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,
• MeSH
• Diagnosis, Differential MeSH
• Child MeSH
• Adult MeSH
• Middle Aged MeSH
• Humans MeSH
• Adolescent MeSH
• Young Adult MeSH
• Biomarkers, Tumor analysis   genetics   MeSH
• Salivary Gland Neoplasms * pathology   diagnosis   genetics   MeSH
• Adenoma, Pleomorphic * pathology   genetics   diagnosis   MeSH
• Registries MeSH
• Retrospective Studies MeSH
• Aged, 80 and over MeSH
• Aged MeSH
• Check Tag
• Child MeSH
• Adult MeSH
• Middle Aged MeSH
• Humans MeSH
• Adolescent MeSH
• Young Adult MeSH
• Male MeSH
• Aged, 80 and over MeSH
• Aged MeSH
• Female MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Biomarkers, Tumor MeSH

• This ESMO–EURACAN Clinical Practice Guideline provides key recommendations for managing salivary gland cancer. • The guideline covers clinical and pathological diagnosis, staging and risk assessment, treatment and follow-up. • Treatment algorithms for parotid, submandibular, sublingual and minor salivary gland cancer are provided. • The author group encompasses a multidisciplinary group of experts from different institutions and countries in Europe. • Recommendations are based on available scientific data and the authors’ collective expert opinion.

• Keywords
• ESMO–EURACAN Clinical Practice Guideline, diagnosis, follow-up, salivary gland cancer, treatment,
• MeSH
• Adult MeSH
• Medical Oncology MeSH
• Humans MeSH
• Salivary Gland Neoplasms * diagnosis   therapy   MeSH
• Follow-Up Studies MeSH
• Check Tag
• Adult MeSH
• Humans MeSH
• Publication type
• Journal Article MeSH
• Practice Guideline MeSH
• Geographicals
• Europe MeSH

Diagnosis of salivary gland neoplasms is often challenging due to their high morphological diversity and overlaps. Several recurrent molecular alterations have been described recently, which can serve as powerful diagnostic tools and potential therapeutic targets (e.g. NTRK or RET fusions). However, current sequential molecular testing can be expensive and time consuming. In order to facilitate the diagnosis of salivary gland neoplasms, we designed an all-in-one RNA-based next generation sequencing panel suitable for the detection of mutations, fusions and gene expression levels (including NR4A3) of 27 genes involved in salivary gland neoplasms. Here we present the validation of the "SalvGlandDx" panel on FFPE histological specimen including fine needle aspiration (FNA) cell block material, against the standard methods currently used at our institution. In a second part we describe selected unique cases in which the SalvGlandDx panel allowed proper diagnosis and new insights into special molecular characteristics of selected salivary gland tumors. We characterize a unique salivary gland adenocarcinoma harboring a ZCCHC7-NTRK2 fusion, a highly uncommon spindle cell and pseudoangiomatoid adenoid-cystic carcinoma with MYBL1-NFIB fusion, and a purely oncocytic mucoepidermoid carcinoma, whereas diagnosis could be made by detection of a CRTC3-MAML2 rearrangement on the cell block specimen of the FNA. Further, a rare case of a SS18-ZBTB7A rearranged low-grade adenocarcinoma previously described as potential spectrum of microsecretory adenocarcinoma, is reported. In addition, features of six cases within the spectrum of polymorphous adenocarcinoma / cribriform adenocarcinoma of salivary gland including PRKD1 p.E710D mutations and novel fusions involving PRKAR2A-PRKD1, SNX9-PRKD1 and ATL2-PRKD3, are described.

• Keywords
• Biopsy, Comprehensive, FNA, Molecular, Salivary gland neoplasm, Testing,
• MeSH
• Biopsy MeSH
• Oncogene Proteins, Fusion genetics   metabolism   MeSH
• In Situ Hybridization, Fluorescence MeSH
• Immunohistochemistry methods   MeSH
• Humans MeSH
• Mutation MeSH
• Biomarkers, Tumor * MeSH
• Cell Line, Tumor MeSH
• Salivary Gland Neoplasms diagnosis   drug therapy   genetics   MeSH
• Neoplasm Staging MeSH
• Gene Expression Profiling * methods   MeSH
• Neoplasm Grading MeSH
• High-Throughput Nucleotide Sequencing * methods   MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Oncogene Proteins, Fusion MeSH
• Biomarkers, Tumor * 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