Functional Histology of Salivary Gland Pleomorphic Adenoma: An Appraisal

Insights into the molecular alterations of PLAG1 and HMGA2 associated with malignant phenotype acquisition in pleomorphic adenoma

Pleomorphic adenoma (PA) is the most common neoplasm of the salivary gland, presenting with a variety of histological features. In some cases, PA can undergo malignant transformation to carcinoma ex pleomorphic adenoma (CXPA). The transition from PA to CXPA is associated with complex molecular alterations, particularly involving the pleomorphic adenoma gene 1 (PLAG1) and high mobility group protein gene (HMGA2). This review investigates the molecular alterations of PLAG1 and HMGA2 in all domains in the malignant transformation of PA. Our analysis highlights that these markers are key alterations in the etiopathogenesis of PA and CXPA, with gene fusion and amplification being frequently reported mechanisms. Although the exact role of PLAG1 and HMGA2 in the oncogenic process remains unclear, further studies on the HMGA2 and PLAG1, are needed particularly in HMGA2-PLAG1-IGF2 which is proving to be a potential pathway for the development of clinically applicable therapies, especially for CXPA management.

Is epithelial-mesenchymal transition related to the biological behavior of salivary gland neoplasms?

OBJECTIVE

To evaluate and compare the expression of E-cadherin, Snail1 and Twist1 in pleomorphic adenomas (PAs), adenoid cystic carcinomas (AdCCa) and carcinoma ex-pleomorphic adenomas (CaexPA) of salivary glands, as well as investigate possible associations with clinicopathological parameters.

STUDY DESIGN

E-cadherin, Snail1 and Twist1 antibody immunostaining were analyzed semiquantitatively in 20 PAs, 20 AdCCas and 10 CaexPAs. Cases were classified as low and high expression for analysis of the association with clinicopathological parameters.

RESULTS

Compared to PAs, AdCCas and CaexPAs exhibited higher nuclear expression of Snail1 (p = 0.021 and p = 0.028, respectively) and Twist1 (p = 0.009 and p = 0.001). Membranous and cytoplasmic expression of E-cadherin were positively correlated in PAs, AdCCas and CaexPAs (r = 0.645, p = 0.002; r = 0.824, p < 0.001; r = 0.677, p = 0.031). In PAs, positive correlation was found between nuclear expression of Snail1 and membrane expression of E-cadherin (r = 0.634; p = 0.003), as well as between nuclear expression of Snail1 and Twist1 (r = 0.580; p = 0.007). Negative correlations were detected between membrane expression of E-cadherin and cytoplasmic expression of Snail1 in AdCCas (r = - 0.489; p = 0.029).

CONCLUSIONS

E-cadherin, Twist1, and Snail1 may participate in modulating events related to cell differentiation and adhesion in PAs and to biological behavior in AdCCas and CaexPAs, which indicates the involvement of EMT in these processes. Furthermore, the expression of these proteins in these carcinomas may reflect the plasticity feature of EMT.

Oral cavity salivary gland pleomorphic adenoma: a histomorphological case series

BACKGROUND

Pleomorphic adenoma (PA), the most common benign salivary gland epithelial lesion, has a biphasic epithelial-mesenchymal pattern and great histopathological diversity.

METHODS

This study's objective was to conduct a retrospective clinicopathological analysis, focusing on the histopathology characteristics of salivary gland PA.

RESULTS

There were ten cases of pleomorphic adenoma. The mean age was 33.5 years and no gender predilection was observed. All the patients presented with an asymptomatic mass and the duration of presentation was 31.2 ± 19.4 months. The cellular subtype (50 %) of PA was the most common. Capsular infiltration and incomplete capsules occurred in 20 % of cases. All the cases had round (100 %) and myxoid stroma. The cellular subtype was more common in the major salivary glands; showed capsular abnormalities (incomplete capsule, absent capsule, and tumor infiltration); and had more plasmacytoid, angular, spindled non-luminal cells as well as inflammation and cystic degeneration. The classic subtype had more clear and oncocytic cells along with sebaceous and squamous differentiation. The stroma-rich subtype had the shortest duration of complaints (three months) and showed giant cell reaction.

CONCLUSIONS

These findings confirm previous studies on the clinicopathological features of pleomorphic adenomas and highlight important morphologic characteristics like capsular invasion and squamous metaplasia, which can otherwise indicate malignancy.

Influence of p16 Protein Immunostaining on Histopathological Features of Pleomorphic Adenoma and Carcinoma ex- Pleomorphic Adenoma

The objective of this study was to evaluate the role of p16 in histologic characteristics and transition of Pleomorphic Adenoma (PA) to Carcinoma ex-PA (CxPA). So, 60 PA and 4 CxPA were histologic reviewed based on microscopic characteristics proposed by Hellquist, Triantafyllou and Dulguerov (PA) and Morais, Antony and Toluie (CxPA). Immunostaining for p16 was associated in different parenchyma and stroma of both tumors and Fisher's/chi-square tests and Mann-Whitney test were performed (SPSS v20.0, p<0.05). In PA the periductal cells were predominantly p16- and that ductal and myoepithelial cells showed a significant increase in p16+ cells (p<0.001). In CxPA, none of the cases showed p16+ in periductal cells, most parotid cases showed p16+ in ductal cells, and one case of parotid and the submandibular case showed mild immunostaining for myoepithelial cells. There was a small reduction in p16+ in CxPA compared to PA (p=0.537), but in both tumors there was less p16+ cells in solid stroma than other (p<0.001). The p16+ cases of PA had a higher capsular thickness (p=0.047). So, the loss of p16 immunostaining does not seem to be associated with the transition from PA to CxPA, but in both tumors the loss of p16+ cells are related to microscopic aggressiveness.

Top Ten Differentials to Mull Over for Head and Neck Myoepithelial Neoplasms

BACKGROUND

Myoepithelial neoplasms of the salivary gland are benign or malignant neoplasms composed exclusively of neoplastic myoepithelial cells. These tumors, including the benign myoepithelioma and the malignant counterpart myoepithelial carcinoma, exhibit a wide range of cytomorphologic features and architectural patterns.

METHODS

Review.

RESULTS

Myoepithelial cells can be epithelial, plasmacytoid, clear cell, spindle cell, and/or oncocytic cell, arranging as trabeculae, solid sheets, nests, cords, and/or single cells. A stromal component is commonly but not universally present, Therefore, their differential diagnoses are quite broad, including salivary gland neoplasms especially those with a myoepithelial component, plasmacytoma, melanoma, and various mesenchymal tumors.

CONCLUSION

In this review, we summarize the characteristic histologic features, useful immunohistochemical panel, and common molecular alterations of myoepithelial tumors and their top differential diagnoses. A logical stepwise algorithmic approach and an immunohistochemical panel to include multiple myoepithelial markers are essential to establish the correct diagnosis.

Simultaneous Expression of PD-1 and PD-L1 in Peripheral and Central Immune Cells and Tumor Cells in the Benign and Malignant Salivary Gland Tumors Microenvironment

BACKGROUND

To investigate the differential expression of PD-1 and PD-L1 in salivary gland tumors (SGTs, malignant and benign subtypes) and determine their association with the clinicopathological characterization of the patients.

METHODS

The immunohistochemistry was used to examine PD-1 and PD-L1 expression in specimens from 83 patients with primary SGTs including salivary ductal carcinoma (SDC), adenoid cystic carcinoma (AdCC), acinic cell carcinoma (ACC), mucoepidermoid carcinoma (MEC), warthin's tumors (WT), poleomorphic adenoma (PA) and other subtypes.

RESULTS

The expression of PD-1 in peripheral and central immune cells (ICs) of MEC, and peripheral ICs of ACC was significantly higher than those with AdCC (P = 0.02, P = 0.02, P = 0.03, respectively). Interestingly, the expression of PD-1 was also observed in peripheral and central malignant tumor cells (TCs), particularly in SDC and ACC. Despite no significant difference in PD-L1 expression of TCs among malignant subtypes, the peripheral and central ICs of ACC and MEC were revealed to express PDL-1 significantly more than those with AdCC (P < 0.05). WTs were rich in PD-1/PD-L1 expressing ICs. However, the tumor microenvironment of PA generally had low levels of PD-1/PD-L1 expression. In general, the expression of PD-1 in peripheral and central TCs was found to be significantly higher in malignant tumors than in benign ones (P = 0.002 and P = 0.003, respectively).

CONCLUSION

The simultaneous presentation of PD-1 and PD-L1 in TCs and ICs of SGTs, their significant association with disease severity as well as the positive correlation between these immune checkpoints may suggest the therapeutic potential of anti-PD-1 and anti-PDL-1 combinational immunotherapy for SGTs.

Pleomorphic Adenoma of the Salivary Glands and Epithelial–Mesenchymal Transition

Pleomorphic adenoma (PA) is a localized tumor that presents pleomorphic or mixed characteristics of epithelial origin and is interwoven with mucoid tissue, myxoid tissue, and chondroid masses. The literature reported that PA most often occurs in adults aged 30–60 years and is a female predilection; the exact etiology remains unclear. Epithelial–mesenchymal transition (EMT) is the transdifferentiation of stationary epithelial cells primarily activated by a core set of transcription factors (EMT-TFs) involved in DNA repair and offers advantages under various stress conditions. Data have suggested that EMTs represent the basic principle of tissue heterogeneity in PAs, demonstrating the potential of adult epithelial cells to transdifferentiate into mesenchymal cells. It has also been reported that multiple TFs, such as TWIST and SLUG, are involved in EMT in PA and that SLUG could play an essential role in the transition from myoepithelial to mesenchymal cells. Given this background, this review aims to summarize and clarify the involvement of EMT in the development of PA, chondrocyte differentiation, and malignant transformation to contribute to the fundamental elucidation of the mechanisms underlying EMT.

SLUG is a key regulator of epithelial-mesenchymal transition in pleomorphic adenoma

The histogenesis of pleomorphic adenoma (PA) of the salivary glands remains controversial. PAs are characterized by the transition of epithelial cells to spindled mesenchymal cells, known as epithelial-mesenchymal transition (EMT). The present study aimed to identify a major EMT-inducing transcription factor (EMT-TF) in PAs. Real-time PCR analysis of SNAIL, SLUG, ZEB1, and TWIST1 demonstrated that only SLUG was significantly upregulated in normal salivary glands and PAs. Combined in situ hybridization for SLUG and multiplex immunohistochemistry for CK19 and P63 revealed that SLUG was specifically expressed in the myoepithelial cells of normal salivary glands. In PAs, SLUG was expressed in neoplastic myoepithelial cells and stromal cells but not in the luminal cells lining the inner layers of tumor glands. SLUG expression showed no correlation with PLAG1 expression, and in vitro experiments demonstrated that PLAG1 suppression in primary cultured PA cells or PLAG1 overexpression in HEK 293 T cells did not affect SLUG levels, indicating that PLAG1 was not involved in the upregulation of SLUG in PAs. The suppression of SLUG expression in cultured PA cells resulted in a morphology change to a less elongated shape and attenuated tumor growth. In addition, SLUG downregulation led to increased E-cadherin and decreased N-cadherin and vimentin expression levels along with decreased migratory activity in cultured PA cells. These findings suggest that SLUG is a major TF that can induce EMT in PAs. In summary, SLUG is specifically and highly expressed in the myoepithelial cells and stromal cells of PAs and is a key regulator of EMT in PAs.

Evaluation of immunohistochemical expression of E-cadherin in pleomorphic adenoma and adenoid cystic carcinoma

Background:

Pleomorphic adenoma (PA) and adenoid cystic carcinoma (ADCC) are benign and malignant salivary gland tumors, respectively, with distinct behavior. They have similar origins and cell components. E-cadherins are the main homophilic cell adhesion molecules, which play a central role in maintaining epithelial integrity, functioning in intercellular adhesion and differentiation. Hence, changes in E-cadherin function are reflected in the morphologic events associated with the cellular arrangement, movement and wound healing.

Aim:

To study and compare the expression of E-cadherin immunostaining in PA and ADCC.

Materials and Methods:

Fifteen cases of each PA and ADCC were immunohistochemically stained with E-cadherin. Five cases of normal salivary gland tissues were taken as the positive control.

Mann–Whitney U-test was used for statistical analysis.

Results:

About 86.6% of PA cases showed homogeneous staining. 66.6% of cases of ADCC showed heterogeneous staining. PA, cribriform and tubular patterns of ADCC predominantly showed moderate immune-staining and solid patterns of ADCC exhibited predominantly mild immunostaining. Depending on the intensity of staining, we found a significant P value between PA and the solid variant of ADCC.

Conclusion:

E-cadherin proved to be a better marker for epithelial phenotypes in PAs. In ADCC difference in staining intensity between different histological subtypes suggests that further studies should be done to assess the usefulness of an immuno-marker to know the aggressive behavior of ADCC.

Pleomorphic Adenoma of the Parotid Gland and the Parapharyngeal Space: Two Diametrically Opposing Surgical Philosophies for the Same Histopathologic Entity?

BACKGROUND

The aim of this study was to investigate the histopathologic findings in parotid and parapharyngeal pleomorphic adenomas and draw conclusions concerning the surgical strategy.

METHODS

Retrospective study of medical charts of patients with resected pleomorphic adenomas (PA) between 2005 and 2020 at two tertiary medical referral centers. Histologic specimens were reexamined by an experienced head and neck pathologist. Patients with insufficient/incomplete data were excluded from our study sample.

RESULTS

A total of 844 patients formed our study sample (291 men, 553 women, average age 48.9 years); 786 cases had a PA in the parotid gland (PG) (93.1%), and the remaining 58 cases had a PA in the parapharyngeal space (PS) (6.9%). Recurrences were detected in 8/844 cases (7/786 in the PG, 1/58 in the PS, 0.94% in total) with a mean follow-up time of 86.7 months (10-189 months) with no statistically significant differences between the study groups (p = 0.527). Our analysis showed that parapharyngeal pleomorphic adenomas are characterized by a lower incidence of an intact anatomical capsule (71.4% vs. 82.6%, p = 0.035) and a remarkably more frequent occurrence of satellite nodules (20.7% vs. 7.5%, p < 0.001).

CONCLUSIONS

The more challenging histopathologic profile of parapharyngeal pleomorphic adenomas points towards the fact that parapharyngeal surgery should remain in the hands of experienced surgeons at high-volume centers.

Degenerative nuclear atypia in pleomorphic adenoma of salivary glands: Histological and immunohistochemical observations

The occurrence and topographical distribution of nuclear changes regarded as degenerative were examined in 84 salivary pleomorphic adenomas (PAs). Haematoxylin and eosin-stained sections from them were light-microscopically studied for unusual variations in size, shape and chromatin pattern of tumour-cell nuclei. Selected cases were further examined by immunohistochemical techniques valuable in characterising cell phenotypes in PA, and cell cycle antigens. A single case (female, 26 years, palate; 1.2 %) showed prominent cells with eosinophilic cytoplasm and variably enlarged or giant, irregularly shaped and occasionally multi-vacuolated nuclei with condensed or stippled chromatin and no mitoses. These cells were variably dyscohesive and did not line lumina; were cytokeratins 5/6, 7 and 14 (+, cytoplasmic), smooth muscle actin (+, cytoplasmic), p63 (+, nuclear), S-100 protein (+, nuclear and cytoplasmic), and WT1 and podoplanin (+/-, cytoplasmic); and did not stain for DOG1, CD63, p16 or Ki67. The nuclear vacuoles were cytokeratin and WT1 (+) - hence, interpreted as cytoplasmic inclusions. Degenerative nuclear atypia in PA seems rare, associated with non-cycling, non-luminal cells of myomatous ('myoepithelial') or schwannomatous phenotype and not related to malignant transformation. The particular phenotype of the affected cells suggests similarities to the degenerative nuclear atypia in pleomorphic leiomyoma and ancient schwannoma.

Navigating small biopsies of salivary gland tumors: a pattern-based approach

Diagnosis of salivary gland tumors on small biopsy can be difficult because of overlapping morphology, limited tissue availability, and technical artifact. Although a specific diagnosis is not feasible in all cases, a cautious and thoughtful approach to the differential diagnosis and a keen awareness of clinical consequences can facilitate the most complete and useful classification possible. In this review, we present a general strategy for the evaluation of small salivary biopsies, including consideration of clinical and radiographic information, systematic assessment of histologic patterns, and judicious use of immunohistochemistry and molecular studies. We then focus on the distinctive differential diagnoses raised by 6 specific histologic patterns: tubular and cribriform architecture, squamous differentiation, mucin and other secretions, high-grade cytology, epithelial and lymphoid elements, and oncocytic features. Throughout this systematic and pattern-based approach, we focus on practical and cost-effective strategies to overcome the most common diagnostic challenges in limited material.

Plasmacytoid cells in salivary pleomorphic adenoma: an alternative interpretation of their immunohistochemical characteristics highlights function and capability for epithelial-mesenchymal transition

OBJECTIVES

Plasmacytoid cells (PLCs) in salivary pleomorphic adenoma (SPA) are regarded as modified neoplastic myoepithelia and define plasmacytoid myoepithelioma (pMYO). However, histochemically, immunohistochemically and ultrastructurally, PLCs fail to demonstrate frank myogenous properties. Epithelial-mesenchymal transition (EMT) may explain the phenotypes in SPA. Our aim was to evaluate (1) PLCs with accepted or purported myoepithelial and EMT-related markers; and (2) pMYOs for PLAG1 aberrations by using fluorescence in situ hybridization.

STUDY DESIGN

Eight SPAs with or without PLC-predominance and 3 pMYOs were immunohistochemically studied.

RESULTS

PLCs in SPA and pMYO exhibited strong, scattered to diffuse positivity for K7, rare K14 positivity and were mostly negative for α-smooth muscle actin, h-caldesmon, and p63/p40. S100 staining was strong and diffuse, whereas calponin was variable. DOG1 was negative. PLCs in pMYO and PLC-rich SPA exhibited selective or diffuse WT1 and D2-40 immunoreactivity. EMT markers SNAIL/SLUG exhibited strong and variable immunoreactivity in PLCs in contrast to weak or absent E-cadherin expression. SOX10 was diffusely and strongly positive. PLAG1 rearrangement was present in 1 pMYO.

CONCLUSIONS

PLCs mostly fail to express myoepithelial markers; PLCs are neoplastic cells adapting to microenvironmental changes and capable of EMT; and tumors composed solely of PLCs are apparently SPAs depleted of a ductal component.

Parotid pleomorphic adenomas: Factors influencing surgical techniques, morbidity, and long-term outcome relative to the new ESGS classification in a retrospective study

PURPOSE

To assess long-term results after treatment of parotid pleomorphic adenomas (PPAs) with different surgical techniques, standardized according to the European Salivary Gland Society (ESGS) classification system.

METHODS

We analyzed ESGS categories, occurrence of facial nerve paresis (FNP), Frey's syndrome, histopathology, and recurrences. Surgical modalities were compared, differentiating techniques with and without facial nerve dissection. A strict protocol ensured a postoperative follow-up-period of more than 7 years.

RESULTS

205 patients were included. A complete follow-up was possible in 138 patients, 77 of whom underwent extracapsular dissection (ED) and 61 of whom had other surgical modalities (OSMs). ESGS categories correlated with the extent of surgery, significantly with the risk for FNP and Frey's syndrome, but not with recurrences. Recurrences did not differ significantly between ED and OSMs, whereas the risks for FNP (p < 0.001 each) and Frey's syndrome (p = 0.000) were significantly higher after OSMs in comparison with ED. Young women with a stroma-rich (myxoid) tumor subtype appear to have the greatest risk for recurrences.

CONCLUSION

ED is the treatment of choice for PPAs, if possible, resulting in similar recurrence rates but significantly fewer comorbidities in comparison with more extensive surgery. After the treatment of PPAs, a long-term follow-up is needed, including imaging.

A rare ectopic localization of pleomorphic adenoma

INTRODUCTION

Pleomorphic adenoma (PA) is the most common benign salivary gland tumor, frequently affecting the major salivary glands but also the palatal or labial minor salivary glands. Pleomorphic adenomas affecting the retromolar trigone have seldom been reported with only few cases described in the literature.

OBSERVATION

We present the case of a young female patient who presented with this rare localization of pleomorphic adenoma and its subsequent management.

DISCUSSION

Pleomorphic adenoma of the retromolar trigone is a rare occurrence. Nevertheless, when faced with a swelling of the retromolar trigone, a diagnosis of pleomorphic adenoma should not be omitted from the differential.

Divergent Schwannoma-Like Phenotype in a Pleomorphic Adenoma

The schwannoma-like pleomorphic adenoma is a rare histopathological variant of the pleomorphic adenoma. Five previous reports with seven cases exist in English language literature. These tumors present in the parotid gland most commonly. Intraparotid schwannomas of the facial nerve and schwannomas with glandular differentiation have also been reported. A 60-year-old male presented with an asymptomatic swelling over the left angle of the mandible. The swelling had been present for about 12 years with a recent increase in size. CT imaging showed a hyperdense circumscribed mass of the superficial lobe of the parotid. The working diagnosis was that of a benign tumor of salivary gland or soft tissue origin. The mass was excised with careful preservation of the facial nerve. The 3.5 cm mass was submitted for histopathological examination. The well-circumscribed, encapsulated mass showed a predominant sheet-like proliferation of Antoni type A-like tissue, Foci of glandular differentiation with duct-like structures were also seen. Cytological atypia or mitotic activity were not seen. Nuclei of lesional cells diffusely and strongly expressed reactivity to p63. The final diagnosis was a schwannoma-like pleomorphic adenoma. No recurrence has been reported in the 15 months since the removal. Facial nerve function is unimpaired with a House Brackmann facial nerve function score of one. The potential for misdiagnosis in fine needle aspirate and incisional biopsies is real in cases of schwannoma-like pleomorphic adenoma. The diagnostic pitfalls include the schwannoma and leiomyoma. Schwannomas with glandular differentiation have also been reported and therefore a misdiagnosis may potentially occur in excised specimens. Careful application of immunohistochemistry may help in the differentiation of these lesions.

Pleomorphic adenoma and adenoid cystic carcinoma of salivary glands: E-cadherin immunoexpression and analysis of the CDH1 -160C/A polymorphism

OBJECTIVE

Despite their similar cellular origin, pleomorphic adenomas (PA) and adenoid cystic carcinomas (ACC) present distinct behaviors. This study aimed to analyze the immunoexpression of E-cadherin in PA and ACC of salivary glands, and to investigate differences in its expression in relation to E-cadherin gene (CDH1) -160C/A polymorphism.

DESIGN

Twenty-four PA (15 cell-rich and 9 cell-poor tumors) and 24 ACC (10 tubular, 8 cribriform and 6 solid tumors) were selected for the analysis of pattern of distribution, and cellular localization of E-cadherin. In addition, E-cadherin expression was evaluated using the H-score scoring system. The CDH1 -160C/A polymorphism was investigated by PCR-RFLP.

RESULTS

No significant differences in pattern of distribution (p=0.181) and cellular localization (p=0.192) of E-cadherin were observed between PA and ACC. Comparison of PA and ACC cases revealed a higher median H-score in the latter (p=0.036). Cell-rich PA presented a higher H-score than cell-poor tumors (p=0.013), whereas no significant differences in E-cadherin expression were observed between ACC subtypes (p=0.254). The heterozygous genotype of the CDH1 -160C/A polymorphism was detected in only one PA and one ACC. H-scores for tumors carrying the polymorphism were below the lower quartile of their respective groups.

CONCLUSIONS

The results suggest that E-cadherin expression in PA and ACC is mainly related to cellular composition (epithelial cells versus myoepithelial cells) and degree of differentiation of myoepithelial cells in these tumors. The CDH1 -160C/A polymorphism does not seem to significantly influence the expression of E-cadherin in PA and ACC of salivary glands.