Microsecretory adenocarcinoma of the skin, a novel type of sweat gland carcinoma: Report of three additional cases.

Microsecretory adenocarcinoma (MSA) is a newly described salivary gland tumor harboring a characteristic balanced chromosomal translocation resulting in MEF2C::SS18 gene fusion. Six primary cutaneous MSA cases have been recently described. We report three additional cases confirming the relevance of this recently identified entity of primary cutaneous adnexal tumor. Three patients aged 53-, 64- and 78-year-old were retrospectively diagnosed with MSA of the skin (MSAS) as consultation cases of the CARADERM (CAncers RAres DERMatologiques) national network. The clinical presentation was an indolent nodule on the upper extremities. There was no history of salivary gland tumor. Histopathologically, the tumors presented as dermal nodular proliferation with slightly infiltrative borders, composed of cribriform and microcystic structures with abundant myxoid intraluminal secretion embedded in a fibromyxoid stroma. They diffusely expressed cytokeratin 8 and SOX10, focally p63 and heterogeneously smooth muscle actin. All tumors harbored the MEF2C::SS18 gene fusion. A complete surgical excision was performed. No local recurrence or distant metastases were observed so far (follow-up: 17, 38, and 45 months). MSAS is the cutaneous homologue of MSA of the salivary gland, a low-grade adnexal neoplasm whose prognosis seems to be excellent once the complete removal of the tumor is assured.