Abstract
BackgroundEpithelioid cell histiocytoma (ECH), which is also known as epithelioid benign fibrous histiocytoma, has been classified as a rare variant of fibrous histiocytoma (FH). However, the recent detection of ALK protein expression and/or ALK gene rearrangement in ECH suggests that it might be biologically different from conventional FH.Case presentationA 27-year-old male presented with nodule on his left foot, which had been present for 5 years. A macroscopic examination revealed an exophytic, hyperkeratotic nodule on the dorsum of the left foot. Tumorectomy was performed, and a microscopic examination showed a subepidermal lesion composed of sheets of tumor cells with oval to round nuclei and ill-defined eosinophilic cytoplasm. The tumor cells were diffusely positive for factor XIIIa and ALK, but were negative for AE1/AE3 keratin, alpha-smooth muscle actin, CD30, CD34, CD68, PU.1, melan A, MITF, and S-100 protein. ALK immunostaining showed a diffuse cytoplasmic staining pattern. ALK fluorescence in situ hybridization demonstrated break-apart signals, which was suggestive of ALK rearrangement. A 5′-rapid amplification of cDNA ends assay detected SQSTM1-ALK fusion, in which exon 5 of the SQSTM1 gene was fused to exon 20 of the ALK gene. The patient was free from recurrence and distant metastasis at the 1-year of follow-up.ConclusionWe were able to demonstrate the SQSTM1-ALK fusion gene in ECH. Practically, detecting immunopositivity for ALK and appropriate cell-lineage markers are the key to diagnosing ECH.
Highlights
Epithelioid cell histiocytoma (ECH), which is known as epithelioid benign fibrous histiocytoma, has been classified as a rare variant of fibrous histiocytoma (FH)
Epithelioid cell histiocytoma (ECH), which is known as epithelioid benign fibrous histiocytoma, is generally considered to be an epithelioid variant of fibrous histiocytoma (FH) of the skin [1,2,3,4]
A microscopic examination of hematoxylin and eosin (H&E)-stained slides performed at low magnification showed a nodular, dermal-based tumor surrounded by an epidermal collarette (Fig. 2)
Summary
We were able to demonstrate the SQSTM1-ALK fusion gene in ECH. Practically, detecting immunopositivity for ALK and appropriate cell-lineage markers are the key to diagnosing ECH.
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