Oncocytic low-grade myoepithelial carcinoma ex pleomorphic adenoma – A rare case illustrating key learning points

• Published in: Annals of diagnostic pathology 2022-10, Vol.60, p.152011-152011, Article 152011
• Main Authors: Tay, Wan Jing, Tan, Gideon Ze Lin, Wu, Bingcheng, Petersson, Fredrik
• Format: Article
• Language: English
• Subjects: Carcinoma; Carcinoma ex pleomorphic adenoma; Fine needle aspiration cytology; Immunohistochemistry; Myoepithelial carcinoma; Oncocytic; Pleomorphic adenoma
• ISSN: 1092-9134; 1532-8198
• DOI: 10.1016/j.anndiagpath.2022.152011

Oncocytic myoepithelial carcinoma ex pleomorphic adenoma neoplastic is a rare neoplastic event and may not display overt malignant radiological features. Using routine histopathology and immunohistochemistry, we characterize a case of low-grade oncocytic carcinoma ex pleomorphic adenoma. The tumor arose in the left parotid gland in a 59 year old female. Computed tomography (CT) imaging demonstrated a well-defined, lobulated, enhancing lesion with relative central stellate hypoenhancement. Histologically, the tumor displayed a multi-nodular, non-destructive, invasive pattern, low mitotic activity (one mitotic figure per 10 high power fields) and a small remnant focus of pleomorphic adenoma. The neoplastic cells showed significant expression of cytokeratin 5/6, S-100 protein, smooth muscle actin and p63. Low-grade oncocytic carcinoma ex pleomorphic adenoma is a challenging histopathological diagnosis which can be established with use of immunohistochemistry, generous tumor sampling and recognition of the multi-nodular, non-destructive, pattern of invasion. In the absence of clear-cut tumor encroachment into external structures, its malignant nature may not be easily identified on pre-operative imaging. •Recognize the multinodular, low-grade pattern of invasion of myoepithelial carcinoma.•Myoepithelial neoplasms may rarely demonstrate oncocytic differentiation.•Thorough sampling and comprehensive immunohistochemical study are essential.•Obviously malignant features be absent in pre-operative imaging.