AB37. Current situation and issues of conversion therapy for stage IV gastric cancer

Abstract: Conversion therapy on stage IV gastric cancer (GC) patients has been paid much attention recently and it can be defined as surgical treatment aiming at R0 resection after successful chemotherapy, originally unresectable or marginally resectable tumors, technically and/or oncologically. Although the prognosis of stage IV GC has been improving recently with new chemotherapeutic and molecular targeting agents, it is not still satisfactory. With the development and improved response of the chemotherapy regimens, much approaches on conversion therapy for stage IV GC has been successfully demonstrated. However, there is no evidence regarding the benefit of conversion therapy in stage IV GC. To clarify the meaning of surgical intervention for advanced GC, we retrospectively analyzed 63 stage IV GC patients treated with S-1/CDDP or S1/TXT. Median survival time (MST) of all patients was 16.5 months and there was no significant difference of MST between the group of S-1/CDDP and S-1/TXT. Twenty-seven patients underwent gastrectomy and severe perioperative complications were not observed. Among the patients that showed response to chemotherapy, MST was extended in the patients who underwent gastrectomy. It is suggested that S-1 based chemotherapy combined with conversion therapy (adjuvant surgery) for stage IV GC showed acceptable results and it performed safely. We also examined the efficacy of chemotherapy after conversion therapy in stage IV GC patients. MST of all stage IV patients with conversion therapy was 31.2 months and MST after conversion therapy was 12.5 months. There was no difference in MST between those who had S1 monotherapy and doublet (combination) therapy. Thirty-six out of 49 patients had relapse and 31 had 2^nd line chemotherapy after conversion. RFS of the patients with 2^nd line chemotherapy was longer than that of those with only 1^st line chemotherapy. In conclusion, further study is needed to confirm the survival benefit of adjuvant surgery. We are now performing the phase II cohort study of gastrectomy after S-1 based chemotherapy for stage IV GC patients. Furthermore, large scale retrospective and prospective cohort study are being conducted now in Asian countries based on Federation of Asian Clinical Oncology (FACO) consisted of Japanese Society of Clinical Oncology (JSCO), Korean Association of Clinical Oncology (KACO) and Chinese Society of Clinical Oncology (CSCO), supported by Japanese Gastric Cancer Association (JGCA), Korean Gastric Cancer Association (KGCA) and Gastric Cancer Association of Chinese Anti-cancer Association.