More importantly, 31.3% pCR rate is encouraging. Our clinical study is still enrolling, and the survival effects are under follow up. Clinical trial information: NCT03950271.