Myoepithelioma of the parotid gland with extensive adipocytic metaplasia: Report of a case with intriguing aspects on fine needle aspiration and p63 immunohistochemical expression

Myoepithelioma is a rare and usually benign salivary gland tumor derived from myoepithelial cells. Variability in cellular morphology and stromal composition leads to diagnostic pitfalls on fine-needle aspiration cytology; therefore, histology and immunohistochemistry are often required for definitive diagnosis. We describe a case of parotid gland myoepithelioma in a 76-year-old woman, which was discovered incidentally on cerebral magnetic resonance imaging. Fine-needle aspiration sampled cohesive aggregates of spindle-shaped cells embedded in a fibrillary matrix as well as abundant mature adipocytes, initially considered as part of normal salivary gland parenchyma. Histology of the resected specimen showed bundles of spindle-shaped cells embedded in loose connective tissue, admixed with numerous intralesional adipocytes. Immunohistochemical studies revealed a diffuse expression of p63 by this adipocytic population, an observation clearly indicating that myoepithelial cells can trans-differentiate and acquire the morphology of mature adipocytes. Knowledge of this phenomenon can be helpful in the work-up of salivary gland lesions. Diagn. Cytopathol. 2016;44:1090-1093. © 2016 Wiley Periodicals, Inc.