Primary Cutaneous NUT Adnexal Carcinoma: A Case Report With Novel Clinical and Pathological Observations

Primary cutaneous NUT adnexal carcinoma is an emerging provisional tumor entity characterized by NUTM1 rearrangement with fusion partners different from poroid neoplasms. These tumors should be distinguished from NUT carcinomas with a histopathologic appearance of poorly differentiated squamous cell carcinoma, which tend to behave more aggressively and demonstrate a widespread anatomic distribution. Since fewer than 20 cases of NUT adnexal carcinoma have been reported in the literature, we report herein another case to enhance our knowledge of the spectrum of clinical and pathologic features associated with this tumor. This case is characterized by an unusual clinical course. The lesion was present and slowly progressed over the course of 13 years prior to biopsy and excision. The tumor was composed of epithelial and myoepithelial elements with a range of features, including ductal, cribriform, and solid, with papillary, secretory, and keratocystic changes. The patient underwent wide local excision and sentinel lymph node biopsy, which revealed metastatic tumor. Molecular testing identified a BRD3-NUTM1 fusion, confirming the diagnosis of NUT adnexal carcinoma. The patient remains disease-free at 1-year follow-up without further therapy.