[A case of undifferentiated gastric cancer that recurred with portal vein tumor thrombus].

A 69-year-old man with a malignant tumor of the stomach underwent distal gastrectomy with partial resection of the abdominal wall, transverse colon, and lateral segment of the liver. Based on a detailed pathological examination of the resected specimen, a diagnosis of undifferentiated gastric cancer was established. Six months after the operation, during postoperative adjuvant chemotherapy with S-1, diagnostic imaging, including CT and positron emission tomography (PET), revealed a portal vein tumor thrombus and diffusely spreading metastases in the posterior segment of the liver. Despite chemotherapy with S-1/CDDP, the metastatic tumors continued to grow rapidly. The patient died 10 months after the operation. On autopsy, the portal vein tumor thrombus was observed to be composed of undifferentiated cancer cells invading into the liver parenchyma through hepatic sinusoids, with the metastatic tumors replacing 60% or more of the entire liver.