title: A rare case of cutaneous oncocytic hidradenoma.
abstract: Oncocytes are epithelial cells characterized by their abundant eosinophilic and finely granular cytoplasm. Their histologic appearance is due to excessive amounts of cytoplasmic mitochondria. Oncocytes generally occur in the setting of benign neoplasms. Oncocytomas, or tumors composed primarily of oncocytes, are typically found in the kidneys. Other common sites include the salivary, thyroid, and parathyroid glands. Oncocytic metaplasia has only been rarely reported in various cutaneous neoplasms. We report a case of an elderly male presenting with a 5 mm erythematous papule on his left scalp, who underwent a shave biopsy showing a nodular, dermal-based adnexal tumor with prominent ductal differentiation, composed of multiple small, well-formed lumina surrounded by enlarged and bland-appearing epithelioid cells. Cytokeratin 7 (CK7), epithelial membrane antigen (EMA) and monoclonal carcinoembryonic antigen (mCEA) immunohistochemical stains were positive, consistent with adnexal differentiation. Phosphotungstic acid-hematoxylin (PTAH) and Luxol fast blue (LFB) stains highlighted the cytoplasmic granules, consistent with mitochondria. The overall findings were consistent with an oncocytic nodular hidradenoma. Oncocytic hidradenoma is a very rare entity, with only 1 previously reported case in the literature.
authors.affiliation: School of Medicine, University of Illinois at Chicago College of Medicine, Chicago, Illinois.
authors.forename: Shivani P
authors.identifier: http://orcid.org/0000-0003-3295-8021
authors.initials: SP
authors.lastname: Reddy
authors.affiliation: Departments of Dermatology and Pathology, Kaiser Permanente Los Angeles Medical Center, Los Angeles, California.
authors.forename: Kim
authors.initials: K
authors.lastname: Chong
authors.affiliation: Departments of Dermatology and Pathology, Kaiser Permanente Los Angeles Medical Center, Los Angeles, California.
authors.forename: David S
authors.identifier: http://orcid.org/0000-0001-8875-0858
authors.initials: DS
authors.lastname: Cassarino
mesh_terms: D018250:Acrospiroma / Q000473:pathology*; D000368:Aged; D014408:Biomarkers, Tumor / Q000032:analysis; D002280:Basal Cell Carcinoma / Q000473:pathology; D006801:Humans; D007150:Immunohistochemistry; D008297:Male; D016609:Neoplasms, Second Primary / Q000473:pathology; D024862:Oxyphil Cells / Q000473:pathology*; D012878:Skin Neoplasms / Q000473:pathology; D013544:Sweat Gland Neoplasms / Q000473:pathology*
chemical_list: D014408:Biomarkers, Tumor
keywords: hidradenoma; neoplasm; oncocytic