Angiomatoid features in fibrohistiocytic sarcomas. Immunohistochemical, ultrastructural, and clinical distinction from vascular neoplasms.

The typical example of malignant fibrous histiocytoma (MFH) or dermatofibrosarcoma protruberans (DFSP) does not require ancillary studies for diagnosis. However, hemorrhage with cystic change consisting of blood-filled spaces may closely mimic a vascular neoplasm. Eight fibrohistiocytic sarcomas exhibiting these angiomatoid features, initially mistaken for vascular neoplasms, were identified from personal consultation files and review of 157 consecutive sarcomas (1985 through 1993) at the University of California-(Davis) Medical Center. They included five MFH giant-cell-type sarcomas, two MFH angiomatoid-type sarcomas, and one DFSP. Immunohistochemical analysis of paraffin-embedded material showed vimentin diffuse positive, CD68 (KP-1) diffuse positive, and factor VIII negative in all eight sarcomas; actin HHF-45 focal positive in six, diffuse positive in one, and negative in one sarcoma; desmin focal positive in two and negative in six sarcomas; and S100 protein, cytokeratin AE1:AE3, cytokeratin 10.11, and EMA negative in all eight sarcomas. Electron microscopy of three tumors exhibited neoplastic cells with fibroblastic, myofibroblastic, and histiocytic features. Weibel-Palade bodies or neolumens diagnostic of vascular differentiation were absent. The clinical characteristics and behavior of these sarcomas reflect entities in the spectrum of fibrohistiocytic lineage (MFH subtypes and DFSP) rather than vascular neoplasms. Patients with deep, large, giant-cell-type MFHs did poorly (two of four patients died from disease at 8 and 25 months). Both patients with angiomatoid MFHs showed local recurrences from large incompletely excised head and neck lesions. One died of disease at 21 months and the other is free of disease 12 months following excision of a local metastasis to the opposite side of the neck. The patient with DFSP had an 18-cm locally recurrent scalp tumor that extended into bone. Immunohistochemical and ultrastructural confirmation of fibroblastic, myofibroblastic, and histiocytic lineage and exclusion of vascular differentiation help to establish the correct diagnosis in these fibrohistiocytic sarcomas with angiomatoid features. The clinicopathologic features of these eight cases reaffirm the practical utility of MFH and DFSP as diagnostic entities in the spectrum of fibrohistiocytic sarcomas.