Epithelioid Fibrous Histiocytoma With Chondroblastoma-Like Features: A Report of a Rare Entity and Discussion of Related Diagnostic Challenges

Abstract

Epithelioid fibrous histiocytoma (EFH) is an uncommon benign skin lesion. It is distinct from FH by virtue of its recurrent anaplastic lymphoma kinase (ALK) gene rearrangements and immunohistochemical expression of ALK protein. It often poses a challenge in interpretation. Clinically, it is characterized by a fleshcolored papule/nodule on an extremity of a young to middle-aged individual. Microscopically, it is represented by a circumscribed dermal papule/nodule composed of sheets of plump epithelioid cells, forming whorled aggregates around numerous intralesional vessels. Immunohistochemistry, notably ALK positivity and relevant negative stains, serves to distinguish EFH from its morphological mimics. Rare examples of chondroblastoma-like EFH and EFH with osseous metaplasia are recorded in the literature. Our case is of a 58-year-old man who attended an oculoplastic surgeon because of an exophytic cutaneous nodule on the right upper eyelid. The lesion was excised. Microscopically, it displayed morphological and immunohistochemical features of EFH. Of interest, discrete foci of chondro-osseous change, including chondroblastoma-like pericellular calcification, osteoid formation, and osteoclast-like giant cells, were noted throughout the lesion. A diagnosis of EFH with chondroblastomalike features was made. Of interest, the changes observed in this EFH serve to link the previously reported examples of pure chondroblastoma-like EFH and EFH with osseous metaplasia. This morphological variant of EFH adds to the existing diagnostic challenge presented by these lesions, particularly in the distinction from other calcifying tumors of the skin.

A Novel Fusion Partner, SP100, Drives Nuclear Dot Localization of ALK in Epithelioid Fibrous Histiocytoma

“…2 In recent years, new morphologic variants have been described, including those which show a spindled and chondroblastoma-like morphology. 3–8…”

“…2 In recent years, new morphologic variants have been described, including those which show a spindled and chondroblastoma-like morphology. [3][4][5][6][7][8] The defining molecular feature of EFH is the presence of anaplastic lymphoma kinase (ALK) gene fusions 9,10 which lead to hyperactive ALK signaling. At least 14 different ALK fusion partners have been described to date (summarized in Table 1).…”