TWO PEAS IN A POD: AN INCIDENTAL FINDING OF SCLEROSING POLYCYSTIC ADENOSIS WITHIN A PLEOMORPHIC ADENOMA

Background: A 55-year-old male patient was urgently referred to the local ear, nose, and throat surgery department with a 1-cm left parotid lump. Initial core biopsy was suggestive of a pleomorphic adenoma with some atypical features. The patient underwent a left parotidectomy.
Case Description: Macroscopic examination showed an intact capsule. Histology showed a small well-defined and encapsulated tumor showing the classical appearance of a pleomorphic adenoma for the most part exhibiting bilayered ducts and mucomyxoid stroma. Toward the periphery, a microcystic pattern was seen with luminal secretory material, prominent apocrine changes, and focal stromal sclerosis with some nuclear and cellular atypia but no evidence of frank malignancy. Immunohistochemistry for p63, SMA, and S100 highlighted the myoepithelial cells and Cam5.2 decorated the luminal cells. Ki67 showed a very low perforation index (<1%). Staining for GCDFP and AR was strong and diffuse within the apocrine and sclerotic areas but lacking within the background pleomorphic adenoma. A final diagnosis of sclerosing polycystic adenosis (SPA) within a pleomorphic adenoma was made. Conclusions: The present case is the first of its kind to show a discrete SPA within a pleomorphic adenoma. SPA is an uncommon recently described salivary gland condition that was initially presumed to be inflammatory in nature and resembles fibrocystic breast disease. It appears to harbor human androgen receptor monoclonality with recent reports suggesting that it should be reclassified as a benign neoplasm. The atypia usually present within an SPA can be easily mistaken for a malignancy, requiring careful histopathologic examination.