What happened, in summary

A 70-year-old man presented with an abdominal mass and was found to have advanced gastric adenocarcinoma. CT showed extensive direct invasion into the abdominal wall and enlarged nearby lymph nodes, while no lung or liver metastases were seen. The gastric cancer was clinically Stage IV. The tumor was HER2-negative.

He received 6 courses of S-1 plus oxaliplatin chemotherapy. Imaging showed a partial response, with the abdominal-wall invasion becoming smaller. This reduction made a complete operation more feasible.

Surgeons then performed distal gastrectomy with D2 lymph-node dissection together with en-bloc removal of the involved transverse colon and abdominal wall. Clear surgical margins were achieved. Postoperative pathology still showed invasion into the rectus abdominis muscle and lymph-node involvement, but the pathologic stage was Stage III after chemotherapy. Two months after surgery, he started adjuvant S-1 chemotherapy.

At 6 months after the operation, CT showed no recurrence. The chemotherapy response had made radical resection possible despite the tumor's extensive abdominal-wall invasion.