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Case Reports

Abstract

Anaplastic lymphoma kinase (ALK) is a receptor tyrosine kinase whose gene fusions can drive development of lymphomas, spitzoid melanocytic tumors, inflammatory myofibroblastic tumors, epithelioid fibrous histiocytomas, and more recently, superficial ALK-rearranged myxoid spindle cell neoplasms (SAMS). First coined in 2021, this soft tissue neoplasm results from fusion of ALK with proteins including filamin A, myosin heavy chain 10, homeobox containing 1; pleckstrin homology, MyTH4 and FERM domain containing H2; EMAP like 4; and fragile X messenger ribonucleoprotein 1. To date, 22 cases of SAMS exist in the literature. This neoplasm arises in children and adults and presents as a papule or nodule on the back or lower extremities. The clinical differential may include basal cell carcinoma, nevus, cyst, or dermatofibrosarcoma protuberans. Microscopically, SAMS appears as clusters of corded spindled or epithelioid cells embedded in a myxoid stroma and displays ALK, CD34, and S100 positivity. We present a case of a 63-year-old woman with a pigmented papulonodule on the left lateral leg clinically suspected to be a dermatofibroma. Punch biopsy demonstrated an S100, CD34, and ALK positive bland intradermal spindle cell proliferation. PDGF-beta rearrangement, as well as MiTF, NKI/C3, and NTRK were negative. The patient elected conservative excision of the lesion.  The constellation of findings supported the diagnosis of SAMS.  Future studies may characterize the long-term behavior of SAMS and correlate clinical outcomes with ALK fusions associated with this rare tumor. This is important as local recurrence, metastasis, and death have been reported with this tumor.