Track

Case Reports

Abstract

Kinase positive soft tissue tumors are an emerging entity of mesenchymal tumors with a wide morphologic spectrum with the potential for local recurrence but rare metastasis. The CARS::ALK fusion has been reported in inflammatory myofibroblastic tumors (IMT), epithelioid fibrous histiocytoma, and a low-grade myofibroblastic sarcoma. We describe two unique cases with CARS::ALK fusions which possess previously unreported histologic features and immunohistochemical profiles. The first case is of a 42-year-old female with a history of thyroid cancer who presented with a 2-month history of two painful papules on the left frontal scalp and forehead. Biopsies revealed a variably cellular proliferation of plump spindle cells with mild atypia and low mitotic activity. The tumor had floret-like giant cells and involved the deep reticular dermis and subcutis similar to a lipofibromatosis-like neural tumor. The lesion was positive for CD34, ALK, and CD163 (partial) and negative for S100 and SOX10. The second case is of a 12-year-old male who presented with a 1.4 cm firm subcutaneous nodule on the right shin. Histology showed spindle cells arranged in whorled fascicles in a variably myxoid and keloidal stroma. Nuclear atypia was mild and mitotic activity was not noted. The tumor was positive for ALK, CD10, SMA (partial), and negative for desmin, CD34, S100, and SOX10. The characteristic inflammatory background of IMT was absent. Next generation sequencing demonstrated a CARS::ALK fusion in both cases. We present these two cases to expand the spectrum of morphologic and immunohistochemical features in CARS::ALK rearranged cutaneous spindle cell neoplasms.