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.

Abstract

123 Background: 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: A total of 110 patients were collected. Of the 94 eligible patients, 84 patients underwent gastrectomy followed by Post-Cx with S-1 (S-1 group: n = 55), SP (SP group: n = 22) or others (Others group: n = 7), and 10 patients did not receive post-Cx (non-Cx group). Median age for the S-1, SP, Others and non-Cx groups were 66, 60, 61, and 79 years old. Sites of oligo-metastasis (HEP/LYM) was 21/34, 9/13, 2/5, and 7/3 in the S-1, SP, Others and non-Cx groups. The 3- / 5-year overall and relapse free survival (OS and PFS) rates of all the patients were 45.6/31.4% and 24.5/21.3%, respectively. Median OS was 28.5 and 36.5 months in the S-1 and SP groups (HR 0.99; 95% CI 0.54-1.82, p = 0.986). In multivariate analysis, no Post-Cx, over 70 years old were identified as the independent poor prognostic factor for OS (p < 0.05). Conclusions: R0 resection followed by Post-Cx for GC patients with O-Meta showed favorable survival, while there seems no additional benefit of cisplatin to S-1 alone.