Comparison between S-1 monotherapy and S-1 plus cisplatin as postoperative chemotherapy after R0 resection for stage IV gastric cancer patients with oligometastasis: A multicenter retrospective study.

123Background: Gastric cancer (GC) with liver metastasis (M1: HEP) and para-aortic lymph node metastasis (M1: LYM) is categorized as stage IV. Based on the retrospective reports, surgical resection is weakly recommended for oligo-metastasis (O-Meta), if resectable, in the Japanese GC Treatment Guidelines 2018. Whereas S-1 monotherapy as adjuvant chemotherapy after surgery for stage II/III GC and S-1 plus cisplatin (SP) as palliative chemotherapy for unresectable stage IV GC are standard treatments, there is no consensus about post-operative chemotherapy (Post-Cx) after R0 resection of stage IV GC with O-Meta. Methods: The criteria for this retrospective study were: 1) no prior treatment for GC, 2) R0 resection including O-Meta (HEP or LYM) at 20 institutions in the Stomach Cancer Group of the Japan Clinical Oncology Group between 2007 and 2012, 3) histological confirmation of adenocarcinoma for primary tumor and O-Meta (M1: HEP or LYM), 4) no other distant metastasis such as peritoneal metastasis. Results...