Aim: Report of two cases of benign skin tumors of different histogenesis with anaplastic lymphoma kinase (ALK) gene rearrangement. Introduction: ALK gene mutation or rearrangement positive tumors (ALKomas) are heterogeneous group in which such genetic finding has diagnostic or predictive value. ALK gene fusions are associated with tumorigenesis of some cutaneous tumors, e.g. plexiform Spitz nevus (PSN) and epithelioid fibrous histiocytoma (EFH). Cases reports: Histological, immunohistochemical (IHC) and genetic characteristics were analyzed in two skin tumors with ALK gene rearrangement proved by fluorescent in situ hybridization (FISH). First case is PSN localized on face in a 8-year-old boy. Tumor was consisted of spindle cells arranged in plexiform growth pattern throughout epidermis and dermis, with following IHC characteristics: HMB45  focally, p16 , Ki67  in 1% of cells. Deletion of CDKN2A gene was not detected in significant number, while ALK gene rearrangement was positive in 37/50 (74,2%) of cells. Second case is EFH localized on shoulder in a 16-year-old girl. This dermal based tumor was consisted of tightly packed large epithelioid cells, which were CD68 , p16 , S100-, HMB45-, SOX10-, CD1a-, Ki67 (<5% of cells). ALK gene rearrangement was positive in 24/100 (24%) of cells, and focal chromosome 2 polysomy was noted. Neither mitoses nor necrosis were present in any of presented cases. Conclusion: Skin ALKomas are tumors with heterogeneous histological and immunohistochemical characteristics, and also with variable extent of ALK rearrangement.

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