[A Difficult Case of a Huge Cystic Gastrointestinal Stromal Tumor of the Stomach with CA125-Level Elevation].

A 67-year-old woman presented with abdominal distention. Computed tomography and magnetic resonance imaging revealed a huge tumor measuring >30 cm with solid and cystic regions. The serum level of CA125 was elevated. An exploratory laparotomy was performed by a gastroenterologist and a gynecologist for the purpose of diagnosis and tumor removal. During laparotomy, the ovary and uterus were found to be intact. The tumor was found to originate from the greater curvature of the stomach and invade the mesentery of the transverse colon. Histopathologically, tumor cells were positive on c-kit immunohistochemical staining. A high-risk gastrointestinal stromal tumor of the stomach was diagnosed according to the modified-Fletcher classification. Because cystic GIST is relatively rare and CA125 was elevated similar to that in Pseudo-Meigs syndrome, preoperative diagnosis was difficult in this case.