Abstract:

A 55-year-old man presented with a growing, painful soft tissue mass of the dorsal left foot. Following surgical excision, gross examination showed multiple fragments of tan and smooth soft tissue measuring 2.9 cm in aggregate. Microscopic examination demonstrated a well-circumscribed, nonencapsulated tumor within the dermis. The tumor was predominantly cystic with much of the cystic growth lined by a thin, 1-to-3 cell thick layer. Focal solid growth was also present with scattered small duct formation present. The cells were small and uniform cuboidal cells with abundant eosinophilic cytoplasm. No significant cytologic atypia, mitotic figures, necrosis, or invasion was seen. The cells were immunoreactive toward antibodies for SOX10, p63 and NUT, with focal expression of EMA in the areas of duct formation. CEA was negative. The proliferation index by Ki-67 staining was less than 10% and p16 showed a patchy, wild-type expression pattern, supporting the morphologic impression of a benign poroid hidradenoma. Poroid hidradenoma is a rare benign tumor with eccrine sweat gland differentiation. In recent literature, this entity and the other cutaneous poroid neoplasms (poroma, porocarcinoma) have been reported to harbor NUTM1 and YAP1 fusions with various fusion partners. Nuclear NUT expression by immunohistochemistry is highly sensitive (87%) and specific (100%) in detecting NUTM1 fusions, regardless of the fusion partner. While NUT expression has been reported in a high percentage of poroid hidradenomas, the current data is still conflicted on whether NUTM1 fusions are more common in benign or malignant cutaneous poroid lesions. The current case is notable for the prevailing cystic component, which has not been reported in a NUT-positive poroid hidradenoma to the authors’ knowledge.

Financial Disclosure:
No current or relevant financial relationships exist.

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Tappy Gish, MD