786PPrimary results of multicenter phase II study of neoadjuvant chemotherapy with S-1 and oxaliplatin for locally advanced gastric cancer (Neo G-SOX PII)

399 Background: Prognosis for locally advanced gastric cancer (LAGC), such as clinical T4 disease, bulky nodal metastases, type 4 and large type 3 gastric cancer, was not satisfactory even by D2 gastrectomy followed by adjuvant chemotherapy. Neoadjuvant chemotherapy is another promising approach, therefore, we have conducted a phase II study to evaluate the efficacy and safety of the neoadjuvant chemotherapy of S-1 and oxaliplatin (G-SOX) followed by gastrectomy with D2/3 lymph node dissection for LAGC, and the primary endpoint of curative resection rate was met [Miki A, ESMO 2019]. We show longer follow-up data from this study. Methods: Patients with adenocarcinoma of the stomach; clinical T4; clinically resectable gastric cancer of type 4 or large type 3; bulky nodal involvement around major branched arteries to the stomach were enrolled. Patients receive two cycles of neoadjuvant chemotherapy with S-1 (80 mg/m2, p.o., days 1-14 followed by 1 week rest) and oxaliplatin (130 mg/m2 at day 1), followed by D2 or higher surgery with no residual disease. Patients with pathological R0/1 resection received S-1 (80 mg/m2, p.o., days 1-28 followed by 2 week rest) for 1 year as adjuvant chemotherapy. Primary endpoint was curative resection rate. Results: Between August 2015 and March 2017, forty-one patients were in enrolled. Of the patients, 39 patients (95%) completed the two courses of neoadjuvant chemotherapy of G-SOX, 37 (90%) received gastrectomy, and 36 (87.8%) received curative resection (R0/1). Grade 3 or higher toxicities during neoadjuvant chemotherapy of G-SOX were neutropenia (7%), fatigue (7%), diarrhea (5%) and thrombocytopenia (2%). No treatment related deaths were observed. Surgical complications including postoperative complications were observed in 13 patients (35%). Pathological response rate after neoadjuvant G-SOX was 40%. With a median follow-up period of 33.8 months, 3year-relapse free survival and 3year-ovearll survival was 54.3% and 73.1%, respectively. Conclusions: An update analysis confirmed that neoadjuvant chemotherapy of G-SOX is a feasible and might be one of the promising strategies for patients with LAGC. Clinical trial information: UMIN000018661.