[A Case of a Desmoid Tumor the Developed Around Ileostomy in a Patient with FAP].

A 21-year-old woman who underwent laparoscopic total colectomy for familial adenomatous polyposis (FAP) 1 year 3 months previously presented with a mass larger than 10 cm around the ileostomy. Multiple tumors in the mesentery around the ileostomy and anterior to the sacrum, accompanied by bilateral hydronephrosis, were detected by computed tomography. The patient was diagnosed with intraabdominal desmoid tumors, stage Ⅳ according to the Church's classification. The desmoid tumor (15×9 cm) around the ileostomy was completely resected surgically, whereas another desmoid tumor (5×4 cm) was incompletely resected. We found a desmoid tumor of more than 10 cm in size and many fibromatous plaques in the mesentery. We then performed 4 courses of systemic chemotherapy with dacarbazine and doxorubicin in for the residual desmoid tumors after surgery. There was no growth of the residual desmoid tumors for 12 months after chemotherapy. Genetic tests detected a pathogenic germline mutation of the APC gene in the high-risk region of the desmoid tumor. We also confirmed somatic mutations in the resected specimens.