Microsecretory adenocarcinoma of the external ear canal

Microsecretory adenocarcinoma (MSA) is a recently described salivary gland tumor characterized by unique histomorphologic and immunohistochemical features as well as recurrent MEF2C::SS18 gene fusion. Since 2019, 24 cases have been reported in the literature, primarily arising in the oral cavity, with a single reported case arising in the parotid gland. Here, we present a case of MSA that arose in the external ear canal in an 89‐year‐old woman and was discovered during management of vertigo symptoms. Excisional biopsy of the lesion showed multiple fragments of squamous epithelium with hyperplastic changes and a distinct subepithelial infiltrating neoplasm composed of bland cells forming tubules and cords. Neoplastic cells expressed keratin, S100 protein, p63, and TLE1 and did not express p40, mammaglobin, pan‐TRK, synaptophysin, or chromogranin by immunohistochemistry. SS18 gene rearrangement was shown with break‐apart fluorescent in situ hybridization. Overall, the histomorphologic, immunohistochemical, and cytogenetic findings confirm a diagnosis of MSA arising in a unique extraoral location.