Histopathological features of polymorphous adenocarcinoma: A case series.

Polymorphous adenocarcinoma (PAC) is a malignant neoplasm of the salivary gland with a low incidence worldwide, characterized by diverse morphological features. This study aimed to present a large and well-documented case series from a single Brazilian center. We analyzed demographic data, clinical presentations, histopathological features, and immunohistochemical characteristics of 26 cases of PAC. Most patients were women (n = 21), with a mean age of 58 years (range = 36 to 84 years). The typical clinical presentation was a fibrous/fibroelastic and firm nodular lesion, with an average diameter of 2 cm, most found on the palate (n = 15). The alveolar ridge, buccal mucous, and superior lip were also affected. Histologically, various patterns were observed, including tubular, solid, cribriform, papillary, and cystic. Glomeruloid slit-like structures (n = 11), clear cells (n = 13), and mucous cells (n = 8) were also identified. Surface papillary epithelial hyperplasia was observed in four cases, and the presence of myxoid and collagenous areas in the stroma in nine. Fusiform areas were noted in 2 cases and areas of squamous differentiation in one. A clear cell predominance was observed in 2 cases. Neural invasion was present in eight cases. All cases were positive for S-100 and Cytokeratin 7 (CK7), and negative for p-40. The Ki-67 index was low, with a mean of 2.5%. In this case series, PAC primarily affected minor salivary glands and exhibited some uncommon microscopic features. Oral pathologists should be aware of these findings to prevent misdiagnosis. [ABSTRACT FROM AUTHOR]