CO-STAR: Surgical Conversion Feasibility Trial of Sintilimab (PD-1 Inhibitor) Combined with Nab-PTX, S-1 and Apatinib for the First-Line Treatment of Stage IV Gastric Cancer (GC).

e16041 Background: Chemotherapy and PD-1 inhibitor have shown significant clinical benefits in first-line treatment of GC, overall survival was still dismal. The surgical intervention with curative or life prolonging intention was evaluated as feasible for stage IV GC from clinical trials and retrospective cohorts. Our previous study of cytotoxic chemotherapy (S-1 & PTX) in combination with multi-targets anti-angiogenic TKIs illustrated increased response and R0 resection rate. Given the enhanced response from chemo, PD-1 and TKIs regimens, this trial was designed to assess the feasibility of surgical conversion from this combination in stage IV GC. Methods: This is a prospective, single-arm, single-center, phase II trial. Eligible criteria were treatment naïve, histopathologically confirmed stage IV (AJCC8th) and ECOG PS 0-1 GC adenocarcinoma. Pts were given with sintilimab (200mg, iv, d1) combined with Nab-PTX (w/o peritoneal spread: 260 mg/m2, iv, d1; w/ peritoneal spread: 180 mg/m2, iv, d1 and 80 mg/m2, ip, d1), S-1 (60mg, po, bid, d1-14), and apatinib (250mg, po, qd) every 3 wks. Tumor response was assessed every 2-4 cycles by radiologic imaging and MDT was employed to determine surgical feasibility. Safety run-in was employed in the first 3+3 pts by DLTs to determine the tolerability. The primary endpoint was ORR and R0 surgical conversion rate. Results: 42 pts were enrolled up to 2/2021. The median follow-up was 3.5m (range 0.7-11.3). The median age was 56 yrs (range 31-72), male was 47.6%, and PS 1 was 31.0%. The metastatic factors were characterized as No.16 lymph nodes 54.8% (23), liver 23.8% (10), peritoneum 40.5% (17), Krukenberg 2.4% (1), and extensive metastases (≥2 organs) 42.9% (18). No DLT occurred in initial 6 pts. Of 36 evaluable pts, ORR was 61.1% and DCR was 97.2%. Surgical conversion was currently identified in 18 pts with 94.4% (17) R0 resection, and the R0 surgical conversion rate was 47.2% (17/36). Median treatment cycle in converted pts was 4. 22.2% (4/18) pts achieved pathological complete response (TRG 0), and 27.8% (5/18) pts had major response (TRG 0-1). The most common AEs were grade 1-2, and 1 SAE of hemorrhage grade 4 occurred. No increase of anastomotic leakage, hemorrhage, and abdominal infection, and no surgery caused death and complication caused second operation occurred. The median postoperative length of stay was 9.5d (range 6-16). Conclusions: These preliminary results showed favorable tumor response and acceptable tolerability for potential surgical resection. Sintilimab, doublet chemotherapy, and apatinib might offer an opportunity of cure for stage IV gastric cancer. Trial ID: NCT04267549. Clinical trial information: NCT04267549. [Table: see text]