A case of a malignant fat-forming solitary fibrous tumor of the abdominal wall

Background : We report herein on the cytological findings in a case of a malignant fat-forming solitary fibrous tumor (MFFSFT) of the abdominal wall. Case : A woman in her 70 s with a hepatic hemangioma had been followed up only, but an operation was deemed necessary because of increase of the tumor size and the possibility of a metastatic lesion in the liver. Smear cytology of the primary and metastatic tumors showed many atypical spindle and oval tumor cells with variation in the nuclear size and shape, and pleomorphism against a necrotic background. Large perivascular tumor cell clusters containing fat cells were also observed. Immunohistochemically, tumor cells were positive for CD34, bcl-2, and CD99. A histological diagnosis of MFFSFT was made. Conclusion : In cytology, when perivascular tumor cell clusters are observed that may correspond to the histological features of a hemangiopericytomatous pattern with fat cells, in addition to conspicuous nuclear atypia, necrosis, and mitotic activity, MFFSFT should be considered in the differential diagnosis.