Salivary Duct Carcinoma arising from pre-existing Epithelial-Myoepithelial Carcinoma of the parotid gland: Another rare example with Cytological Correlation

An extremely exceptional case of salivary duct carcinoma (SDC) arising from pre-existing epithelial-myoepithelial carcinoma (EMC) of the parotid gland is herein described. The patient was a 50-year-old Japanese female, who presented with an asymptomatic mass of the right parotid gland that had been present for approximately 7 years. A superficial lobectomy of the parotid gland was performed and there have been no symptoms of recurrence or distant metastasis during over 10-year follow-up period. Histologically, the tumor was composed of an EMC component having double-layered ducts and invasive nests of myoepithelial clear cells with an SDC component intermingled throughout the lesion, which consisted of eosinophilic pleomorphic cells. Nests of the SDC component were occasionally accompanied by small luminal structures and minimally focalized comedo necrosis, and were immunoreactive for androgen receptor and GCDFP15. Fine needle aspiration cytology showed moderate cellularity, a few three-dimensional or sheet-like clusters, and single dispersed cells with abundant granular cytoplasm in the background. Furthermore, hyperchromatic small or flattened cells were identified attaching to the periphery of the clusters in retrospective observation. Metachromasia was also seen in May-Grunwald Giemsa stain. Keywords: Salivary duct carcinoma; Epithelial-myoepithelial carcinoma; Parotid gland; Dedifferentiation; High-grade transformation; Fine needle aspiration cytology