Pleomorphic adenoma (PA), the most prevalent salivary gland tumor, exhibits a diverse histological spectrum characterized by epithelial, myoepithelial, and mesenchymal patterns, and secretory products. However, a subset of PAs presents microscopic features suggestive of malignancy, leading to challenging and potentially significant diagnostic pitfalls. A comprehensive retrospective analysis was conducted on the Salivary Gland Tumor Registry, compiled by the authors. A total of 104 cases diagnosed between 1960 and 2023 were retrieved. Clinical findings, pathological features, and molecular genetic results were analyzed. In the study of 104 PA cases, 23 (22.1%) presented features suggestive of pseudoinvasion, with satellite nodules being the most common (43.5%) along with capsular penetration, irregular growth, pseudopodia, lipomatous changes, and vascular permeation. Features of pseudomalignant cytomorphology were found in 97 cases (93.3%), characterized by increased cellularity, cellular atypia, heightened proliferative activity, oncocytic metaplasia, and necrosis. Additionally, 30 cases (28.8%) displayed features resembling other defined malignant salivary gland tumors, particularly myoepithelial carcinoma, adenoid cystic carcinoma, and polymorphous adenocarcinoma. Despite PA's generally straightforward diagnosis, cases with these features may be mistakenly interpreted as malignant tumors. The shared morphocytological features underscore the complexity of an accurate diagnosis, emphasizing the need for meticulous examination and a comprehensive assessment, incorporating morphological, molecular, and immunohistochemical analyses to differentiate between benign and malignant salivary gland tumors, in selected cases.

• Keywords
• Atypical, Mimic of malignancy, Pitfall, Pleomorphic adenoma, Salivary gland neoplasms,
• Publication type
• Journal Article MeSH

INTRODUCTION: A vast increase in knowledge of numerous aspects of malignant salivary gland tumours has emerged during the last decade and, for several reasons, this has not been the case in benign epithelial salivary gland tumours. We have performed a literature review to investigate whether an accurate histological diagnosis of the 11 different types of benign epithelial salivary gland tumours is correlated to any differences in their clinical behaviour. METHODS: A search was performed for histological classifications, recurrence rates and risks for malignant transformation, treatment modalities, and prognosis of these tumours. The search was performed primarily through PubMed, Google Scholar, and all versions of WHO classifications since 1972, as well as numerous textbooks on salivary gland tumours/head and neck/pathology/oncology. A large number of archival salivary tumours were also reviewed histologically. RESULTS: Pleomorphic adenomas carry a considerable risk (5-15%) for malignant transformation but, albeit to a much lesser degree, so do basal cell adenomas and Warthin tumours, while the other eight types virtually never develop into malignancy. Pleomorphic adenoma has a rather high risk for recurrence while recurrence occurs only occasionally in sialadenoma papilliferum, oncocytoma, canalicular adenoma, myoepithelioma and the membranous type of basal cell adenoma. Papillomas, lymphadenoma, sebaceous adenoma, cystadenoma, basal cell adenoma (solid, trabecular and tubular subtypes) very rarely, if ever, recur. CONCLUSIONS: A correct histopathological diagnosis of these tumours is necessary due to (1) preventing confusion with malignant salivary gland tumours; (2) only one (pleomorphic adenoma) has a considerable risk for malignant transformation, but all four histological types of basal cell adenoma can occasionally develop into malignancy, as does Warthin tumour; (3) sialadenoma papilliferum, oncocytoma, canalicular adenoma, myoepithelioma and Warthin tumour only occasionally recur; while (4) intraductal and inverted papilloma, lymphadenoma, sebaceous adenoma, cystadenoma, basal cell adenoma (apart from the membranous type) virtually never recur. No biomarker was found to be relevant for predicting recurrence or potential malignant development. Guidelines for appropriate treatment strategies are given.

• Keywords
• Benign salivary gland tumours, Biomarkers, Malignant transformation, PubMed, Recurrence, Salivary gland neoplasms, Treatment modalities,
• MeSH
• Adenoma classification   diagnostic imaging   MeSH
• Adult MeSH
• Middle Aged MeSH
• Humans MeSH
• Adenoma, Pleomorphic classification   diagnostic imaging   MeSH
• Aged, 80 and over MeSH
• Aged MeSH
• Salivary Glands cytology   diagnostic imaging   MeSH
• Check Tag
• Adult MeSH
• Middle Aged MeSH
• Humans MeSH
• Male MeSH
• Aged, 80 and over MeSH
• Aged MeSH
• Female MeSH
• Publication type
• Journal Article MeSH
• Review MeSH