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Case Reports

Abstract

Anaplastic lymphoma kinase (ALK) gene fusions occur in several cutaneous neoplasms including epithelioid fibrous histiocytoma (FH) and likely related non-neural granular cell tumor, rare cases of primary inflammatory myofibroblastic tumor, and recently described superficial ALK-rearranged myxoid spindle cell neoplasm (SAMS). The latest studies show some ALK-rearranged tumors have hybrid features of SAMS and epithelioid FH, suggesting the two entities may also be morphologically and genetically related. Here, we report one such case in a 45-year-old woman who presented with a right flank nodule clinically suspicious for an angioma, irritated nevus, or dermatofibroma. Sections demonstrated a dermal-based infiltrative biphasic neoplasm composed of plump spindled cell fascicles alternating with distinct perineurioma-like whorls composed of slender fibroblasts set in a vascular myxoid stroma. Both components also showed epithelioid cells with amphiphilic cytoplasm and intranuclear cytoplasmic inclusions like those seen in classic epithelioid FH. By immunohistochemistry, the tumor cells expressed CD34, S100 and Factor XIIIa. Notably, the immunostaining pattern was also biphasic, with the plump spindled and epithelioid FH-like cells expressing Factor XIIIa, while the slender fibroblasts in the myxoid nodules were positive for CD34 and almost completely negative for Factor XIIIa. Both components showed strong diffuse expression of ALK (D5F3). The tumor cells were negative for AE1/3, SOX10, NKI-C3 and neurofilament. These findings further substantiate the hypothesis that SAMS and epithelioid FH may represent a morphologic and genetic spectrum. The differential diagnosis, clinical follow up, and the molecular genetic findings will be discussed.