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

Basal cell adenoma (BCA) is a benign salivary neoplasm that exhibits a divergent spectrum of growth patterns, including cribriform, tubular, trabecular, membranous, and solid. A subset of BCAs is characterized by the presence of abundant S100 protein-positive stroma, which makes this variant unique and potentially represents a hybrid lesion or an entity intermediate between BCA and pleomorphic adenoma (PA). From the authors' registry, we selected 17 cases of BCA with abundant S100 protein-positive stromal components and compared them with 7 cases of BCA without S100 protein-positive stroma, and 6 cases of myoepithelial cell-rich PAs. All cases were analyzed by immunohistochemistry (IHC) using antibodies to S100 protein, SOX10, PLAG1, HMGA2, p63/p40, cytokeratins, EMA, LEF1, and/or β-catenin. Next-generation sequencing (NGS), fluorescence in situ hybridization (FISH) for the rearrangement of PLAG1, and methylation analysis were performed. The BCA S100 protein stromal cell-rich group consisted of 7 males and 10 females with an average age of 62 years. Their tumors showed typical S100 protein-positive stroma, which was also positive for SOX10 in all cases. The stromal and/or epithelial components showed expression of LEF1 and β-catenin in 17 and 15 cases, respectively. HMGA2 IHC showed nuclear expression in one case while PLAG1 was negative in all cases. In 11 cases, one or more mutations were present, including CTNNB1 mutation (n = 11). The first control cohort of BCA without S100 protein-positive stroma consisted of 1 male and 6 females with an average age of 50 years. This group showed LEF1 and nuclear β-catenin expression in 1 and 2 cases, respectively. The second control group of PA (including 4 spindle-shaped cellular and 2 oncocytic PAs) was devoid of CTNNB1 mutations. Two cases presented with gene fusions, including MEG3::PLAG1 and ACTA2::PLAG1, and an additional two cases showed PLAG1 break. It has been proposed earlier that BCA is related to PA based on a shared biphasic nature and a divergent spectrum of growth patterns. Our findings suggest that BCAs with abundant S100 protein-positive stroma are tumors that morphologically display tricellular differentiation into inner (luminal) ductal epithelial cells, outer (abluminal) basaloid myoepithelial cells, and spindle-shaped stromal S100-positive cells (stromal abluminal). According to our investigation, BCAs with S100 protein-positive stroma represent a distinctive triphasic subset of BCA, which is substantially different from PA, both in immunoprofile and molecular underpinnings.

• Keywords
• Basal cell adenoma, Methylation analysis, Molecular diagnostics, Next-generation sequencing, S100 protein–positive stroma, Salivary gland,
• Publication type
• Journal Article MeSH

PURPOSE: Pleomorphic adenoma (PA), the most common benign tumour of the parotid gland, requires accurate preoperative diagnosis owing to its capacity for malignant transformation. The aim of this study was to evaluate our experience with ultrasound-guided fine-needle aspiration biopsy (FNAB) in the diagnostic algorithm for patients with PA and to assess clinical outcomes for those with different surgical approaches. MATERIAL AND METHODS: We carried out a retrospective analysis of patients treated for parotid gland mass between 2010 and 2016. These had had preoperative FNAB and had undergone subsequent surgery. RESULTS: 165 patients had FNAB with the result of PA and the definitive histology confirmed PA in 159 cases (96.4%). On the other hand, in 179 patients, the definitive histology showed PA and the preoperative FNAB result corresponded in 159 cases (88.9%). The measured sensitivity, specificity and accuracy of ultrasound-guided FNAB in the diagnosis of PA were, respectively, 88.83%, 96.23% and 92.31%. Most of the patients underwent superficial or partial superficial parotidectomy, followed by extracapsular dissection which was associated with statistically lower risk of facial nerve injury (P=0.04). CONCLUSION: Ultrasound-guided FNAB is simple, accurate and valuable in the diagnosis of PA and provides results that can lead to the choice of less invasive operative treatment.

• Keywords
• fine-needle aspiration biopsy, parotid gland tumours, pleomorphic adenoma, ultrasound,
• MeSH
• Adult MeSH
• Ultrasonography, Interventional MeSH
• Middle Aged MeSH
• Humans MeSH
• Adolescent MeSH
• Young Adult MeSH
• Parotid Neoplasms * pathology   surgery   diagnosis   MeSH
• Parotid Gland pathology   surgery   MeSH
• Adenoma, Pleomorphic * pathology   surgery   diagnosis   MeSH
• Retrospective Studies MeSH
• Aged, 80 and over MeSH
• Aged MeSH
• Sensitivity and Specificity MeSH
• Biopsy, Fine-Needle MeSH
• Image-Guided Biopsy methods   MeSH
• Check Tag
• 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

Salivary gland tumors are a heterogeneous group of tumors originating from the major and minor salivary glands. The pleomorphic adenoma (PA), which is the most common subtype, is a benign lesion showing a remarkable morphologic diversity and that, upon recurrence or malignant transformation, can cause significant clinical problems. Cytogenetic studies of >500 PAs have revealed a complex and recurrent pattern of chromosome rearrangements. In this review, we discuss the specificity and frequency of these rearrangements and their molecular/clinical consequences. The genomic hallmark of PA is translocations with breakpoints in 8q12 and 12q13-15 resulting in gene fusions involving the transcription factor genes PLAG1 and HMGA2. Until recently, the association between these two oncogenic drivers was obscure. Studies of the Silver−Russel syndrome, a growth retardation condition infrequently caused by mutations in IGF2/HMGA2/PLAG1, have provided new clues to the understanding of the molecular pathogenesis of PA. These studies have demonstrated that HMGA2 is an upstream regulator of PLAG1 and that HMGA2 regulates the expression of IGF2 via PLAG1. This provides a novel explanation for the 8q12/12q13-15 aberrations in PA and identifies IGF2 as a major oncogenic driver and therapeutic target in PA. These studies have important diagnostic and therapeutic implications for patients with PA.

• Keywords
• HMGA2, IGF2, PLAG1, chromosome 12q13-15, chromosome 8q12, chromosome translocation, diagnostic biomarker, gene fusion, pleomorphic adenoma, therapeutic target,
• Publication type
• Journal Article MeSH
• Review MeSH