[A Case of Unresectable Advanced Gastric Cancer Successfully Treated with Conversion Surgery].

A man in his 70s consulted a local clinic with a chief complaint of difficulty eating. Upper gastrointestinal endoscopy revealed a type 4 tumor spreading irregularly from immediately below the esophageal cardia to the lower gastric body. The patient was referred to our hospital with a diagnosis of advanced gastric cancer(human epidermal growth factor receptor 2 [HER2]-positive moderately-differentiated adenocarcinoma)accompanied by lymph node enlargement. We planned an open total gastrectomy after staging laparoscopy to rule out dissemination because peritoneal dissemination could not be ruled out using computed tomography(CT). To perform a total gastrectomy, a celiotomy was done after staging laparoscopy results suggested that dissemination was unlikely. However, the border between the pericardial lymph nodes and the pancreas or peritoneal artery was not visible, forcing us to terminate the staging laparotomy based on a judgment of unresectable locally advanced gastric cancer. Therefore, the patient was administered 6 cycles of combined S-1/CDDP plus trastuzumab as the primary therapy. The response to therapy was favorable, and we scheduled a surgical resection. However, the scheduled surgery was rescheduled because of COVID-19 pneumonia, and R0 resection was finally performed after the 7th cycle of S-1/CDDP plus trastuzumab therapy. Histopathologically, the regional lymph node metastasis had disappeared, the viable tumor remained within the mucosal layer, and scarring was evident from the submucosal layer to the serosa. In recent years, conversion surgery for unresectable gastric cancer has been sporadically reported. However, we are unable to definitively opine on whether this kind of surgery may contribute to improving the prognosis, resection remains indispensable for radical treatment. We report this case along with a review of the literature.