First insights into the molecular basis of pleomorphic adenomas of the salivary glands

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.

A Comparative Review of Mixed Mammary Tumors in Mammals

Mixed tumors are characterized by the histological identification of two or more cell types. Commonly, a mixture of epithelial and myoepithelial cells is included in abundant stroma, which can consist of myxoid, chondroid or bony matrices. Spontaneously arising mixed tumors are rare lesions in the human breast but are common in human salivary glands and canine mammary glands. Subtle histopathological characteristics and overlapping attributes of malignant lesions with other benign lesions can lead to a diagnostic challenge. Mixed tumors can present as benign or malignant. While malignant mixed tumors are quite rare in the human breast they have a poor prognosis. Benign mixed mammary tumors occur more frequently in female dogs than in humans and are usually associated with a good prognosis. This review will provide a comprehensive overview of mixed mammary tumors, across various mammalian species.

Genomic copy number alterations of primary and secondary metastasizing pleomorphic adenomas

AIMS

Metastasizing pleomorphic adenoma (MPA) is a rare tumour, and its mechanism of metastasis still is unknown. To date, there has been no study on MPA genomics. We analysed primary and secondary MPAs with array comparative genomic hybridization to identify somatic copy number alterations and affected genes.

METHODS AND RESULTS

Tumour DNA samples from primary (parotid salivary gland) and secondary (scalp skin) MPAs were subjected to array comparative genomic hybridization investigation, and the data were analysed with NEXUS COPY NUMBER DISCOVERY. The primary MPA showed copy number losses affecting 3p22.2p14.3 and 19p13.3p123, and a complex pattern of four different deletions at chromosome 6. The 3p deletion encompassed several genes: CTNNB1, SETD2, BAP1, and PBRM1, among others. The secondary MPA showed a genomic profile similar to that of the primary MPA, with acquisition of additional copy number changes affecting 9p24.3p13.1 (loss), 19q11q13.43 (gain), and 22q11.1q13.33 (gain).

CONCLUSION

Our findings indicated a clonal origin of the secondary MPA, as both tumours shared a common profile of genomic copy number alterations. Furthermore, we were able to detect in the primary tumour a specific pattern of copy number alterations that could explain the metastasizing characteristic, whereas the secondary MPA showed a more unbalanced genome.

Myoepithelioma of the Orbital Apex and Middle Cranial Fossa: Case Report and Review of the Literature

Myoepitheliomas are rare tumours that originate from glandular tissues such as the parotid or salivary glands, and less commonly from soft tissues of the head, neck, and other parts of the body. Intraorbital myoepitheliomas generally arise from the lacrimal gland. Intracranial myoepitheliomas are rare. We report a myoepithelioma of the orbital apex that did not originate from the lacrimal gland. It extended to the middle cranial fossa from the orbital apex and involved the dura and adjacent bone. A diagnostic biopsy via a lateral orbitotomy preceded resection. We review the natural course and histopathology of myoepithelial neoplasms, the surgical nuances of approaching an orbital apex tumour with maximal functional preservation, and the optimal management practices of these rare lesions.

Canine mammary mixed tumours: a review

Mammary mixed tumours are the most frequent neoplasias in female dogs. In humans, mixed tumours are frequently found in the salivary glands and are known as pleomorphic adenomas. In addition to their histomorphologic similarities, mixed tumours and pleomorphic adenomas have the potential to become malignant and give rise to carcinomas in mixed tumours and carcinomas ex-pleomorphic adenoma, respectively. The factors associated with malignant transformation are still poorly known in the case of canine mixed tumours. However, this form of neoplasia tends to be associated with a better prognosis than other malignant histological types. This paper discusses the main features associated with female canine mammary mixed tumours.

PLAG1 alteration in carcinoma ex pleomorphic adenoma: immunohistochemical and fluorescence in situ hybridization studies of 22 cases

Carcinoma ex pleomorphic adenoma (CA-ex-PA) may arise with nearly any histologic subtype of carcinoma of the salivary gland. In the absence of recognizable residual pleomorphic adenoma (PA) or a prior history of PA, distinction of CA-ex-PA from morphologically similar de novo carcinomas may be difficult. Oncogenic rearrangement of PLAG1 (pleomorphic adenoma gene 1) has been established in PA; however, it has not yet been proven that PLAG1 alteration persists in carcinomas developed from preceding PA. We evaluated 22 histologically diverse CA-ex-PA by immunohistochemistry for PLAG1, and/or by FISH targeting PLAG1. Of these, 17 cases were immunoreactive (1+ to 3+) and 5 were immunonegative/rare positive for PLAG1. For comparison, 39 various salivary gland neoplasms were immunostained for PLAG1, of which all scored negative/rare positive. Twelve of 19 CA-ex-PA analyzed by PLAG1 FISH (63 %) were positive for gene rearrangement, 2 showed only a trisomy/polysomy profile, and 5 had a normal pattern. One FISH-positive tumor showed amplification of PLAG1. One of 3 cases analyzed for HMGA2 FISH was positive for gene rearrangement. In our series, the majority of CA-ex-PA harbored altered PLAG1 or HMGA2 genes detectable by FISH. While PLAG1 immunostain was specific for CA-ex-PA against other carcinomas, its application as a standalone discriminatory test was limited by variable expression. We conclude that most CA-ex-PA, regardless of morphologic subtype, carry altered PLAG1 or HMGA2 genes, and that FISH for PLAG1, along with immunohistochemistry for PLAG1, may help discriminate CA-ex-PA from its de novo carcinoma counterpart.

Disseminated carcinoma ex pleomorphic adenoma in an adolescent confirmed by application of PLAG1 immunohistochemistry and FISH for PLAG1 rearrangement

A 16-year-old previously asymptomatic boy presented with complaints of fatigue, weight loss, and back pain for several months. Imaging studies revealed a large superior mediastinal mass, numerous bilateral pulmonary nodules, and multiple lytic bone lesions. A needle biopsy from a sternal lesion showed a poorly differentiated carcinoma, immunoreactive for cytokeratins and EMA and immunonegative for various organ/tissue-specific markers.His past medical history was significant for excision of aparotid gland tumor 5 years earlier. Histologic review of the salivary gland tumor revealed a pleomorphic adenoma containing a microscopic focus of invasive carcinoma(carcinoma ex pleomorphic adenoma). By immunohistochemistry, both the salivary gland tumor and the disseminated carcinoma expressed PLAG1 with a strong nuclear pattern.Fluorescence in situ hybridization (FISH), using dual-color, break-apart probes for PLAG1, showed rearrangement of the gene in both the salivary gland and the disseminated tumors.FISH demonstrated additional cytogenetic aberrations in the carcinoma, including polysomy for chromosome 8 (in both the primary salivary gland and the metastatic tumors) and PLAG1 amplification (in the metastatic tumor). We conclude that in the proper clinicopathologic setting, application of PLAG1 immunohistochemistry and FISH for PLAG1 gene rearrangement may be valuable in establishing the diagnosis of carcinoma ex pleomorphic adenoma as the source of a cancer of unknown primary site.

Myeloid metaplasia in canine mixed mammary tumors: occurrence and characterization

BACKGROUND

Mixed tumors are among the most frequent mammary neoplasms in female dogs. Some of these tumors present bone marrow associated with the newly formed osseous tissue, characteristic of myeloid metaplasia.

OBJECTIVE

To evaluate the occurrence of these lesions in a series of mixed tumors, and determine its histomorphological characteristics.

ANIMALS AND METHODS

In total, 384 canine mammary mixed tumors from 289 animals have been reviewed. The lesions were classified according to the presence of osseous metaplasia associated with myeloid metaplasia or extramedullary hematopoiesis. Myeloid metaplasia characterization was determined from the morphological characteristics and organization of the cells and adjacent tissues. Cytoplasmic staining for CD31 and Factor VIII were used as a criterion to confirm the presence of blood vessels and megakaryocytes, respectively.

RESULTS

The 384 cases included 206 benign and 178 carcinomas in mixed tumors. Osseous metaplasia was present in 16.1% and calcified areas exclusively in 3.1% lesions. Among all osseous metaplasia, 33.9% presented some type of extramedullary hematopoiesis, of which 71.4% were classified as myeloid metaplasia and 28.6% as extramedullary hematopoiesis. Myeloid metaplasia cases consisted of 67% benign mixed tumors and 33% carcinomas in mixed tumors. CD31 and Factor VIII expression occurred in all myeloid metaplasia, confirming the presence of blood capillaries and megakaryocytes. Myeloid metaplasia was observed in 24% of mixed tumors containing osseous metaplasia and in 4% of all mixed tumors analyzed.

CONCLUSION

Despite the low frequency of this lesion, additional studies are needed to understand the implications of myeloid metaplasia in canine mammary mixed tumors.

A subset of cutaneous and soft tissue mixed tumors are genetically linked to their salivary gland counterpart

Neoplasms morphologically similar to mixed tumors and myoepitheliomas of the salivary glands, under the broad concept of myoepithelial neoplasia, have recently been defined in the skin and soft tissue; however, to date, no data have supported a shared genetic background with their salivary gland counterpart. From a large body of research, it has been well established that rearrangement of pleomorphic adenoma gene 1 (PLAG1) leads to aberrant expression of its protein and is pathogenically relevant in the development of salivary mixed tumors. On the other hand, in soft tissue lesions, compelling evidence suggests that EWSR1 is involved in a significant subset. To examine the hypothesis that there is a genetic link between these histologically similar tumors at different sites, we randomly selected 20 benign myoepitheliomas/mixed tumors of skin and soft tissue (10 cases each). Nineteen cases could be immunostained for PLAG1, of which 11 cases showed distinct nuclear staining with moderate or strong intensity in a significant number of cells. Interphase fluorescence in situ hybridization for PLAG1 was successfully performed in 11 cases (seven in skin and four in soft tissue) and was positive for gene rearrangement in eight cases (five in skin and three in soft tissue). All PLAG1-rearranged tumors, except one, had clear-cut ductal structures and were immunoreactive for PLAG1. In our series, tumors with PLAG1 alteration shared a common morphologic phenotype characterized by prominent tubuloductal differentiation, suggesting that myoepithelial neoplasms with genuine salivary gland-like morphology, so-called soft tissue/cutaneous mixed tumors, are genetically related to their salivary gland counterpart.

Pediatric epithelial salivary gland tumors: spectrum of histologies and cytogenetics at a children's hospital

There are conflicting reports regarding the relative frequency of benign and malignant epithelial salivary gland tumors in children. There are only a few reports of the cytogenetic abnormalities in the pleomorphic adenomas (PA) that arise in children, and even less information regarding the pleomorphic adenoma gene 1 (PLAG1) and high motility group A2 (HMGA2 ) histochemical staining in PAs, or their correlation with histologic types (stromal vs epithelial predominance). A retrospective 14 year review of epithelial salivary gland tumors encountered at a children's hospital identified 13 tumors: 12 PAs and 1 acinic cell carcinoma (ACC). No mucoepidermoid carcinomas were identified. Tumors arose in the parotid (7) and other sites (2 submandibular, 4 minor). Ten PAs in our cohort had cytogenetic studies. Four were normal, 5 involved 8q12, and 1 involved 12q13. Immunohistochemistry identified an additional 2 PAs with PLAG1 staining, and 5 additional PAs with HMGA2 staining. One tumor with ins(18;8)(q21.1;q12q22.2) had no PLAG1 staining, but stained with HMGA2. This ins(18;8) may not have involved the PLAG1 gene. There was no demonstrable correlation of 8q12/PLAG1 staining or 12q13/HMGA2 staining with histologic type. Thus we found abnormalities in either 8q12/PLAG1 staining or 12q13/HMGA2 staining in all PAs. The HMGA2 staining in 50% of PAs suggests that it may be more frequently involved in PAs than previously thought based on cytogenetic studies, at least in children.

The human pseudoxanthoma elasticum gene ABCC6 is transcriptionally regulated by PLAG family transcription factors

Mutations in the ABCC6 gene are known as causative factors of pseudoxanthoma elasticum (PXE), a connective tissue calcification disorder, but the molecular mechanism of pathogenesis or the physiological function of ABCC6 protein is the subject of intense debate. The ABCC6 gene expression is tightly regulated at the transcriptional level and its tissue-specific distribution is consistent with PXE being a metabolic disease caused by failure of ABCC6 function in organs distant from the diseased sites. In an effort to provide clues to its role by elucidating the mechanisms of its regulation, we identified ABCC6 as a target gene for transcriptional induction by PLAG1 and PLAGL1, transcription factors from the PLAG family of cell cycle progression-related DNA-binding proteins. Both these factors are shown to bind to the same single consensus-binding element in the ABCC6 proximal promoter in cell lines of hepatic and renal origin by reporter gene assay, electrophoretic mobility shift assay and chromatin immunoprecipitation. PLAG-mediated ABCC6 transactivation may play an important role in determining the level of tissue-specific expression of this gene. The described mechanism can also find potential application in therapeutic interventions in forms of PXE related to impaired ABCC6 expression.

Amplification of MGC2177, PLAG1, PSMC6P, and LYN in a malignant mixed tumor of salivary gland detected by cDNA microarray with tyramide signal amplification

Gene amplifications have been observed in many different tumor cells, and many of these changes are related to tumor pathogenesis. Comparative genomic hybridization (CGH) using metaphase chromosomes can detect changes in chromosome copy number with a resolution of 10-20 Mb. Current advances in CGH analysis in a microarray format allow us to refine such changes down to the gene level. We applied microarray technology to detect novel gene amplification in a malignant mixed tumor of salivary gland. Besides detecting previously known gene amplifications (MDM2 and MYC), we identified four other highly amplified genes located at 8q11.2 approximately q13: MGC2177, PLAG1, PSMC6P, and LYN. The amplification was further validated with real-time quantitative polymerase chain reaction.

Salivary-type neoplasms of the breast and lung

Salivary-type tumors occur in multiple sites in the human body, likely related to a basic structural homology between exocrine glands in these different anatomic areas. This paper reviews these salivary gland tumor types in breast tissue and lung. Salivary-type tumors of both breast and lung are relatively uncommon in comparison to their salivary gland counterparts. This may be attributable in part to lack of familiarity with these tumors in extra-salivary sites, and in part to histologic overlap with other primary and metastatic tumor types. Recognition of these entities is improving as the clinical and pathologic features are better delineated, and tumors are more accurately classified. Prediction of malignant behavior is not always possible in these unusual sites. In some instances, such as adenoid cystic carcinoma, behavior is known to differ considerably from that of analogous primary salivary gland tumors and in other instances there are simply too few reported cases to allow for adequate prognostication. In fact, more recent papers discuss the need to consider a spectrum encompassing benign and malignant lesions, in both breast and lung. Of course, some entities show clear-cut evidence of malignancy with documented potential for metastasis, others show bland features and well-reported benign behavior, and the less well-defined entities reside between these two extremes. The molecular pathology of salivary gland tumors has been reasonably well investigated in that location; however; there are few molecular studies devoted to salivary-type tumors of the breast and lung. This represents a potential area for future growth in further clarifying these tumors and their behavior.