Alterations of the INK4a-ARF gene locus in pleomorphic adenoma of the parotid gland

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.

Methylation of tumour suppressor genes in benign and malignant salivary gland tumours: a systematic review and meta-analysis

The aim of the present systematic review was to critically analyse the relationship between tumour suppressor genes (TSGs) promoter methylation, a potent mechanism of gene silencing, and the development of salivary gland tumours, as well as the possible effect on clinical/histological characteristics. Review protocol was registered in the International Prospective Register of Systematic Reviews (PROSPERO) database (registration ID CRD42020218511). A comprehensive search of Web of Science, Scopus, PubMed, and Cochrane Central Register of Controlled Trials was performed utilizing relevant key terms, supplemented by a search of grey literature. Newcastle-Ottawa Quality Assessment Scale (NOQAS) was used for the quality assessment of included studies. Sixteen cross-sectional and 12 case-control studies were included in the review, predominantly dealing with methylation in TSGs related to DNA repair, cell cycle, and cell growth regulation and differentiation. Quantitative synthesis could be performed on P16 (inhibitor of cyclin-dependent kinase 4a), RASSF1A (Ras association domain family 1 isoform A) and MGMT (O6-methylguanine DNA methyltransferase) genes only. It showed that P16 and RASSF1A genes were more frequently methylated in salivary gland tumours compared to controls (P = .0002 and P < .0001, respectively), while no significant difference was observed for MGMT. Additionally, P16 did not appear to be related to malignant transformation of pleomorphic adenomas (P = .330). In conclusion, TSG methylation is involved in salivary gland tumour pathogenesis and several genes might play a considerable role. Further studies are needed for a better understanding of complex epigenetic deregulation during salivary gland tumour development and progression.

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.

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.

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

CONTEXT

The significance of promoter methylation of the p16 gene and intracellular localization of p16 protein in the carcinogenesis of salivary carcinoma ex pleomorphic adenoma (Ca-ex-PA) is not clear. The correlation of the promoter methylation of the p16 gene and the expression and localization of p16 protein in Ca-ex-PA need to be further clarified.

OBJECTIVE

To investigate the p16 protein expression and promoter methylation of p16 gene in Ca-ex-PA and their roles in the malignant transformation of pleomorphic adenoma to Ca-ex-PA.

DESIGN

The p16 protein expression and promoter methylation of the p16 gene were determined in both benign and malignant components of 50 primary salivary Ca-ex-PA tissues by immunohistochemistry and methylation-specific polymerase chain reaction. Expression of p16 protein and promoter methylation of the p16 gene between the benign and the malignant components was compared statistically.

RESULTS

The tumor cells in the malignant components showed significantly higher p16 protein expression in the cytoplasm and lower expression in the nuclei than those in the benign components. Promoter methylation frequency of the p16 gene in the malignant components (36%) was significantly higher than that in the benign components (16%). There were no correlations between p16 protein expression and promoter methylation of the p16 gene in either benign or malignant components.

CONCLUSIONS

Overexpression of p16 protein in the cytoplasm and decreased expression of p16 protein in the nucleus may play important roles in the evolution of pleomorphic adenoma to Ca-ex-PA. Promoter methylation of the p16 gene may be correlated with the malignant transformation of pleomorphic adenoma.

Establishment and characterization of pleomorphic adenoma cell systems: an in-vitro demonstration of carcinomas arising secondarily from adenomas in the salivary gland

Background

Among the salivary gland carcinomas, carcinoma in pleomorphic adenoma has been regarded as a representative carcinoma type which arises secondarily in the background of a pre-existent benign pleomorphic adenoma. It is still poorly understood how and which benign pleomorphic adenoma cells transform into its malignant form, carcinoma ex pleomorphic adenoma.

Methods

We have established five cell systems from a benign pleomorphic adenoma of the parotid gland of a 61-year-old woman. They were characterized by immunofluorescence, classical cytogenetics, p53 gene mutational analysis, fluorescence in-situ hybridization, and histopathological and immunohistochemical examinations of their xenografts, to demonstrate their potency of secondary transformation.

Results

We established and characterized five cell systems (designated as SM-AP1 to SM-AP5) from a benign pleomorphic adenoma of the parotid gland. SM-AP1 to SM-AP3 showed polygonal cell shapes while SM-AP4 and SM-AP5 were spindle-shaped. SM-AP1-3 cells were immunopositive for keratin only, indicating their duct-epithelial or squamous cell differentiation, while SM-AP4/5 cells were positive for both keratin and S-100 protein, indicating their myoepithelial cell differentiation. Chromosome analyses showed numeral abnormalities such as 5n ploidies and various kinds of structural abnormalities, such as deletions, translocations, derivatives and isodicentric chromosomes. Among them, der(9)t(9;13)(p13.3;q12.3) was shared by all five of the cell systems. In addition, they all had a common deletion of the last base G of codon 249 (AGG to AG_) of the p53 gene, which resulted in generation of its nonsense gene product. Transplanted cells in nude mice formed subcutaneous tumors, which had histological features of squamous cell carcinoma with apparent keratinizing tendencies. In addition, they had ductal arrangements or plasmacytoid appearances of tumor cells and myxoid or hyaline stromata, indicating some characteristics of pleomorphic adenoma.

Conclusion

This study demonstrates in vitro that certain cell types from pleomorphic adenoma are able to clone and survive over a long term and develop subcutaneous tumors in nude mice. The histological features of squamous cell carcinoma from the transplanted cell systems in nude mice might suggest a secondary onset of malignancy from a pre-existing benign adenoma.

Heterogeneous genetic profiles in soft tissue myoepitheliomas

Myoepithelioma, mixed tumor and parachordoma are uncommon soft tissue tumors thought to represent morphological variants of a single tumor type. The genetic basis of these neoplasms is poorly understood. However, they morphologically resemble mixed tumor of the salivary glands (also known as pleomorphic adenoma), a tumor characterized by deregulated expression of PLAG1 or HMGA2. To evaluate a possible genetic relationship between these soft tissue and salivary gland tumors, PLAG1 expression levels and the genomic status of PLAG1 and HMGA2 were investigated in five soft tissue myoepitheliomas and one pleomorphic adenoma. In addition, all tumors were cytogenetically investigated and whole genome DNA copy number imbalances were studied in five of them. The genetic profiles were heterogeneous and the only aberration common to all soft tissue myoepitheliomas was a minimally deleted region of 3.55 Mb in chromosome band 19p13. Recurrent deletion of CDKN2A suggests that inactivation of this tumor suppressor gene is pathogenetically important in a subset. Furthermore, PLAG1 rearrangement was found in a soft tissue tumor from a patient previously treated for a salivary pleomorphic adenoma, indicating either metastasis of the salivary gland lesion or that some soft tissue tumors develop through the same mechanisms as their salivary gland counterparts.

Mdm2, p53, p21 and pAKT protein pathways in benign neoplasms of the salivary gland

The p53 protein can be altered virtually in all human cancers. In the absence of p53 mutations, p53 inactivation is possible via complex formation with other proteins, such as Mdm2. Previous studies have shown an overexpression of Mdm2 and lack of p53 expression in pleomorphic adenomas. The pAkt protein is closely related to Mdm2, and has not been previously reported in salivary gland tumors. The aim of this study was to analyze the expression of Mdm2, p53, p21 and pAkt proteins in pleomorphic adenomas and myoepitheliomas by immunohistochemistry, Western blotting and immunofluorescence techniques. Overexpression of Mdm2 and pAkt was present in all the cell lines and tumors studied, whereas the expression of p53 and p21 proteins was considered absent. In conclusion, the signaling pathway in benign salivary gland neoplasm showed an important participation of Mdm2 overexpression protein in tumor formation, progression through inactivation of p53 action, or both, and of pAkt overexpression through increased translocation of Mdm2 protein to cellular nuclei.

Significance of P16INK4A hypermethylation gene in primary head/neck and colorectal tumors: it is a specific tissue event? Results of a 3-year GOIM (Gruppo Oncologico dell'Italia Meridionale) prospective study

BACKGROUND

Methylation of the p16 promoter is one of the most frequent mechanisms of gene inactivation; its incidence is extremely variable according to the type of tumor involved. Our purpose was to analyze the hypermethylation of the p16 promoter in laryngeal squamous cell carcinomas (LSCC), salivary gland (SG) tumors and in colorectal cancer (CRC), to detect any possible association with the clinicopathological features and to determine the prognostic significance of the p16 gene in the tumors analyzed.

PATIENTS AND METHODS

The hypermethylation of the p16 promoter was prospectively analyzed, by MSP, in a consecutive series of 64 locally advanced LSCC patients, in a consecutive series of 33 SG tumor patients and in a consecutive series of 66 sporadic CRC patients.

RESULTS

Hypermethylation was observed in 9% of the LSCC cases, in all cases of SG cancer and in 21% of the CRC cases. No significant association was observed between p16 hypermethylation and clinicopathological variables in all the tissue samples analyzed. Moreover at univariate analysis p16 mutations were not independently related at disease relapse and death in LSCC and CRC.

CONCLUSIONS

The results of this study suggest that the lack of p16 function could happen in advanced stage of SG tumors.

Cyclin D1 and p16 expression in pleomorphic adenoma and carcinoma ex pleomorphic adenoma of the parotid gland

AIMS

To compare cyclin D1 and p16(ink4) (p16) expression in normal tissue, pleomorphic adenoma (PA) and carcinoma ex pleomorphic adenoma (CXPA) of the parotid gland.

METHODS AND RESULTS

Immunohistochemistry was used to examine cyclin D1 and p16 expression in 43 parotid tumours (29 PAs and 14 CXPAs). Cyclin D1 and p16 were both significantly more likely to be expressed in the neoplastic than in the normal epithelial and stromal components of PA and CXPA (P < 0.001 and P < 0.005, respectively). Cyclin D1 was more likely to be expressed in the malignant components of CXPA than in the benign components of PA (50% versus 31% and 31%, respectively), but the trend was not statistically significant. There was no evidence of this association for p16 (corresponding positivity rates 69% versus 81% and 52%).

CONCLUSIONS

Our findings provide preliminary evidence of roles for cyclin D1 and p16 in the development of PA and for cyclin D1 in the progression of PA to CXPA.

TP53 and p16INK4A, but not H-KI-Ras, are involved in tumorigenesis and progression of pleomorphic adenomas

The putative role of TP53 and p16(INK4A) tumor suppressor genes and Ras oncogenes in the development and progression of salivary gland neoplasias was studied in 28 cases of pleomorphic adenomas (PA), 4 cases of cystic adenocarcinomas, and 1 case of carcinoma ex-PA. Genetic and epigenetic alterations in the above genes were analyzed by Polymerase Chain Reaction/Single Strand Conformational Polymorphism (PCR/SSCP) and sequencing and by Methylation Specific-PCR (MS-PCR). Mutations in TP53 were found in 14% (4/28) of PAs and in 60% (3/5) of carcinomas. Mutations in H-Ras and K-Ras were identified in 4% (1/28) and 7% (2/28) of PAs, respectively. Only 20% (1/5) of carcinomas screened displayed mutations in K-Ras. p16(INK4A) promoter hypermethylation was found in 14% (4/28) of PAs and 100% (5/5) carcinomas. All genetic and epigenetic alterations were detected exclusively in the epithelial and transitional tumor components, and were absent in the mesenchymal parts. Our analysis suggests that TP53 mutations and p16(INK4A) promoter methylation, but not alterations in the H-Ras and K-Ras genes, might be involved in the malignant progression of PA into carcinoma.

Loss of heterozygosity occurs predominantly, but not exclusively, in the epithelial compartment of pleomorphic adenoma

Pleomorphic adenoma (PA), being the most common benign tumor of the salivary glands, is composed of epithelial and mesenchymal compartments. In this study, we analyzed 19 microsatellite markers from chromosomal arms 6q, 8q, 9p, 12q, and 17p in 31 PAs and 3 carcinoma ex pleomorphic adenomas (CXPAs) as well as 11 other non-PA-related carcinomas of the salivary gland for comparison. In our analysis, we differentiated between epithelial and mesenchymal tissues. Loss of heterozygosity (LOH) in PAs was most often found in 8q (32%) and 12q (29%). Two of the three CXPAs displayed allelic loss at all chromosomal arms investigated, whereas the results of the non-PA-related carcinomas were rather heterogeneous. LOH could not only be detected in the epithelial, but also in the mesenchymal, compartments of a subset of PAs, especially at chromosomal arm 8q. Concerning the CXPAs, we were able to demonstrate allelic losses not only in the malignant epithelial compartment, but also in the residual adenoma parts. Our data give further evidence that alterations in 8q may be an early event in PA tumorigenesis, whereas LOH in 12q may characterize cells with the potential to transform in CXPAs.

Genetic and epigenetic alterations of 9p21 gene products in benign and malignant tumors of the head and neck

The multistep process of tumorigenesis has not been decoded to date, although numerous investigations into probable molecular changes have meanwhile been conducted. However, not only DNA changes or loss of alleles cause deregulation of gene function, but also epigenetic alterations (e.g. methylation) result in functional loss. The INK4a-ARF (CDKN2A) locus, located on chromosome 9p21, encodes two functionally distinct tumor suppressor genes, p14ARF and p16INK4a, which play active roles in the p53 and Rb tumor suppressive pathways. We therefore examined not only p16 and p14 proteins, but also alterations of the INK4a-ARF locus, including methylation and loss of heterozygosity in benign and malignant tumors of the head and neck (squamous cell carcinomas and pleomorphic adenomas). In benign pleomorphic adenomas, methylation of p14ARF was found in 1 out of 42 (2%) cases, whereas alterations of p16INK4a occurred in 12/42 (29%) pleomorphic adenomas. In HNSCC, methylation of p16INK4a occurred in 16 out of 50 (32%) carcinomas. P14ARF was found to be methylated in 8 out of 50 cases (16%). Our results demonstrate that alterations of the INK4a-ARF locus are frequent and important events not only in the carcinogenesis of malignant, but also in benign tumors.