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Case Reports

Abstract

A 16-year-old female with no significant personal medical history and a family history of melanoma in a first-degree relative presented to dermatology clinic for a left antihelix lesion present for two months. Physical exam revealed a 5 mm light-pink hyperkeratotic papule with punctate vessels. Clinically, the lesion was favored to represent a verruca vulgaris; other benign entities—including prurigo nodule and irritated intradermal nevus—were also considered. A shave biopsy showed a compound melanocytic proliferation with Spitzoid features. Additionally, there were concerning features, including partial epidermal consumption, scattered mitoses with deep mitoses, and an elevated Ki67 proliferation index. Gradient expression of HMB45, p16 retention, and negative PRAME argued against malignant melanoma. While an atypical Spitz tumor (AST) was favored, the specimen was forwarded to an outside institution for expert consultation and molecular studies. Next generation sequencing demonstrated the following pertinent alterations: TPM3::NTRK1 fusion, chromosome 1p distal loss, chromosome 1q distal gain, and a single-copy loss of CDKN2A. The finding of a NTRK1 fusion and negative immunohistochemical expression of BRAFVE1 supports the morphologic impression of a Spitz lesion. Additional copy number changes involving chromosome 1q and 1p without molecular hallmarks of malignancy corroborated the diagnosis of  AST. Staged re-excision with 2–5 mm margins—without sentinel lymph node biopsy—was recommended and performed and there was no evidence of residual AST. This case demonstrates the utility of molecular studies in the diagnosis of an AST, particularly in the clinical context of a young patient with a lesion at a sensitive site.