Microsecretory adenocarcinoma: Cutaneous counterpart of a newly described salivary gland tumor with recurrent MEF2C::SS18 fusion.

Microsecretory adenocarcinoma (MSA) is a distinctive low-grade salivary gland tumor with a novel MEF2C::SS18 fusion. Although MSA most commonly occurs in the oral cavity, cases of MSA involving skin have been described recently. Histopathologically, MSA is characterized by microcystic tubules with basophilic luminal secretions, a fibromyxoid stroma and cells with eosinophilic or clear cytoplasm, and a unique immunohistochemical profile (S100+, SOX10+, p63+, and p40-). Cutaneous MSA may rarely demonstrate high-grade features. Follow-up studies have shown MSA to be an indolent tumor, without local recurrence or metastasis after complete surgical excision in the vast majority of cases. It is important to recognize the histopathological features of this unique tumor with a novel MEF2C::SS18 fusion that may occur in skin and to utilize appropriate molecular studies for accurate diagnosis.