malignant fat-forming solitary fibrous tumor
Definition: 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.
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.
Synopsis
Sex ratio: 1/1
Age ranging 20 to 93 years (median, 57 y)
location: lower limb, trunk, abdominopelvic locations, head and neck region, upper limb
Tumor size : from 3.4 to 20 cm (median, 8.6 cm).
focal hypercellularity
mitoses >4/10 high-power fields (range, 2 to 37; median, 8)
at least moderate atypia
necrosis
about 40% of tumors contained only mature adipose tissue
some contain multivacuolated lipoblasts
rare areas resembling atypical lipomatous tumor (ALT).
Immunohistochemistry
CD34 and CD99 positive in most cases
MDM2 and CDK4 both negative in all cases tested
Prognosis
possible multiple metastases (lung and bones, breast and soft tissue).
References
Malignant Fat-Forming Solitary Fibrous Tumor (so-called "Lipomatous Hemangiopericytoma"): Clinicopathologic Analysis of 14 Cases. Lee JC, Fletcher CD. Am J Surg Pathol. 2011 Jun 29. PMID: #21716088#