Sebaceous Adenocarcinoma in Parotid Gland of a 65-Year-Old

Sebaceous adenocarcinoma of the parotid gland is a rare, malignant epithelial neoplasm with focal areas of sebaceous differentiation. A literature search revealed only 34 cases as of December 2020. Our case brings this total to 35. It is characterized as a partially encapsulated neoplasm with predominant areas of basaloid or squamous cells, and variable degrees of sebaceous differentiation. The sebocytes display an immunohistochemical staining pattern of EMA (cytoplasmic vesicles), CD15, lactoferrin, GCDFP-2, and androgen receptor positivity in the sebocytes. Bimodal peaks occur in the third and seventh decades of life. We present a case of sebaceous adenocarcinoma in a 65-year-old male who initially presented in the emergency department with hypertensive urgency and vertigo. MRI and CT scans showed a heterogeneous mass with a solid component and cystic areas, including calcifications that measured approximately 2.7 x 2.1 x 4.1 cm, predominantly in the deep part of the left parotid gland and extending upward to the adjacent sternocleidomastoid muscle and possibly infiltrating or abutting the muscle. Further questioning of the patient revealed a seven month history of a painless, slow-growing mass and increased sensation of fullness on the left side of his neck. Patient underwent a left total parotidectomy with flap reconstruction and left neck dissection, revealing a 6.0 x 4.4 x 2.2 cm left parotid gland with a 2.4 x 2.2 x 1.6 cm, well-circumscribed, multiloculated cystic mass that released red-brown serous fluid and thick yellow material and appeared to abut multiple resection margins. Microscopic examination showed nests of basaloid cells at the periphery and areas of distinct sebaceous differentiation, separated by bands of extensive hyalinization. The tumor also displayed an average of 2 mitotic figures per 10 high power fields, and less nuclear atypia and less invasiveness into the surrounding glandular tissue than what has been described in sebaceous adenocarcinomas. This is an unusual case because of the rarity of the tumor as well as the lack of nuclear atypia and invasiveness compared to what is described of sebaceous adenocarcinoma in the literature.