OBJECTIVETo study the clinicopathologic features, immunophenotype, molecular genetics and differential diagnosis of solid variant of angiomatoid fibrous histocytoma.

METHODSThe clinicopathologic features of 3 cases of solid variant of angiomatoid fibrous histocytoma were analyzed and the literature was reviewed.

RESULTSThere were a total of 2 males and 1 female. The age of patients ranged from 9 to 12 years. The patients presented with a painless mass located in left forearm, left knee or back. The lesions were treated by complete surgical resection. On gross examination, the tumors varied from 1.6 cm to 4.5 cm in greatest dimension. They were well-circumscribed and had pale yellow to grayish-red solid cut surface. Histologically, the tumor was composed of histocytoid cells arranged in sheet-like pattern. A fibrous pseudocapsule surrounded by lymphocytes and plasma cells was identified. Immunohistochemical study showed that the tumor cells in all cases were positive for vimentin and CD68. They were negative for S100 protein, cytokeratin, CD34, CD31, smooth muscle actin, CD35, CD21 and CD30. Two cases also expressed CD99 and one of them was positive for desmin and epithelial membrane antigen. Fluorescence in-situ hybridization was positive for EWSR1 gene.

CONCLUSIONSSolid type represents a variant of angiomatoid fibrous histocytoma and is considered as tumor of borderline malignant potential. Definitive diagnosis requires thorough histologic examination and clinical correlation. Immunohistochemistry and EWSR1 gene study are helpful in further delineation and differential diagnosis. Complete resection or wide local excision with post-operative follow up is the main modality of treatment.