ALK1-negative Epithelioid Histiocytoma

Abstract Introduction/Objective We present a case of epithelioid histiocytoma (EH). The epithelioid nature of this lesion imitates the appearance of neoplastic lesions such as melanocytic, dermatofibroma/histiocytoma, non-Langerhans histiocytosis such as reticulohistiocytoma, atypical fibroxanthoma, and rhabdomyosarcoma. Methods/Case Report Due to the unusual morphology and aberrant immunohistochemical staining pattern of this specific case, the sample was analyzed through Next Generation Sequencing (NGS), which showed the presence of a fusion of genes Sequestosome 1 (SQSTM1) and Anaplastic lymphoma kinas (ALK). SQSTM1 gene produces proteins involved in signal transduction pathways as well as autophagy, while ALK mainly serves the role of cellular communication and development. The most well-known ALK fusion partners include SQSTM and Vinculin (VCL), while there are other fusion partners that were more recently discovered such as Dynactin Subunit 1 (DCTN1) and ETS variant transcription factor 6 (ETV6). The spectrum of neoplasms produced through these fusions is wide as seen in lung adenocarcinoma and renal cell carcinoma (EML4-ALK), epithelioid histiocytoma (SQSTM1-ALK and VCL- ALK), pediatric renal cell carcinoma (VCL-ALK) among others. Results (if a Case Study enter NA) NA Conclusion We hope this case is a helpful addition to the literature to further aid diagnoses of future ALK fusion cases.