Comparison Between Upfront Surgery and Preoperative Chemotherapy for <scp>CY1P0</scp> Gastric Cancer: A Japanese Sub‐Analysis of <scp>CONVO</scp> ‐ <scp>GC</scp> ‐1

ABSTRACT Background Radical gastrectomy, followed by adjuvant chemotherapy has been a common practice in Japan for peritoneal lavage cytology‐positive (CY1) but peritoneal dissemination‐negative (P0) stage IV gastric cancer. This study aimed to clarify the differences in treatment outcomes between upfront surgery and preoperative chemotherapy, followed by surgery for patients with CY1P0 gastric cancer using data from Japanese patients recruited for the CONVO‐GC‐1 study. Methods This study used data from Japanese patients with CY1P0 gastric cancer recruited for the international retrospective observational CONVO‐GC‐1 study. Gastrectomy was performed between January 1, 2001, and December 31, 2014. CY1 was cytologically confirmed. The patients were divided into two groups: upfront surgery (Sx) and preoperative chemotherapy, followed by surgery (CSx). Patient background and survival outcomes were compared between the groups. Results Four hundred and thirty‐three patients treated at 45 Japanese institutions were analyzed. There were 306 and 127 patients in the Sx and CSx groups, respectively. The 5‐year overall survival (OS) rates were 19.2% in the Sx group and 35.9% in the CSx group, with a significant difference. When stratifying OS of the two groups by residual tumor status, the 5‐year OS rates were 43.0% in the CSx‐R0 group, 14.9% in the CSx‐R1 group, 20.7% in the Sx‐R1 group, and 0.0% in the CSx‐R2 and Sx‐R2 groups. Conclusions In CY1P0 gastric cancer, survival was better with preoperative chemotherapy, followed by surgery than with upfront surgery. Survival was particularly favorable in patients who underwent R0 resection.