De Novo Polymorphous Adenocarcinoma of Parotid Gland – A Rare Case Report

Polymorphous adenocarcinoma (PAC), previously termed as polymorphous low-grade adenocarcinoma, is an indolent malignant neoplasm of the minor salivary glands and is most commonly located in the palate, but is rarely described in major salivary glands like the parotid gland. The terminology has been changed in the World Health Organization (WHO) classification of salivary gland tumors (2017) due to the aggressive behavior of a few cases. Polymorphorphous adenocarcinoma in the parotid gland can arise either de novo or as neoplasms developing in a pre-existent pleomorphic adenoma, as carcinoma ex pleomorphic adenoma. De novo PAC arising in the parotid gland is very rare, and only a few case reports are available in the literature. We report here a rare case of de novo PAC of the left parotid gland in a 70-year-old female patient. It may cause diagnostic difficulty on preoperative fine needle aspiration cytology. Histopathological examination is confirmatory because of its diverse morphology; IHC may help in definitive diagnosis.