Key result
A SQSTM1-ALK gene fusion was identified in a 27-year-old male with epithelioid cell histiocytoma, demonstrating that this fusion can occur in this rare tumor variant.
Case Report (n=1)
No
This case report demonstrates the presence of the SQSTM1-ALK fusion gene in epithelioid cell histiocytoma, supporting its biological distinction from conventional fibrous histiocytoma.
Does not change diagnostic standards; extends the molecular spectrum of ALK fusions in rare histiocytomas.
BACKGROUND: Epithelioid 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 PRESENTATION: A 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. CONCLUSION: 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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Nakayama et al. (2018) conducted a case report in Epithelioid cell histiocytoma (n=1). SQSTM1-ALK fusion was evaluated on Detection of SQSTM1-ALK fusion. A SQSTM1-ALK gene fusion was identified in a 27-year-old male with epithelioid cell histiocytoma, demonstrating that this fusion can occur in this rare tumor variant.
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