Aberrant protein expression and promoter methylation of p16 gene are correlated with malignant transformation of salivary pleomorphic adenoma

Molecular Factors in Carcinoma Ex Pleomorphic Adenoma: Systematic Review and Meta-Analysis

OBJECTIVE

Carcinoma ex pleomorphic adenoma (CXPA) is a rare malignant salivary gland tumor. Although multiple reviews have been published on salivary gland malignancies, it has been a decade since the last dedicated systematic review pertaining to CXPA alone was published. This study examines molecular factors in CXPA diagnosis.

DATA SOURCES

MEDLINE, CINAHL, Embase, Scopus, Web of Science (BIOSIS), Cochrane CENTRAL, Health Collection (Informit), OpenDOAR, and GreyNet International.

REVIEW METHODS

Systematic review and meta-analysis from inception to October 31, 2022 for all English language studies pertaining to "carcinoma ex pleomorphic adenoma." Predicted incidence of each biomarker was calculated with meta-analysis. Comparison against pleomorphic adenoma (PA) and salivary duct carcinoma (SDC) when reported within the same study are performed. Risk of bias performed with JBI tool for prevalence studies.

RESULTS

Of 19151 unique studies undergoing abstract screening, 55 studies (n = 1322 patients) underwent data analysis. Biomarkers with >3 studies were p53, HER2, AR, EGFR, PLAG1, ERBB, ER, PR, HMGA2, p16, p63, a-SMA, RAS, PTEN, PDL1, BRAF, PIK3CA, and c-kit. Highest incidence was seen in AR, EGFR, p16, and p53. Significant differences were demonstrated compared with PA and SDC. There was high heterogeneity and overall high risk of bias within studies.

CONCLUSION

Molecular factors are an area of interest in the diagnosis of CXPA. Our study results support examining CXPA as a discrete cohort in future targeted therapy trials. Laryngoscope, 134:1042-1053, 2024.

Role of Histone Deacetylases in the Pathogenesis of Salivary Gland Tumors and Therapeutic Targeting Options

Salivary gland tumors (SGTs) comprise a rare and heterogenous category of benign/malignant neoplasms with progressively increasing knowledge of the molecular mechanisms underpinning their pathogenesis, poor prognosis, and therapeutic treatment efficacy. Emerging data are pointing toward an interplay of genetic and epigenetic factors contributing to their heterogeneity and diverse clinical phenotypes. Post-translational histone modifications such as histone acetylation/deacetylation have been shown to actively participate in the pathobiology of SGTs, further suggesting that histone deacetylating factors (HDACs), selective or pan-HDAC inhibitors (HDACis), might present effective treatment options for these neoplasms. Herein, we describe the molecular and epigenetic mechanisms underlying the pathology of the different types of SGTs, focusing on histone acetylation/deacetylation effects on gene expression as well as the progress of HDACis in SGT therapy and the current status of relevant clinical trials.

The Epigenesis of Salivary Glands Carcinoma: From Field Cancerization to Carcinogenesis

Salivary gland carcinomas (SGCs) are a diverse collection of malignant tumors with marked differences in biological activity, clinical presentation and microscopic appearance. Although the etiology is varied, secondary radiation, oncogenic viruses as well as chromosomal rearrangements have all been linked to the formation of SGCs. Epigenetic modifications may also contribute to the genesis and progression of SGCs. Epigenetic modifications are any heritable changes in gene expression that are not caused by changes in DNA sequence. It is now widely accepted that epigenetics plays an important role in SGCs development. A basic epigenetic process that has been linked to a variety of pathological as well as physiological conditions including cancer formation, is DNA methylation. Transcriptional repression is caused by CpG islands hypermethylation at gene promoters, whereas hypomethylation causes overexpression of a gene. Epigenetic changes in SGCs have been identified, and they have been linked to the genesis, progression as well as prognosis of these neoplasms. Thus, we conduct a thorough evaluation of the currently known evidence on the involvement of epigenetic processes in SGCs.

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.

Global DNA Methylation Profiling Reveals Differentially Methylated CpGs between Salivary Gland Pleomorphic Adenomas with Distinct Clinical Course

Pleomorphic adenomas (PAs) are the most frequently diagnosed benign salivary gland tumors. Although the majority of PAs are characterized by slow growth, some develop very fast and are more prone to recur. The reason for such differences remains unidentified. In this study, we performed global DNA methylation profiling using the Infinium Human Methylation EPIC 850k BeadChip Array (Illumina) to search for epigenetic biomarkers that could distinguish both groups of tumors. The analysis was performed in four fast-growing tumors (FGTs) and four slow-growing tumors (SGTs). In all, 85 CpG dinucleotides differentiating both groups were identified. Six CpG tags (cg06748470, cg18413218, cg10121788, cg08249296, cg18455472, and cg19930657) were selected for bisulfite pyrosequencing in the extended group of samples. We confirmed differences in DNA methylation between both groups of samples. To evaluate the potential diagnostic accuracy of the selected markers, ROC curves were constructed. We indicated that CpGs included in two assays showed an area under the curve with an acceptable prognostic value (AUC > 0.7). However, logistic regression analysis allowed us to indicate a more optimal model consisting of five CpGs ((1) cg06748470, (2) cg00600454, (3) CpG located in chr14: 77,371,501−77,371,502 (not annotated in GRCh37/hg19), (4) CpG2 located in chr16: 77,469,589−77,469,590 (not annotated GRCh37/hg19), and (5) cg19930657) with AUC > 0.8. This set of epigenetic biomarkers may be considered as differentiating factors between FGT and SGT during salivary gland tumor diagnosis. However, this data should be confirmed in a larger cohort of samples.

Myoepithelial Carcinoma Ex Pleomorphic Adenoma of the Maxillary Sinus: A Case Report and Review of Literature

Myoepithelial carcinoma ex pleomorphic adenoma is defined as a malignant epithelial neoplasm arising from a primary or recurrent benign pleomorphic adenoma. This type of tumor comprises 3.6% of all salivary gland tumors and 12% of malignant ones. Clinically, it most commonly presents as a firm mass in the parotid gland. The development of this neoplasm in the sinonasal and nasopharyngeal regions is extremely rare and only few cases are reported in the literature. The prognosis of myoepithelial carcinoma is variable. Marked cellular pleomorphism, high mitotic rate, and high proliferative activity correspond to a poor prognosis. In this article, the authors report the histopathological features of a clinical case of a 64-years-old patient with a large median maxillary neoplasm diagnosed as myoepithelial carcinoma/ex-pleomorphic adenoma. The tumor was resected and subjected to secondary reconstruction using a revascularized free fibula flap. The myoepithelial derivation of neoplastic cells was demonstrated by immunohistochemical positivity for S-100 protein (strong and diffuse), cytokeratin 14 (strong and diffuse), and GFAP (focal).

A Rare De Novo Myoepithelial Carcinoma Ex Pleomorphic Adenoma in a Young Woman

Carcinoma ex pleomorphic adenoma, an uncommon neoplasm of the parotid gland, accounts for less than 4% of salivary gland tumors. It arises from a benign pleomorphic adenoma presenting in the sixth to eighth decades of life. We present this as a unique account of a primary parotid gland carcinoma, arising from myoepithelial cells, without a known precursor lesion, in a 28-year-old woman. This presentation seeks to provide familiarity of an unusual presentation of an unexpected rare pathology in a young female patient and the tools utilized for an accurate diagnosis.

Epigenetic alterations in salivary gland tumors

Salivary gland tumors (SGTs) comprise a heterogeneous group of benign and malignant neoplasms that exhibit significant variability in their microscopic appearance, clinical presentation, and biological behavior. The etiologic factors are unknown; however, chromosomic translocation, secondary radiation, and chemotherapy can be associated with the development of SGT. It has been indicated that epigenetic alterations can be responsible for the development and progress of these neoplasms. The epigenetic mechanisms are defined as a set of DNA changes that do not alter the sequence of nucleotide bases but alter the expression of the proteins. These alterations have been studied in the SGT, and they were associated with the development and progress of these neoplasms and may influence on SGT prognosis. Hence, we critically review the currently available data on the participation of epigenetic events on salivary gland tumors.

Promoter hypermethylation may contribute to E‑cadherin repression in the human salivary carcinoma ex pleomorphic adenoma

The role of promoter methylation in the inactivation of E‑cadherin (CDH1) in salivary carcinoma ex pleomorphic adenoma (CXPA) is unknown. The objective of this study was to determine the role and potential clinical implications of CDH1 promoter methylation in salivary CXPA. The CDH1 promoter methylation status was determined by bisulfite sequencing PCR in 37 primary CXPA tissues and 2 CXPA cell lines. E‑cadherin expression levels were determined by immunohistochemical analysis of each tumor. E‑cadherin protein levels and CDH1 mRNA levels were examined by immunoblotting and quantitative real-time PCR, respectively, in 2 CXPA cell lines. Cells were treated with 5‑Aza-dC or TGF‑β1 to test the influence of promoter methylation on CDH1 mRNA and protein expression. Associations between CDH1 molecular alterations and patients' clinicopathologic characteristics and prognosis were statistically evaluated. CDH1 promoter hypermethylation was detected in 21 of 37 tumors (56.76%). Of these 37 tumors, 13 tumors (35.14%) showed low E‑cadherin expression. Tumors that had CDH1 promoter methylation had a histological tendency toward luminal differentiation (P=0.004), high tumor grade (P=0.005), high T stage (P=0.024) and high TNM stage (P=0.038) compared with tumors that did not. The two CXPA cell lines exhibited an inverse relationship between CDH1 promoter methylation status and CDH1 mRNA and protein expression. Treatment of the hypermethylated cell line with 5‑Aza-dC restored CDH1 mRNA and E‑cadherin protein expression. The induction of hypermethylation by TGF‑β1 resulted in the repression of CDH1 mRNA and protein expression. CDH1 is commonly silenced in CXPA through promoter methylation. CDH1 methylation is closely related to tumor cell differentiation, histological grade, lymph node metastasis and advanced TNM stage, indicating that CDH1 methylation may play a role in the initiation and progression of CXPA.

DNA methylation polymerase chain reaction (PCR) array of apoptosis-related genes in pleomorphic adenomas of the salivary glands

OBJECTIVE

The aim of this study was to evaluate the DNA methylation profile in 22 apoptosis-related genes in pleomorphic adenomas (PAs) of the salivary glands, in comparison with normal salivary glands (NSGs), and to address the differences in methylation patterns between smaller and larger tumors. Additionally, we investigated if the hypermethylation of differentially methylated genes between NSGs and PAs impacted the messenger RNA (mRNA) transcription.

DESIGN

Twenty-three fresh PA samples and 12 NSG samples were included. The PA samples were divided into 2 groups: PAs with clinical size larger than 2 cm (n = 12) and PAs with clinical size 2 cm or smaller (n = 11). DNA methylation at the promoter region of a panel of 22 genes involved in apoptosis was profiled by using a human apoptosis DNA methylation polymerase chain reaction array, and the transcriptional levels of genes showing differential methylation profiles between PAs and NSGs were assessed.

RESULTS

TNFRSF25 and BCL2 L11 were highly methylated in PAs, in comparison with NSGs, irrespective of tumor size. However, no difference could be observed in the mRNA transcription between PAs and NSGs.

CONCLUSIONS

Hypermethylation of the proapoptotic genes BCL2 L11 and TNFRSF25 is observed in PA. However, this phenomenon did not impact mRNA transcription.

ADAR1 Activation Drives Leukemia Stem Cell Self-Renewal by Impairing Let-7 Biogenesis

Post-transcriptional adenosine-to-inosine RNA editing mediated by adenosine deaminase acting on RNA1 (ADAR1) promotes cancer progression and therapeutic resistance. However, ADAR1 editase-dependent mechanisms governing leukemia stem cell (LSC) generation have not been elucidated. In blast crisis chronic myeloid leukemia (BC CML), we show that increased JAK2 signaling and BCR-ABL1 amplification activate ADAR1. In a humanized BC CML mouse model, combined JAK2 and BCR-ABL1 inhibition prevents LSC self-renewal commensurate with ADAR1 downregulation. Lentiviral ADAR1 wild-type, but not an editing-defective ADAR1(E912A) mutant, induces self-renewal gene expression and impairs biogenesis of stem cell regulatory let-7 microRNAs. Combined RNA sequencing, qRT-PCR, CLIP-ADAR1, and pri-let-7 mutagenesis data suggest that ADAR1 promotes LSC generation via let-7 pri-microRNA editing and LIN28B upregulation. A small-molecule tool compound antagonizes ADAR1's effect on LSC self-renewal in stromal co-cultures and restores let-7 biogenesis. Thus, ADAR1 activation represents a unique therapeutic vulnerability in LSCs with active JAK2 signaling.

A low percentage of HER-2 amplification whereas indicates poor prognosis in salivary carcinoma ex pleomorphic adenoma: a study of 140 cases

BACKGROUND

Human epidermal growth factor receptor 2 (HER-2) has been found in many malignant tumours including salivary malignancy. HER-2-targeted therapy has been applied in the treatment of HER-2-overexpressing carcinoma. The aim of this study was to determine the status of HER-2 in salivary invasive carcinoma ex pleomorphic adenoma (ICXPA) in a relatively large Chinese sample, which may provide HER-2-targeted therapy with profound support in the future.

METHODS AND RESULTS

We collected 140 ICXPAs and their related clinicopathological and follow-up data. All cases were examined for HER-2 expression by immunohistochemistry and gene amplification by fluorescence in situ hybridization, if necessary. The study showed that the ratio of HER-2 positivity was only 25% (35/140) in all cases, but the positive ratio in ICXPAs with luminal differentiation for malignant component (32/79, 40.5%) was much higher than that in cases with non-luminal differentiation (3/61, 4.9%). The overexpression of HER-2 was closely associated with gender, histological grade and N stage. HER-2-positive tumours conferred short overall survival time (P = 0.036) and short disease-specific survival time (P = 0.042) in patients, but HER-2 status was not an independent predictor of prognosis.

CONCLUSIONS

Human epidermal growth factor receptor 2 amplification is significantly associated with cell differentiation of the malignant component in ICXPA and it implies an unfavourable prognosis. Although HER-2 positivity is not common in the tumour, HER-2-targeted therapy for those HER-2-positive patients is still worth expecting.

Dysregulation of the Rb pathway in recurrent pleomorphic adenoma of the salivary glands

Pleomorphic adenoma (PA) is the most common salivary gland neoplasm, and while mostly benign, recurrences (RPA) and malignant transformation to carcinoma ex-PA (CXPA) do occur. Cell cycle proteins important in its tumorigenesis have been studied as markers for PA with a high risk of RPA or CXPA. The aim of the present study was to investigate cell cycle markers p-16, cyclin D1, CDK4, E2F, and retinoblastoma (Rb) in this context. Expression of p16, cyclin D1, E2F, CDK4, and Rb was studied by immunohistochemistry in 24 cases of PA, 21 of RPA, and 2 of CXPA. The presence of HPV was assessed by in situ hybridization. Immunostaining for p16 and cyclin D1 was negative or weakly positive in most cases of PA while strongly positive in the majority of RPA and both CXPA cases. Staining for Rb and CDK4 was either negative or weakly positive in PA, RPA, and CXPA. Expression of E2F was stronger in RPA and CXPA than in PA. Nuclear reactivity for HPV was not observed in any case. In conclusion, the strong staining for p16, cyclinD1, and E2F in RPA and CXPA, while weak or negative in PA, suggests that these proteins might be involved in recurrence and malignant transformation of PA.

Cyclin-dependent kinase inhibitors, p16 and p27, demonstrate different expression patterns in thymoma and thymic carcinoma

OBJECTIVES

The role of cell cycle inhibitors in tumorigenesis has been proven in various neoplasms; however, their roles in thymic tumors are still unclear. We examined the expression of cell cycle inhibitors such as those of the Cip/Kip family (p21, p27, and p57) and the INK-4/ARF family (p16 and p14) in thymoma and thymic carcinoma.

METHODS

Samples from 41 thymoma and 14 thymic carcinoma patients, and 34 normal thymic tissue samples were prepared for the study. Immunohistochemical analysis using antibodies to p21, p27, p57, p16, and p14 was carried out, and the positivity for these inhibitors in each group was estimated in terms of their subcellular location and percentage of cells showing positive staining.

RESULTS

Nuclear p27 showed a stepwise decrease (p < 0.0001), and the cytoplasmic p27 showed a stepwise increase (p < 0.0001) in expression level with the increase in malignancy. p16 in both the nucleus and cytoplasm showed a stepwise increase (p < 0.0001) in expression level with the increase in malignancy. However, as for p21, p57, and p14, there was almost no nuclear or cytoplasmic expression in each group.

CONCLUSIONS

Our findings suggest that low nuclear and high cytoplasmic p27 expression levels, and high nuclear and cytoplasmic p16 expression levels may correlate with the increase in thymic malignancy.

Immunohistochemical expression of p16 in Carcinoma Ex-pleomorphic Adenoma (undifferentiated and Adenocarcinoma Types)

OBJECTIVE

This study was aimed at characterizing alterations in the immunohistochemical expression of p16 in carcinoma ex-pleomorphic adenomas.

STUDY DESIGN

A selected series of 27 cases of carcinoma ex-pleomorphic adenomas were examined.

RESULTS

The results showed that p16 expression in non tumour duct cells was strongly positive nuclear staining in 23 (85%) cases out of 27 cases, that 3 (11.1%) had moderate staining, and that 1 (3.7%) had weak staining. p16 expression in carcinoma ex-pleomorphic adenomas was indicated as a negative nuclear staining in 22 (81.4%) cases out of 27cases, and 5 (18.5%) cases expressed moderate staining.

CONCLUSION

This study suggests that alteration of p16 expression is detected in carcinoma ex-pleomorphic adenomas. p16 has a role in development of carcinoma ex-pleomorphic adenomas.

Metastasizing pleomorphic adenoma: a fascinating enigma

Among salivary gland neoplasms, metastasizing pleomorphic adenoma (MPA) constitutes an extremely rare group of tumors. The present paper reports a case of pleomorphic adenoma (PA) in submandibular gland that, after more than 30 years of initial treatment, recurred and metastasized to ipsilateral neck lymph nodes and parotid gland. In an attempt to elucidate the malignant behavior of metastasizing pleomorphic adenoma, we performed Ki-67, p53, p16, and bcl-2 immunohistochemistry staining of our case sample. Many immunohistochemistry staining studies have been done on malignant salivary gland tumors. However, to the best of our knowledge no immunohistochemistry staining of the aforementioned markers has been previously performed on metastasizing pleomorphic adenoma.