Pleomorphic Adenomas of the Salivary Glands: Retrospective Multicentric Study of 130 Cases with Emphasis on Histopathological Features

Pleomorphic adenoma (PA) is the most frequent benign epithelial lesion of salivary gland origin, showing great histopathological diversity. The aim of this study was to perform a retrospective analysis, with emphasis on histopathologic features of PA of salivary glands. Clinical and histopathologic characteristics of 130 cases of minor and major salivary glands PAs from three Brazilian reference centers were studied. Higher frequency of PAs was observed in female (55.4 %) subjects, with mean age of 49.7 years. The most common affected site was palate (64.5 %) for the PAs of minor salivary glands and parotid for cases affecting major glands (86.2 %). Microscopically, most cases were classified as classic PAs (50 %). Incomplete capsule was observed in 36.2 % of the cases, while 47.2 % showed capsular infiltration. Rounded (66.9 %), angular (49.2 %), oval (46.2 %) and plasmacytoid (39.2 %) cells were widely observed, as well as fibrous (73.8 %) and myxoid (69.2 %) stroma, squamous metaplasia (25.4 %) and cystic degeneration (43.1 %). Crystalloids (3.1 %), increased mitotic activity (5.4 %) and vascular invasion (2.3 %) were rarely observed. PAs arising in minor salivary glands were associated with incomplete capsules, spindle, oval, angular, plasmacytoid and pleomorphic cells, fibrous and hyaline stroma, cystic degeneration, squamous metaplasia and pleomorphism (p < 0.05). No association between capsular features and histological subtype was noted (p ≥ 0.05). These results confirm the findings of previous studies regarding major clinicopathological features of pleomorphic adenomas; and highlighted some important morphologic characteristics like the capsule, vascular invasion, pleomorphism and increased mitotic activity, which can reflect the biological behavior of these tumors.