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Case Reports

Abstract

In the 5th edition of the WHO Classification of Skin Tumors, NUT adnexal carcinoma (NAC) was introduced as a new provisional entity with a NUT gene rearrangement. In contrast to the classic midline NUT carcinoma, the histopathologic appearance of NAC resembles a sweat gland carcinoma, not squamous cell carcinoma. Furthermore, the gene fusion partners of NAC differ from poroid neoplasm. Given the rarity of NAC and limited knowledge of the spectrum of clinical behavior and pathologic features, we present a patient who developed a pulmonary metastasis 11 years after the primary presentation with a positive sentinel lymph node.

A 35-year-old woman presented for evaluation of a 2.5 by 2.5 cm firm, brown, fungating right thigh mass. Biopsy and histopathologic evaluation revealed an ulcerated sweat gland carcinoma. The tumor was composed of both epithelial and myopithelial elements but displayed infiltrative growth and atypia. The tumor was excised with negative margins. A right inguinal sentinel lymph node biopsy revealed metastatic carcinoma. A completion lymphadenectomy was negative for tumor. No tumor recurrence was noted until 11 years after her primary tumor, when 2 small, slowly growing pulmonary nodules were identified on surveillance CT. The patient underwent a wedge resection, which revealed metastatic sweat gland carcinoma. Molecular analysis revealed a BRD3::NUTM1 gene fusion, which now permitted the subclassification of the sweat gland carcinoma as NUT adnexal carcinoma. This case illustrates the value of molecular testing for the classification of sweat gland carcinomas and the need for long term follow-up to assess their biologic potential