Epithelioid Fibrous Histiocytoma Involving Deep Dermis and Subcutaneous Adipose Tissue.

Epithelioid fibrous histiocytoma (EFH) commonly occurs in the superficial dermis and is typically surrounded by an epidermal collarette. Deep dermal or subcutaneous involvement in EFH is very uncommon. We present three cases of nodular EFH involving the deep dermis and adipose tissue that showed characteristic cellular features and ALK immunoreactivity typical of EFH. All three cases occurred in adults and were present on the trunk or extremities. The lesions ranged from 0.8 to 2.0 cm in size. Histopathologically, all cases exhibited deep dermal/subcutaneous nodules composed of epithelioid cells with vesicular nuclei and eosinophilic cytoplasm. ALK immunohistochemistry demonstrated either cytoplasmic or cytoplasmic and nuclear labeling. Clinical follow-up period ranged from 4.5 to 23 years and revealed no evidence of recurrence. Our cases further expand the morphological spectrum of EFH and highlight the importance of ALK immunohistochemistry to recognize and differentiate unusual histopathological variants of EFH from its morphological mimics.