title: Malignant fat-forming solitary fibrous tumor (so-called "lipomatous hemangiopericytoma"): clinicopathologic analysis of 14 cases.
abstract: Fat-forming solitary fibrous tumor is a rare variant of solitary fibrous tumor (SFT). Generally regarded as benign, very few fat-forming SFTs with malignant histologic features have been reported. Here, we report 14 histologically malignant fat-forming SFTs to better characterize this subset. Seven patients were female and 7 were male, with ages ranging 20 to 93 years (median, 57 y). Five tumors were located in the lower limb, 3 in the trunk, 3 in abdominopelvic locations, 2 in the head and neck region, and 1 in the upper limb. The tumor size ranged from 3.4 to 20 cm (median, 8.6 cm). Histologically, all exhibited at least focal hypercellularity; 12 tumors had mitoses >4/10 high-power fields (range, 2 to 37; median, 8), 12 showed at least moderate atypia, and 8 showed necrosis. It should be noted that 7 tumors contained only mature adipose tissue, whereas 5 contained multivacuolated lipoblasts and 2 had areas resembling atypical lipomatous tumor (ALT). Immunohistochemically, CD34 and CD99 were positive in most cases (11 of 14 and 8 of 10, respectively); MDM2 and CDK4 were both negative in all 4 cases tested (including both tumors with ALT-like areas). Follow-up data from 10 cases (median duration, 47.5 mo; range, 5 to 76) showed 2 patients with multiple metastases (both to lung and bones, and 1 each to breast and to soft tissue), both of whom died of disease. In conclusion, fat-forming SFTs exhibiting malignant histologic features have potential for aggressive behavior. The presence of lipoblasts and/or ALT-like areas, although described in some "benign" examples of fat-forming SFT, seems much more common in the malignant subset and may prompt a careful search for morphologic evidence of malignancy in any case of fat-forming SFT.
authors.affiliation: Department of Pathology, National Taiwan University Hospital, Medical College, National Taiwan University, Taipei, Taiwan.
authors.forename: Jen-Chieh
authors.initials: JC
authors.lastname: Lee
authors.forename: Christopher D M
authors.initials: CD
authors.lastname: Fletcher
mesh_terms: D000008:Abdominal Neoplasms / Q000737:chemistry / Q000401:mortality / Q000473:pathology* / Q000628:therapy; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D014408:Biomarkers, Tumor / Q000032:analysis; D001706:Biopsy; D005121:Extremities; D005260:Female; D006258:Head and Neck Neoplasms / Q000737:chemistry / Q000401:mortality / Q000473:pathology* / Q000628:therapy; D006393:Hemangiopericytoma / Q000737:chemistry / Q000401:mortality / Q000473:pathology* / Q000556:secondary / Q000628:therapy; D006801:Humans; D007150:Immunohistochemistry; D008067:Lipoma / Q000737:chemistry / Q000401:mortality / Q000473:pathology* / Q000628:therapy; D008297:Male; D008875:Middle Aged; D012004:Rectal Neoplasms / Q000737:chemistry / Q000401:mortality / Q000473:pathology* / Q000556:secondary / Q000628:therapy; D012983:Soft Tissue Neoplasms / Q000737:chemistry / Q000401:mortality / Q000473:pathology* / Q000628:therapy; D054364:Solitary Fibrous Tumors / Q000737:chemistry / Q000401:mortality / Q000473:pathology* / Q000556:secondary / Q000628:therapy; D013997:Time Factors; D016896:Treatment Outcome; D055815:Young Adult
chemical_list: D014408:Biomarkers, Tumor