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

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.

Pitfalls in Diagnosis of Myoepithelial Carcinoma of Salivary Glands: A Study of 3 Cases with Cytologic-histologic Correlation and Molecular Analysis

CONTEXT

Myoepithelial carcinoma (MECA) represents < 1% percent of salivary gland (SG) tumors with a mean age of 55 years. These tumors can arise de novo or in association with pre-existing pleomorphic Adenoma (PA). The cytologic features of MECA overlap with other SG neoplasms including the more common benign entities like PA and myoepithelioma and can pose a diagnostic challenge.

DESIGN

A database search for MECA was performed spanning 10 years. 3 cases qualified with available cyto-histologic correlation. All were morphologically MECA with one case diagnosed as MECA ex-PA. The cases were subjected to a comprehensive immunohistochemical and molecular evaluation (Case#1 has been previously reported and published in head and neck pathology in 2021).

RESULTS

A comparative analysis of these cases is presented in Table 1. All three cases were initially diagnosed as PA on cytology. On review of cytology slides, presence of metachromatic stromal fragments and bland myoepithelial cells was found to be the most common diagnostic pitfall. S100 was positive in all cases while myosin, p63, and GFAP were variably positive. Molecular analysis revealed novel, previously undescribed mutations in the three cases. Additionally, two of three cases expressed PD-L1, suggesting a role for immunotherapy in treatment.

CONCLUSIONS

Cytomorphology of MECA is poorly described in literature and can pose a diagnostic challenge due to overlapping features with salivary gland benign neoplasms. A conclusive diagnosis on cytology is often not possible. However, a high cellularity, predominant oncocytoid/ myoepithelial cell population on smears and cell block, along with a strong clinical and radiologic suspicion for malignant salivary gland tumor, should alert the cytopathologist and help avoid an erroneous benign diagnosis on cytology.

Distinct copy number signatures between residual benign and transformed areas of carcinoma ex pleomorphic adenoma

The mechanisms involved with the pathogenesis of carcinoma ex pleomorphic adenoma (CXPA) seem to be associated with the accumulation of molecular alterations in the pleomorphic adenoma (PA). In this sense, using array-based comparative genomic hybridization (aCGH) a rare series of 27 cases of CXPA and 14 residual PA (rPA) adjacent to the transformation area, we investigated the profile of the copy number alterations (CNAs) comparing benign residual and transformed areas. The main findings were correlated with the histopathological classification by histologic subtype and degree of invasion. The distribution of losses (p = 0.187) and amplifications (p = 0.172) was not statistically different between rPA and CXPA. The number of gains was increased in the transformed areas compared to the benign residual areas (p = 0.005). PLAG1 gain was maintained along the malignant transformation, as it was observed in both residual PA and CXPA samples, likely being an earlier event during transformation. The amplification of GRB7 and ERBB2 may also be an initial step in the malignant transformation of PA to CXPA (salivary duct carcinoma subtype). Furthermore, the amplification of HMGA2 and RPSAP52 were the most prevalent alterations among the studied samples. It was noteworthy that amplified genes in the transformed areas of the tumors were enriched for biological processes related to immune signaling. In conclusion, our results underscored for the first-time crucial CNAs in CXPA, some of them shared with the residual benign area adjacent to the transformation site. These CNAs included PLAG1 gain, as well as amplification of GRB7, ERBB2, HMGA2, and RPSAP52.

Proceedings of the 2024 North American Society of Head and Neck Pathology Companion Meeting, Baltimore, MD, March 24, 2024: Navigating Ancillary Studies in Basaloid/Blue Salivary Tumors

BACKGROUND

Basaloid salivary tumors can demonstrate significant morphologic overlap and be challenging to diagnose.

METHODS

A review of select ancillary studies in basaloid salivary tumors was performed.

RESULTS

A number of immunohistochemical stains, including PLAG1, HMGA2, β-catenin, MYB, and RAS Q61R, have been more recently incorporated into the diagnostic workup of basaloid salivary tumors.

CONCLUSIONS

Although reported variability in their performance has perhaps limited their widespread adoption, these immunohistochemical studies can nevertheless be useful in supporting pathologic diagnoses, particularly when considered in more specific differentials or when used as a panel with other markers.

Carcinoma Ex Pleomorphic Adenomas: An Institutional Experience and Literature Review

OBJECTIVES

To provide an institutional experience with cases diagnosed as carcinoma ex pleomorphic adenoma (CXPA), including the cytologic and histologic findings and clinical follow-up, followed by a comparison to the experience documented in the literature.

METHODS

We identified cases of CXPA diagnosed at our institution from 2011 to 2021 and reviewed the cytologic and histologic diagnoses, as well as the treatment and clinical outcomes. Additionally, a literature review of the English literature was performed on CXPAs from 2011 to 2021.

RESULTS

Forty-one cases of CXPA were identified, with the majority subclassified as adenocarcinoma, not otherwise specified. Five tumors underwent cytogenetic studies and five underwent molecular studies. To date, 36 patients are alive, 8 of whom experienced locoregional recurrence or distant metastasis.

CONCLUSIONS

Our institutional experience was comparable to that reported in the literature. Further studies are required to inquire about the role of molecular profiles of CXPAs in clinical risk assessment.

Myoepithelial carcinoma of the parotid gland with a novel CTCF::NCOA2 fusion

We describe a case of a myoepithelial carcinoma of the superficial parotid gland in a 46-year-old male harboring a novel CTCF::NCOA2 gene fusion. To our knowledge, this novel gene fusion has not been described previously in myoepithelial carcinoma. A 46-year-old male patient presented with a mass involving the superficial left parotid gland with extension into the external auditory canal (EAC) and erosion of the conchal cartilage. Histologically, the neoplasm was composed of uniform spindled, epithelioid/ovoid cells arranged in cords and nests within hyalinized to myxoid stroma. On immunohistochemistry (IHC), the tumor cells demonstrated patchy and variable staining for low molecular weight cytokeratin (CAM5.2), pan-cytokeratin (OSCAR), and S-100. Overall, the morphological and immunohistochemical attributes supported a locally aggressive tumor of myoepithelial differentiation consistent with myoepithelial carcinoma. Molecular analysis using a custom 115-gene gene panel by targeted RNA sequencing, showed an in-frame CTCF::NCOA2 fusion. In addition to reporting this novel fusion in myoepithelial carcinoma, we also discuss relevant differential diagnosis, and provide a brief review of NCOA2 gene function in both normal and neoplastic contexts.

Molecular testing of cytology specimens: overview of assay selection with focus on lung, salivary gland, and thyroid testing

Ancillary and molecular testing of cytopathology specimens has emerged as a reliable and useful tool to provide diagnostic information and treatment-related biomarker status for the management of cancer patients. The cytology specimens obtained through minimally invasive means have proven suitable testing substrates for a variety of ancillary tests, including immunohistochemistry, fluorescence in situ hybridization, as well as polymerase chain reaction and next generation sequencing molecular techniques. By focusing specifically on the cytology specimen, this review provides an overview of basic testing considerations and assay selection in addition to updates on the ancillary testing of cytologic tumor specimens from the lung, salivary gland, and thyroid.

Chromosome Translocations, Gene Fusions, and Their Molecular Consequences in Pleomorphic Salivary Gland Adenomas

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.

A molecular reappraisal of matrix-producing breast metaplastic carcinoma highlighted by PLAG1 and MYC rearrangements

Background:

Very little is currently known about molecular alteration of matrix-producing carcinoma of the breast. However, the morphological similarity with other neoplasm with a myxo-chondroid component is remarkable. In this pilot study we evaluated the molecular alterations involving PLAG1 and MYC genes in 12 cases of matrix producing carcinoma.

Methods:

We evaluated PLAG1 rearrangements as Break-Apart and Gene Copy Gain, and MYC as amplification and polysomy in 12 cases of matrix producing carcinoma using a FISH method.

Results:

Among the 12 cases of matrix producing carcinomas we found that the three cases harboring MYC amplification were all negative for PLAG1 break-apart; four cases with MYC polysomy were associated to PLAG1 break-apart and high Gene Copy Number; among four cases wild type for MYC, three showed a PLAG1- break-apart signal and of them two died with disease. One of the deceased patients showed an amplification of MYC with PLAG1- wild-type and the other showed a PLAG1 break-apart (6%) and a MYC wild-type.

Conclusion:

This is the first report to the best of our knowledge that shows a possible correlation between a matrix producing carcinoma with PLAG1 and MYC involvement in the development and progression of this kind of tumor. We can suppose that MYC amplification behaves in an aggressive way together with PLAG1- break-apart in the cases of matrix producing carcinoma presented here. The gene copy gain is a useful diagnostic tool in the case of difficult diagnosis because an increase was observed in more than 50% of cases.

Myoepithelial Carcinoma Ex-Pleomorphic Adenoma: A Rare Pathology Misdiagnosed as Pleomorphic Adenoma; With a Novel TERT Promoter Mutation and High PD-L1 Expression

Myoepithelial carcinoma (MECA) is a rare salivary gland (SG) neoplasm (0.1-0.45% of all SG tumors) that often presents with bland cytomorphology and can be misclassified as cellular pleomorphic adenoma (PA) or myoepithelioma. This is particularly challenging in MECA ex-PA cases, especially if tumor shows minimal to no capsular invasion. We report a rare case of a 76-year-old female; history of left superficial parotidectomy with diagnosis (outside hospital) of cellular PA, who re-presented 9 months post surgery with enlarging left parotid mass, neck lymphadenopathy and facial nerve deficits. FNAB of parotid and neck lymph node revealed cellular aspirates with loosely cohesive clusters of myoepithelial cells with occasional chondromyxoid stroma. Prior resection slides were reviewed, and diagnosis of MECA ex-PA was made. Patient underwent left radical parotidectomy, selective neck dissection, with facial nerve sacrifice (due to extensive encasing by tumor). Histology showed a multinodular tumor with pushing borders, zonal arrangement comprising of a hypocellular, necrotic/myxoid center, and a peripheral rim of myoepithelial cells, confirmed by positive S100, and p63. Tumor extensively infiltrated peri parotid soft tissues with multiple foci of lymphovascular and perineural invasion; and metastatic neck lymph nodes. Next generation sequencing revealed a novel TERT promoter mutation (c.-124C > T), not usually described in SG neoplasms. Further, PD-L1 immunohistochemistry showed positive expression, making patient eligible for anti-PDL-1 immunotherapy. This case highlights importance of recognizing the subtle malignant features of MECA in distinguishing it from benign mimics like PA. In addition, presence of TERT mutation opens a new arena for future research to explore potential treatment targets.

HMGA2 Immunoexpression is frequent in salivary gland pleomorphic adenoma: immunohistochemical and molecular analyses of PLAG1 and HMGA2 in 25 cases

The main oncologic events in pleomorphic adenoma (PA) are the translocations of Pleomorphic adenoma gene 1 (PLAG1) on chromosome 8q12 and High-mobility group AT-hook 2 (HMGA2) on chromosome 12q14.3 with various fusion partners. These translocations result in the transcriptional up-regulation of PLAG1 and HMGA2 proteins. We carried out a preliminary evaluation of PLAG1 translocation by fluorescence in-situ hybridization (FISH), immunohistochemistry (IHC) and HMGA2 IHC on twenty-five archived formalin-fixed paraffin-embedded tissues of PAs and its clinicopathologic features. Only eight cases were successfully hybridized and 50% of the interpretable cases were considered positive for PLAG1 translocation. PLAG1 IHC was only positive in 2 (8%) of the 25 cases stained, including one of the positive PLAG1 translocation cases. HMGA2 IHC was positive in 12 (48%) of the 25 cases stained including 2 (50%) of the 4 cases identified with PLAG1 translocation by FISH, 3 (75%) of the 4 cases negative for PLAG1 translocation by FISH and 7 (41%) of the 17 cases with failed hybridization. Overall, 15 (60%) of the 25 PA cases demonstrated PLAG1 and/or HMGA2 alterations confirmed either by FISH or IHC. In conclusion, PLAG1 and HMGA2 alterations were confirmed either by FISH or IHC in this cohort and HMGA2 alteration is a common event in PAs of salivary gland.

Fusion-Positive Salivary Gland Carcinomas

Salivary gland tumors are a rare, heterogeneous group of neoplasms that pose significant diagnostic challenges for the histopathologist. Histopathological diagnosis relies primarily on morphological assessment, with ancillary special stains and immunohistochemistry. In recent years, new defining genomic alterations have been characterized in these tumors. In particular, they include gene fusions which have shown to be tightly tumor-type specific, and thus valuable for use in diagnostically challenging cases. These discoveries also help in refining tumor classification. Furthermore, such genetic alterations may have prognostic as well as potentially therapeutic implications in the era of personalized medicine. This review aims at providing a summary of the most recent updates in this field.

Intraductal carcinoma of the salivary gland with NCOA4-RET: expanding the morphologic spectrum and an algorithmic diagnostic approach

After the publication of the 2017 World Health Organization Classification of Head and Neck Tumours, there has been increasing interest in the classification of newly categorized intraductal carcinomas. Intraductal carcinoma (IC) is an indolent tumor, typically arising in the parotid gland, with an intact myoepithelial layer and a cystic, papillary, often cribriform architecture. Early studies of IC identified a heterogeneous group of molecular alterations driving neoplasia, and recent studies have defined three primary morphological/immunohistochemical variants, subsequently linking these morphologic variants with defined molecular signatures. Although studies to date have pointed toward distinct molecular alterations after histological classification, this study used a novel approach, focusing primarily on six cases of IC with NCOA4-RET gene rearrangement as determined by next-generation sequencing and describing the spectrum of clinicopathologic findings within that molecularly-defined group, among them a unique association between the NCOA4-RET fusion and hybrid variant IC and the first case of IC arising in association with a pleomorphic adenoma. RET-rearranged IC show histological and immunohistochemical overlap with the more widely recognized secretory carcinoma, including low-grade morphology, a lumen-forming or microcystic growth pattern, and co-expression of S100, SOX10, and mammaglobin, findings undoubtedly leading to misdiagnosis. Typically regarded to have ETV6-NTRK3 fusions, secretory carcinomas may alternatively arise with RET fusions as well. Adding our cohort of six NCOA4-RET fusion-positive IC compared with four cases of secretory carcinoma with ETV6-RET fusions and a single case of fusion-negative IC with salivary duct carcinoma-like genetics, we propose a diagnostic algorithm that integrates histological elements, including atypia and invasiveness, and the likelihood of specific molecular alterations to increase diagnostic accuracy in what can be a very subtle diagnosis with important clinical implications.

Targeted RNA sequencing in the routine clinical detection of fusion genes in salivary gland tumors

Salivary gland tumors represent a diverse group of neoplasms that occasionally pose a diagnostic challenge for pathologists, particularly with limited sampling. Gene fusions, which may reflect genetic drivers, are increasingly recognized in a subset of these neoplasms, and can be leveraged for diagnostic purposes. We performed a retrospective analysis on a cohort of 80 benign and malignant salivary gland tumors, enriched for subtypes known to harbor recurrent fusion events, to validate the diagnostic use of a targeted RNA sequencing assay to detect fusion transcripts. Testing identified fusion genes in 71% (24/34) of pleomorphic adenoma and carcinoma-ex-pleomorphic adenoma, with 56% of cases showing rearrangement of PLAG1 and 15% HMGA2. In addition to confirming known partners for these genes, novel PLAG1 fusion partners were identified, including DSTN, NTF3, and MEG3; CNOT2 was identified as a novel fusion partner for HMGA2. In adenoid cystic carcinoma, 95% of cases (19/20) were positive for a fusion event. MYB was rearranged in 60% (12/20), MYBL1 in 30% (6/20), and NFIB in 5% (1/20); two tumors exhibited novel fusion products, including NFIB-TBPL1 and MYBL1-VCPIP1. Fusion genes were identified in 64% (9/14) of cases of mucoepidermoid carcinoma; MAML2 was confirmed to partner with either CRTC1 (43%) or CRTC3 (21%). One salivary duct carcinoma was found to harbor a novel RAPGEF6-ACSL6 fusion gene. Finally, as anticipated, gene fusions were not detected in any of the five acinic cell carcinomas included in the cohort. In summary, targeted RNA sequencing represents a diagnostically useful ancillary technique for identifying a variety of existing, and novel, fusion transcripts in the classification of salivary gland neoplasms.

Molecular Pathology of Salivary Gland Neoplasms: Diagnostic, Prognostic, and Predictive Perspective

Salivary gland neoplasms are an uncommon and widely heterogeneous group of tumors. In recent years, there has been considerable progress in efforts to reveal the molecular landscape of these tumors, although it is still limited and appears to be only the tip of the iceberg. Genomic aberrations, especially specific chromosomal rearrangements including CRTC1-MAML2 and CRTC3-MAML2 in mucoepidermoid carcinoma, MYB-NFIB and MYBL1-NFIB fusions in adenoid cystic carcinoma, PLAG1 and HMGA2 alterations in pleomorphic adenoma and carcinoma ex pleomorphic adenoma, ETV6-NTRK3 and ETV6-RET in secretory carcinoma, EWSR1-ATF1 and EWSR1-CREM in clear cell carcinoma, provide new insights into the molecular pathogenesis of various salivary gland neoplasms and help to better classify them. These genetic aberrations primarily serve as diagnostic tools in salivary gland tumor diagnosis; however, some also have promise as prognostic or predictive biomarkers. This review summarizes the latest developments in molecular pathology of salivary gland tumors with a focus on distinctive molecular characteristics.

Myoepithelial Carcinoma

Myoepithelial carcinoma (MECA) may overlap histologically with other salivary gland neoplasms, especially pleomorphic adenoma. MECA is characterized by cellular, uniform growth of myoepithelial cells and multinodular expansile invasive pattern with zonal cellular distribution. It may arise de novo or in association with pleomorphic adenoma (myoepithelial carcinoma ex pleomorphic adenoma). By immunohistochemistry, MECA is positive for cytokeratins and at least one of the myoepithelial markers, including S100. PLAG1 fusion is the most common genetic alteration. Carcinoma ex pleomorphic adenoma and necrosis correlate with worse clinical outcome in MECA, and necrosis can be used to stratify MECA as high grade.

Recent advances in smooth muscle tumors with PGR and PLAG1 gene fusions and myofibroblastic uterine neoplasms

Uterine epithelioid and myxoid leiomyosarcomas and inflammatory myofibroblastic tumors are rare mesenchymal neoplasms. Next-generation sequencing recently detected novel PGR fusions in uterine epithelioid leiomyosarcomas that demonstrate characteristic rhabdoid and spindled morphology. PLAG1 gene fusions have also been identified in a subset of myxoid leiomyosarcomas and are associated with PLAG1 overexpression. ALK rearrangements underpin the vast majority of uterine inflammatory myofibroblastic tumors, which demonstrate morphologic, and immunohistochemical features similar to those of inflammatory myofibroblastic tumors elsewhere. This review summarizes the morphologic, immunophenotypic, and molecular genetic features of PGR fusion-positive epithelioid leiomyosarcoma, PLAG1 fusion-positive myxoid leiomyosarcoma, and inflammatory myofibroblastic tumors of the uterus.

Increased ERBB2 Gene Copy Numbers Reveal a Subset of Salivary Duct Carcinomas with High Densities of Tumor Infiltrating Lymphocytes and PD-L1 Expression

Salivary duct carcinoma (SDC) commonly expresses androgen receptor (AR) and HER2, giving rise to treatment implications. SDC may also express programmed-death-ligand-1 (PD-L1), a predictive marker of response to checkpoint inhibitors. PD-L1 can be associated with genomic instability and high density of tumor infiltrating lymphocytes (TILs). Evaluation of HER2 immunohistochemistry (IHC) in SDC is not standardized, and relationships between ERBB2 copy numbers, PD-L1 expression and TILs in SDC are unknown. We evaluated 32 SDCs for HER2, AR and PD-L1 expression (IHC), ERBB2 status (FISH) and TILs (slide review). HER2 was scored with three different systems (breast, gastric, proposed salivary gland). PD-L1 was evaluated with the combined positive score. Most patients were older men, presenting at advanced clinical stage with nodal or distant metastases. During follow-up (mean 5 years, range 6 months to 21 years), 25 of the 32 patients (78%) died of SDC. We propose a HER2 IHC scoring system which accurately predicts underlying ERBB2 amplification or increased copy numbers in SDC. Most tumors had increased ERBB2 copy numbers (19/32 amplification, 6/32 aneusomy), a finding associated with higher TIL densities (p = 0.045) and PD-L1 expression (p = 0.025). Patients with TILs ≥ 40% had better prognoses (Log-Rank p = 0.013), with TILs being favorable prognosticators in univariate analysis (Hazard ratio: 0.18, p = 0.024). A subset of SDCs with increased ERBB2 copy numbers have higher TILs and PD-L1 expression. TILs ≥ 40% are associated with better prognosis.

Giant Cell Carcinosarcoma of the Parotid Gland With a PLAG 1 Translocation in Association With a Pleomorphic Adenoma With HMGA2 Translocation

OBJECTIVES

Carcinosarcomas of the salivary gland are rare neoplasms and have been described arising de novo or in association with pleomorphic adenoma (PA). PLAG1 and HMGA2 translocations are known to occur in PAs and carcinomas ex PA but are mutually exclusive.

METHODS

We report a case of a carcinosarcoma in the parotid gland of a 77-year-old man with unusual anaplastic sarcomatoid giant cell morphology.

RESULTS

Microscopically, a small separate PA was found adjacent to the carcinosarcoma. By conventional notion, the PA and carcinosarcoma would be considered related, as carcinosarcomas are well known to arise from PAs (carcinosarcoma ex PA). However, fluorescence in situ hybridization (FISH) assay demonstrated PLAG1 translocation in the carcinosarcoma and HMGA2 translocation in the separate PA.

CONCLUSIONS

These findings support that the carcinosarcoma likely originated from another PA with a PLAG1 translocation or de novo but not from the coexisting PA harboring a different translocation. To our knowledge, the case is the first to demonstrate PLAG1 translocation by FISH in a sarcomatous component of any parotid gland tumor, which may help better classify these tumors. In addition, multiple PAs are commonly found in the salivary gland, and to our knowledge, our case is the first to demonstrate that the same parotid gland can host PAs and PA-related tumors with different translocations.

Myoepithelioma of soft tissue and bone, and myoepithelioma-like tumors of the vulvar region: Clinicopathological study of 15 cases by PLAG1 immunohistochemistry

We demonstrated the clinicopathological findings of 13 myoepitheliomas of soft tissue and bone (MESTBs) and two myoepithelioma-like tumors of the vulvar region (MELTVRs), focusing on the association between nuclear atypia and clinical course, and the utility of immunohistochemistry (IHC) of pleomorphic adenoma gene 1 (PLAG1) for the pathological diagnosis of these tumors. Of the 13 MESTBs, eight, one and four cases exhibited mild, moderate and severe nuclear atypia, respectively. Two cases with venous invasion showed severe nuclear atypia and both died of advanced disease. Two MELTVR cases showed moderate nuclear atypia and had no evidence of disease after surgery. On IHC, 12 of 13 (92.3%) MESTBs showed PLAG1 immunoreactivity and none of the MELTVRs expressed PLAG1. In addition, MELTVRs showed loss of INI1 expression. In contrast, all MESTBs retained INI1 expression. Fluorescence in situ hybridization detected EWSR1, FUS and PLAG1 rearrangement in 5 (38.5%), 0 (0%) and 2 (15.4%) of the 13 MESTBs, respectively. No EWSR1, FUS and PLAG1 rearrangement were observed in the METLVRs. In conclusion, MESTBs with both severe nuclear atypia and venous invasion would be indicative of malignant potential. PLAG1 might be a useful IHC marker in MESTB diagnosis.

Misinterpreted Myoepithelial Carcinoma of Salivary Gland: A Challenging and Potentially Significant Pitfall

Myoepithelial carcinoma (MECA) is an underrecognized challenging entity with a broad morphologic spectrum. Misinterpreting MECA is not uncommon as distinguishing it from its mimics, especially cellular myoepithelial-rich pleomorphic adenoma (PA), can be difficult. We described 21 histologically challenging cases of MECAs (16 MECA ex-PA and 5 MECA de novo). All MECAs ex-PA were intracapsular or minimally invasive except for 3 cases. Eighteen (86%) were initially misinterpreted as benign neoplasms, including PA (10), atypical PA (5), and myoepithelioma (3). The remaining 3 were initially diagnosed as malignant (MECA ex-PA) but were histologically challenging. Histologic features that were found most helpful in recognizing the malignant nature of MECA included: uniformly cellular myoepithelial proliferation with an expansile nodular lobulated pattern (all cases) and alternate hypocellular and hypercellular zonal distribution (76% of cases). Among the 16 MECA patients with follow-up, 14 (87.5%) progressed: 10 developed local recurrence and 5 distant metastases. In contrast, only one of 33 patients with cellular PA (control group) recurred locally. Ten of the 14 MECAs that progressed were MECA ex-PA, and 12 (85%) had an initial benign diagnosis. Two patients with MECA ex-PA died of their disease; one had an initial diagnosis of PA. MECA is a histologically challenging entity that closely mimics PA and seems to carry a significant risk of recurrence. Areas of clonal appearing cellular myoepithelial growth with an expansile nodular lobulated pattern and zonal cellular distribution distinguish the majority of MECAs and may serve as useful diagnostic histologic features to differentiate MECA from its benign mimics.

Soft Tissue Special Issue: Myoepithelial Neoplasms of Soft Tissue: An Updated Review with Emphasis on Diagnostic Considerations in the Head and Neck

Primary myoepithelial neoplasms of soft tissue have been shown to be related to their salivary gland counterparts, with which they often share morphologic, immunophenotypic, and molecular genetic features, such as the presence of PLAG1 rearrangement in both soft tissue mixed tumor and salivary pleomorphic adenoma. However, important distinctions remain between soft tissue and salivary myoepithelial neoplasms, namely differing criteria for malignancy. This review provides an overview of the current understanding of the clinicopathologic and molecular features of soft tissue myoepithelial neoplasms, including discussion of the similarities and differences between soft tissue and salivary counterparts and relevant diagnostic issues specific to head and neck pathology practice.

Novel PLAG1 Gene Rearrangement Distinguishes a Subset of Uterine Myxoid Leiomyosarcoma From Other Uterine Myxoid Mesenchymal Tumors

Genetic alterations in uterine myxoid leiomyosarcoma are unknown. We investigate the clinicopathologic features of 19 uterine tumors previously diagnosed as myxoid leiomyosarcomas in which tumoral RNA was subjected to targeted RNA sequencing. PLAG1, BCOR, BCORL1, HMGA2, and ALK break-apart fluorescence in situ hybridization (FISH) and BCOR, PLAG1, and ALK immunohistochemistry were performed in cases which failed or lacked fusions by sequencing. The diagnosis of myxoid leiomyosarcoma was confirmed in 15 cases after exclusion of 4 tumors with BCOR and ALK rearrangements. These 15 patients presented at a median age of 50 years with stage I (3), II (2), III (2), and IV (1) tumors, respectively; stage was unknown in 7 cases. Tumor size ranged from 10 to 24 cm. Matrix was myxoid in all tumors and also eosinophilic in 2. Cells were spindled, epithelioid, and both in 10, 2, and 3 tumors and showed mild, moderate, and severe nuclear atypia in 3, 8, and 4 tumors, respectively. Mitotic index ranged from <1 to 14/10 HPF, while tumor necrosis was present in 6 (40%). Novel TRPS1-PLAG1 or RAD51B-PLAG1 fusions were detected by sequencing in 4 tumors, 3 of which were also confirmed by FISH. Diffuse PLAG1 expression was seen in 7 tumors, including 4 with PLAG1 rearrangement. No morphologic differences were seen among PLAG1 fusion-positive and fusion-negative tumors. No PLAG1, HMGA2, ALK, BCOR, or BCORL1 rearrangements were detected by FISH in 11 tumors. On the basis of sequencing and FISH results, PLAG1 rearrangements resulting in PLAG1 expression underpin ~25% of myxoid leiomyosarcomas and may serve as a useful diagnostic biomarker. Immunohistochemistry, targeted RNA sequencing, and/or FISH may distinguish myxoid leiomyosarcoma from its morphologic mimics.

Ancillary testing in salivary gland cytology: A practical guide

Salivary gland cytology is challenging, and historically the role of ancillary testing has been limited. However, numerous molecular/genetic advances in the understanding of salivary gland neoplasms during the last decade have facilitated the development of many useful diagnostic markers, such as PLAG1 and HMGA2 immunohistochemistry for pleomorphic adenoma and ETV6 fluorescence in situ hybridization for secretory carcinoma. Numerous salivary gland neoplasms are characterized by specific molecular/genetic alterations, many of which can be identified on cytologic preparations by karyotype analysis, fluorescence in situ hybridization, or immunohistochemical surrogates. Next-generation sequencing also has potential diagnostic applications, although to the authors' knowledge it currently has no routine role in salivary cytology. The primary goal of salivary fine-needle aspiration (FNA) is to facilitate appropriate clinical management. Ancillary testing has greatly enhanced the ability for accurate classification as per The Milan System for Reporting Salivary Gland Cytopathology and allows for the definitive diagnosis of many salivary FNA specimens, and also may resolve diagnostic uncertainty for FNAs that may be classified in The Milan System for Reporting Salivary Gland Cytopathology categories of salivary gland neoplasm of uncertain malignant potential or suspicious for malignancy. This review provides an updated discussion of the molecular/genetic features of the more commonly encountered salivary neoplasms by FNA, and discusses the application of available diagnostic immunohistochemical and molecular tests in salivary gland cytology.

Different correlations between tumor size and cancer-related gene profiles according to histologic type of salivary gland tumor

Salivary gland tumors are mostly benign, and malignant tumors are rare. Because of this rarity, there is little molecular biology research on salivary gland tumors. Recently, we have published an analysis of the telomere length (TL) in salivary gland tumors. In this paper, we analyzed amplification of the catalytic subunit of phosphatidylinositol 3-kinase (PIK3CA) and mitochondrial DNA copy number (mtCN) in salivary gland tumors. To investigate mutations in PIK3CA, we performed genomic sequencing on samples of salivary gland tumors extracted from patients. The expression level of PIK3CA mRNA and mtCN were measured by RT-PCR. PIK3CA amplification and mtCN did not differ between Warthin's tumor (WT), pleomorphic adenoma (PA), and carcinoma of the salivary gland. The size of the tumor and the molecular profile correlated in three relationships: the size of WT with PIK3CA and with mtCN, and the size of PA with TL. We found no correlation between the size of carcinoma and the molecular profile. There was no correlation between age and molecular profile in all histologic groups of salivary gland tumor. We found no correlation between TL and mtCN in each histologic group. Although we have not found any significant results for the molecular profile of salivary gland tumors, our study can be a basis for further studies on other oncogenes in salivary gland tumors.

The Role of Ancillary Techniques in Salivary Gland Cytopathology Specimens

Salivary gland tumor aspiration cytology is a useful preoperative test to guide the most appropriate clinical and surgical management for these patients. Although salivary gland cytology is often useful to distinguish between non-neoplastic lesions, benign neoplasms and malignant neoplasms, there remain many challenges in this area. Specifically, these tumors are uncommon and may have considerable morphologic overlap, especially in the setting of a malignant tumor. This article reviews some of the immunohistochemical and molecular characteristics of more common salivary gland neoplasms that pathologists and cytotechnologists may encounter. When used in combination with morphologic features, such ancillary testing can be useful to further refine the differential diagnosis, more strongly favor a particular entity, or in some instances confidently provide a specific diagnosis.

The Role of Molecular Testing in the Differential Diagnosis of Salivary Gland Carcinomas

Salivary gland neoplasms are a morphologically heterogenous group of lesions that are often diagnostically challenging. In recent years, considerable progress in salivary gland taxonomy has been reached by the discovery of tumor type-specific fusion oncogenes generated by chromosome translocations. This review describes the clinicopathologic features of a selected group of salivary gland carcinomas with a focus on their distinctive genomic characteristics. Mammary analog secretory carcinoma is a recently described entity characterized by a t(12;15)(p13;q25) translocation resulting in an ETV6-NTRK3 fusion. Hyalinizing clear cell carcinoma is a low-grade tumor with infrequent nodal and distant metastasis, recently shown to harbor an EWSR1-ATF1 gene fusion. The CRTC1-MAML2 fusion gene resulting from a t(11;19)(q21;p13) translocation, is now known to be a feature of both low-grade and high-grade mucoepidermoid carcinomas associated with improved survival. A t(6;9)(q22-23;p23-34) translocation resulting in a MYB-NFIB gene fusion has been identified in the majority of adenoid cystic carcinomas. Polymorphous (low-grade) adenocarcinoma and cribriform adenocarcinoma of (minor) salivary gland origin are related entities with partly differing clinicopathologic and genomic profiles; they are the subject of an ongoing taxonomic debate. Polymorphous (low-grade) adenocarcinomas are characterized by hot spot point E710D mutations in the PRKD1 gene, whereas cribriform adenocarcinoma of (minor) salivary glands origin are characterized by translocations involving the PRKD1-3 genes. Salivary duct carcinoma (SDC) is a high-grade adenocarcinoma with morphologic and molecular features akin to invasive ductal carcinoma of the breast, including HER2 gene amplification, mutations of TP53, PIK3CA, and HRAS and loss or mutation of PTEN. Notably, a recurrent NCOA4-RET fusion has also been found in SDC. A subset of SDC with apocrine morphology is associated with overexpression of androgen receptors. As these genetic aberrations are recurrent they serve as powerful diagnostic tools in salivary gland tumor diagnosis, and therefore also in refinement of salivary gland cancer classification. Moreover, they are promising as prognostic biomarkers and targets of therapy.

Primary Myoepithelial Carcinoma of the Conjunctiva

A 38-year-old female, otherwise fit and well, presented with a mass on her left medial bulbar conjunctiva that had been enlarging for several months. Examinations showed a fixed pinkish tumour, 9 mm in maximum extent, spanning from the plica to the medial limbus. The tumour was removed in toto. Histology revealed it to be a biphasic tumour composed of lobules and infiltrative cords within a sclerotic matrix. The cells were spindle-shaped to epithelioid, with nuclear atypia and occasional mitotic figures. The tumour was positive for smooth muscle actin, beta-catenin, and vimentin. All other markers of myoepithelial differentiation and cytokeratins were negative. Genetic analysis showed no evidence of EWSR1 or PLAG1 rearrangements. The light microscopic features and immunohistochemistry strongly supported a tumour with myoepithelial differentiation. The cellular atypia, mitotic activity, and infiltrative edges all pointed to myoepithelial carcinoma. Body imaging/screening showed no evidence of tumour elsewhere, supporting that the tumour was a primary of the conjunctiva. This is the first report of a myoepithelial tumour of the conjunctiva. The patient remains recurrence-free after 3 years of follow-up.

Clinicopathological effect of PLAG1 fusion genes in pleomorphic adenoma and carcinoma ex pleomorphic adenoma with special emphasis on histological features

AIMS

Pleomorphic adenoma gene 1 (PLAG1) rearrangement is well known in pleomorphic adenoma (PA), which is histologically characterised by admixed epithelial and mesenchymal components. Multiple fusion variants of PLAG1 and HMGA2 have been reported; currently, however, little is known regarding the clinicopathological impacts of these fusion types METHODS AND RESULTS: We examined the PLAG1- and HMGA2-related fusion status in 105 PAs and 11 cases of carcinoma ex PAs (CXPA) arising from salivary glands and lacrimal glands to elucidate their correlation to the clinicopathological factors. Forty cases harboured PLAG1 fusion genes: CTNNB1-PLAG1 in 22 cases, CHCHD7-PLAG1 in 14 cases and LIFR-PLAG1 in four cases. Only two cases possessed HMGA2 fusion genes. The mean age of LIFR-PLAG1-positive cases was significantly higher than that of CTNNB1-PLAG1- and CHCHD7-PLAG1-positive cases (P = 0.0358). PAs located in the submandibular gland demonstrated CTNNB1-PLAG1 fusion at a significantly higher rate than other fusions (P = 0.0109). Histologically, PLAG1 fusion-positive cases exhibited chondroid formation and plasmacytoid features more commonly (P = 0.043, P = 0.015, respectively) and myxoid abundant feature less frequently (P = 0.031) than PLAG1 fusion-negative cases. For CXPAs, four CTNNB1-PLAG1 fusions were detected in two salivary duct carcinomas and two myoepithelial carcinomas. Ductal formation was observed frequently (90.9%) in residual PA.

CONCLUSIONS

The presence of PLAG1 fusion was associated with specific histological features in PA. Detecting the PLAG1 fusion gene and searching residual ductal formation in salivary gland malignant tumours with extensive hyalinisation could be useful for diagnosis.

Clinical Utility of In Situ Hybridization Assays in Head and Neck Neoplasms

Head and neck pathology present a unique set of challenges including the morphological diversity of the neoplasms and presentation of metastases of unknown primary origin. The detection of human papillomavirus and Epstein-Barr virus associated with squamous cell carcinoma and newer entities like HPV-related carcinoma with adenoid cystic like features have critical prognostic and management implications. In salivary gland neoplasms, differential diagnoses can be broad and include non-neoplastic conditions as well as benign and malignant neoplasms. The detection of specific gene rearrangements can be immensely helpful in reaching the diagnosis in pleomorphic adenoma, mucoepidermoid carcinoma, secretory carcinoma, hyalinizing clear cell carcinoma and adenoid cystic carcinoma. Furthermore, molecular techniques are essential in diagnosis of small round blue cell neoplasms and spindle cell neoplasms including Ewing sarcoma, rhabdomyosarcoma, synovial sarcoma, biphenotypic sinonasal sarcoma, dermatofibrosarcoma protuberans, nodular fasciitis and inflammatory myofibroblastic tumor. The detection of genetic rearrangements is also important in lymphomas particularly in identifying 'double-hit' and 'triple-hit' lymphomas in diffuse large B cell lymphoma. This article reviews the use of in situ hybridization in the diagnosis of these neoplasms.

PLAG1, SOX10, and Myb Expression in Benign and Malignant Salivary Gland Neoplasms

Background

Recent findings in molecular pathology suggest that genetic translocation and/or overexpression of oncoproteins is important in salivary gland tumorigenesis and diagnosis. We investigated PLAG1, SOX10, and Myb protein expression in various salivary gland neoplasm tissues.

Methods

A total of 113 cases of surgically resected salivary gland neoplasms at the National Cancer Center from January 2007 to March 2017 were identified. Immunohistochemical staining of PLAG1, SOX10, and Myb in tissue samples was performed using tissue microarrays.

Results

Among the 113 cases, 82 (72.6%) were benign and 31 (27.4%) were malignant. PLAG1 showed nuclear staining and normal parotid gland was not stained. Among 48 cases of pleomorphic adenoma, 29 (60.4%) were positive for PLAG1. All other benign and malignant salivary gland neoplasms were PLAG1-negative. SOX10 showed nuclear staining. In normal salivary gland tissues SOX10 was expressed in cells of acinus and intercalated ducts. In benign tumors, SOX10 expression was observed in all pleomorphic adenoma (48/48), and basal cell adenoma (3/3), but not in other benign tumors. SOX10 positivity was observed in nine of 31 (29.0%) malignant tumors. Myb showed nuclear staining but was not detected in normal parotid glands. Four of 31 (12.9%) malignant tumors showed Myb positivity: three adenoid cystic carcinomas (AdCC) and one myoepithelial carcinoma with focal AdCC-like histology.

Conclusions

PLAG1 expression is specific to pleomorphic adenoma. SOX10 expression is helpful to rule out excretory duct origin tumor, but its diagnostic value is relatively low. Myb is useful for diagnosing AdCC when histology is unclear in the surgical specimen.

Recurrent rearrangements of the PLAG1 and HMGA2 genes in lacrimal gland pleomorphic adenoma and carcinoma ex pleomorphic adenoma

PURPOSE

Lacrimal gland tumours constitute a wide spectrum of neoplastic lesions that are histologically similar to tumours of the salivary gland. In the salivary gland, pleomorphic adenoma (PA) is frequently characterized by recurrent chromosomal rearrangements of the PLAG1 and HMGA2 genes, a genetic feature retained in carcinoma ex pleomorphic adenoma (ca-ex-PA) that makes it possible to distinguish ca-ex-PA from de novo carcinomas. However, whether PLAG1 and HMGA2 gene rearrangements are found in lacrimal gland PA and ca-ex-PA is not known.

METHODS

Twenty-one lacrimal gland PAs and four ca-ex-PAs were retrospectively reviewed and subjected to break-apart fluorescence in situ hybridization (FISH) for rearrangements of the PLAG1 gene. Cases without PLAG1 abnormalities were subjected to HMGA2 break-apart FISH. Immunohistochemical staining for PLAG1 and HMGA2 protein was performed and correlated with gene status.

RESULTS

Sixteen of 21 PAs showed rearrangement of PLAG1 and were all positive for PLAG1 protein. Two of the remaining five PAs showed rearrangement of HMGA2 and were the only cases positive for HMGA2 with immunohistochemistry. The three FISH-negative PAs expressed PLAG1 protein. All four ca-ex-PAs showed rearrangement of PLAG1 and expressed PLAG1 protein. None of the de novo carcinomas showed rearrangement of either of the two genes or expression of the two proteins.

CONCLUSION

Rearrangement of PLAG1 and HMGA2 and expression of the corresponding proteins are frequent and specific findings in lacrimal gland PA and ca-ex-PA. The mechanism for PLAG1 overexpression in FISH-negative PAs is yet to be clarified.

MDM2 and CDK4 amplifications are rare events in salivary duct carcinomas

Salivary duct carcinoma (SDC) is an aggressive adenocarcinoma of the salivary glands associated with poor clinical outcome. SDCs are known to carry TP53 mutations in about 50%, however, only little is known about alternative pathogenic mechanisms within the p53 regulatory network. Particularly, data on alterations of the oncogenes MDM2 and CDK4 located in the chromosomal region 12q13-15 are limited in SDC, while genomic rearrangements of the adjacent HMGA2 gene locus are well documented in subsets of SDCs. We here analyzed the mutational status of the TP53 gene, genomic amplification of MDM2, CDK4 and HMGA2 rearrangement/amplification as well as protein expression of TP53 (p53), MDM2 and CDK4 in 51 de novo and ex pleomorphic adenoma SDCs.

25 of 51 cases were found to carry TP53 mutations, associated with extreme positive immunohistochemical p53 staining levels in 13 cases. Three out of 51 tumors had an MDM2 amplification, one of them coinciding with a CDK4 amplification and two with a HMGA2 rearrangement/amplification. Two of the MDM2 amplifications occurred in the setting of a TP53 mutation. Two out of 51 cases showed a CDK4 amplification, one synchronously being MDM2 amplified and the other one displaying concurrent low copy number increases of both, MDM2 and HMGA2.

In summary, we here show that subgroups of SDCs display genomic amplifications of MDM2 and/or CDK4, partly in association with TP53 mutations and rearrangement/amplification of HMGA2. Further research is necessary to clarify the role of chromosomal region 12q13-15 alterations in SDC tumorigenesis and their potential prognostic and therapeutic relevance.

Epithelial-Myoepithelial Carcinoma: Frequent Morphologic and Molecular Evidence of Preexisting Pleomorphic Adenoma, Common HRAS Mutations in PLAG1-intact and HMGA2-intact Cases, and Occasional TP53, FBXW7, and SMARCB1 Alterations in High-grade Cases

We hypothesized that there is a relationship between the preexisting pleomorphic adenoma [PA]), histologic grade of epithelial-myoepithelial carcinomas (EMCAs), and genetic alterations. EMCAs (n=39) were analyzed for morphologic and molecular evidence of preexisting PA (PLAG1, HMGA2 status by fluorescence in situ hybridization, FISH, and FGFR1-PLAG1 fusion by next-generation sequencing, NGS). Twenty-three EMCAs were further analyzed by NGS for mutations and copy number variation in 50 cancer-related genes. On the basis of combined morphologic and molecular evidence of PA, the following subsets of EMCA emerged: (a) EMCAs with morphologic evidence of preexisting PA, but intact PLAG1 and HMGA2 (12/39, 31%), (b) Carcinomas with PLAG1 alterations (9/39, 23%), or (c) HMGA2 alterations (10/39, 26%), and (d) de novo carcinomas, without morphologic or molecular evidence of PA (8/39, 21%). Twelve high-grade EMCAs (12/39, 31%) occurred across all subsets. The median disease-free survival was 80 months (95% confidence interval, 77-84 mo). Disease-free survival and other clinicopathologic parameters did not differ by the above defined subsets. HRAS mutations were more common in EMCAs with intact PLAG1 and HMGA2 (7/9 vs. 1/14, P<0.001). Other genetic abnormalities (TP53 [n=2], FBXW7 [n=1], SMARCB1 deletion [n=1]) were seen only in high-grade EMCAs with intact PLAG1 and HMGA2. We conclude that most EMCAs arose ex PA (31/39, 80%) and the genetic profile of EMCA varies with the absence or presence of preexisting PA and its cytogenetic signature. Progression to higher grade EMCA with intact PLAG1 and HMGA2 correlates with the presence of TP53, FBXW7 mutations, or SMARCB1 deletion.

Multi-dimensional genomic analysis of myoepithelial carcinoma identifies prevalent oncogenic gene fusions

Myoepithelial carcinoma (MECA) is an aggressive salivary gland cancer with largely unknown genetic features. Here we comprehensively analyze molecular alterations in 40 MECAs using integrated genomic analyses. We identify a low mutational load, and high prevalence (70%) of oncogenic gene fusions. Most fusions involve the PLAG1 oncogene, which is associated with PLAG1 overexpression. We find FGFR1-PLAG1 in seven (18%) cases, and the novel TGFBR3-PLAG1 fusion in six (15%) cases. TGFBR3-PLAG1 promotes a tumorigenic phenotype in vitro, and is absent in 723 other salivary gland tumors. Other novel PLAG1 fusions include ND4-PLAG1; a fusion between mitochondrial and nuclear DNA. We also identify higher number of copy number alterations as a risk factor for recurrence, independent of tumor stage at diagnosis. Our findings indicate that MECA is a fusion-driven disease, nominate TGFBR3-PLAG1 as a hallmark of MECA, and provide a framework for future diagnostic and therapeutic research in this lethal cancer.

Myoepithelial carcinoma (MECA) is a rare aggressive salivary gland cancer. Here, the authors analyze the genomic landscape of MECA and identify a high prevalence of oncogenic gene fusions, primarily PLAG1 fusions, highlighting TGFBR3-PLAG1 as a potential hallmark of MECA.

PLAG1 immunohistochemistry is a sensitive marker for pleomorphic adenoma: a comparative study with PLAG1 genetic abnormalities

AIMS

Pleomorphic adenoma gene 1 (PLAG1) gene rearrangement is the most common genetic abnormality in pleomorphic adenoma (PA), resulting in overexpression of PLAG1 protein. PA and carcinoma ex pleomorphic adenoma (CA ex-PA) can mimic various benign and malignant salivary gland tumours. The aims of this study are to evaluate the sensitivity and specificity of PLAG1 immunohistochemistry (IHC) in the differential diagnosis of PA and CA ex-PA and to compare the PLAG1 immunohistochemical results to PLAG1 gene abnormalities as detected by fluorescence in-situ hybridisation (FISH).

METHODS AND RESULTS

PLAG1 immunostaining was performed on 83 salivary gland tumours, including 23 PA, 15 CA ex-PA and 45 other salivary gland tumours. In addition, PLAG1 FISH was performed in 44 cases for the presence of gene rearrangements/amplifications. The results showed high sensitivity of PLAG1 IHC in 96% of PA; however, discordant results between PLAG1 FISH abnormalities and IHC were noted in 15 of 44 cases (34%). Seven PA, four de-novo myoepithelial carcinomas and one basal cell adenocarcinoma had negative FISH results, but were positive for IHC; while three salivary duct carcinomas (SDC) ex-PA were positive for FISH but negative for IHC. PLAG1 IHC can differentiate CA ex-PA from de-novo SDC (P = 0.02), but not from de-novo myoepithelial carcinoma. PLAG1 IHC is a sensitive marker for PA. This could be due to PLAG1 gene abnormalities beyond FISH resolution.

CONCLUSIONS

A negative PLAG1 IHC might be helpful in excluding a PA diagnosis. Interestingly, in the context of CA ex-PA, FISH is more sensitive than IHC in detecting PLAG1 abnormalities.

HMGA2 is a specific immunohistochemical marker for pleomorphic adenoma and carcinoma ex-pleomorphic adenoma

AIMS

Accurate classification of salivary gland neoplasms may be challenging, owing to morphological overlap, particularly in small biopsies. Recurrent translocations involving the high-mobility group AT-hook 2 (HMGA2) gene are present in a subset of pleomorphic adenomas (PAs) and carcinoma ex-pleomorphic adenomas (CA ex-PAs). The aim of this study was to evaluate immunohistochemical HMGA2 expression in 225 salivary gland tumours, including 56 PAs, 37 CA ex-PAs, and 132 potential histological mimics, to determine its diagnostic utility.

METHODS AND RESULTS

HMGA2 expression was identified in 19 PAs (33.9%) and nine CA ex-PAs (24.3%). Expression was strong and diffuse throughout all PAs, and in four of nine positive CA ex-PAs. In five CA ex-PAs, HMGA2 showed weak-to-strong multifocal staining within the carcinomatous component, and strong diffuse HMGA2 expression in the residual PA. Among histological mimics, six de-novo salivary duct carcinomas (28.5%), three epithelial-myoepithelial carcinomas (33.3%) and one case each of myoepithelioma and basal cell adenoma expressed HMGA2. Fluorescence in-situ hybridization for HMGA2 rearrangement performed on a subset of tumours that showed diffuse HMGA2 expression in PAs and CA ex-PAs was frequently associated with rearrangement of the HMGA2 locus, whereas cases of de-novo salivary duct carcinoma, or CA ex-PA with limited or no HMGA2 expression, had an intact HMGA2 locus.

CONCLUSIONS

HMGA2 expression is a highly specific (96.2%), but low-sensitivity (29.8%), marker for PA and CA ex-PA when compared with histological mimics, and is frequently associated with rearrangement of the HMGA2 locus.

Use of fluorescent in-situ hybridisation in salivary gland cytology: A powerful diagnostic tool

OBJECTIVE

Salivary gland cytology is challenging because it includes a diversity of lesions and a wide spectra of tumours. Recently, it has been reported that many types of salivary gland tumours have specific molecular diagnostic signatures that could be identified by fluorescent in-situ hybridisation (FISH). The aim of the present study was to demonstrate the feasibility and efficiency of FISH on routine cytological salivary gland smears.

METHODS

FISH was conducted on 37 cytological salivary gland smears from 34 patients. According to the cytological diagnosis suspected, MECT1/MAML2 gene fusion and rearrangements of PLAG1, MYB, or ETV6 were analysed. The presence and percentages of cells that had gene rearrangements were evaluated. Results were compared with the histological surgical samples, available from 26 patients.

RESULTS

The PLAG1 rearrangement was observed in 12/20 (60%) cases of pleomorphic adenoma. MECT1/MAML2 gene fusion was observed in 1:2 mucoepidermoid carcinomas but was not observed in five other tumours (two pleomorphic adenomas, one Warthin's tumour, one mammary analogue secretory carcinoma [MASC] and one cystic tumour). MYB rearrangement was observed in 4/4 adenoid cystic carcinomas. ETV6-gene splitting identified one MASC.

CONCLUSION

Overall, FISH had a specificity of 100% and a sensitivity of 66.7%. When FISH and cytological analyses were combined, the overall sensitivity was increased to 93.3%. It can thus be concluded that when the FISH analysis is positive, the extent of surgery could be determined with confidence pre-operatively without needing a diagnosis from a frozen section.

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.

Myoepithelial Carcinoma of the Paracecal Mesentery: Aggressive Behavior of a Rare Neoplasm at an Unusual Anatomic Site

Myoepithelial tumors of the soft tissues represent a rare group of neoplasms that vary in their clinical behavior, pathologic features and genetics. They are histopathologically typified by a myoepithelial immunohistochemical phenotype, of expression of one or more epithelial markers, S100 protein and smooth muscle actin. Because of their rarity and occurrence over a wide age range and at a variety of anatomic sites, they can be difficult to diagnose due to the lack of familiarity by physicians, which is compounded by their spectrum of histologic features and morphologic overlap with several other neoplasms. Recent genetic insights have aided classification, and it is increasingly understood that soft tissue myoepithelial neoplasms can be stratified into two distinct morphologic and genetic subgroups. We describe a case of a 44-year-old man who was diagnosed with a primary myoepithelial neoplasm of the paracecal mesentery, which showed aggressive local recurrence after four years. The tumor was composed of cords of ovoid cells within chondromyxoid stroma, and displayed a characteristic pancytokeratin, S100 protein and smooth muscle actin-positive myoepithelial immunoprofile. Primary myoepithelioma has not been previously described at this site, and this case highlights this varied family of tumors, emphasizes the need to consider myoepithelial tumor in the differential diagnoses of carcinoma variants occurring in the bowel or mesentery, and also adds to the number of reported myoepithelial neoplasms showing markedly aggressive behavior.

New Developments in Salivary Gland Pathology: Clinically Useful Ancillary Testing and New Potentially Targetable Molecular Alterations

Accurate diagnosis of salivary gland tumors can be challenging because of the many diagnostic entities, the sometimes extensive morphologic overlap, and the rarity of most tumor types. Ancillary testing is beginning to ameliorate some of these challenges through access to newer immunohistochemical stains and fluorescence in situ hybridization probes, which can limit differential diagnostic considerations in some cases. These ancillary testing strategies are especially useful in small biopsy samples, including aspiration cytology. Molecular techniques are also expanding our understanding of salivary gland tumor pathology and are helping to identify potential targets that may improve treatment for some of these tumors. Here, we summarize the clinical use of new immunohistochemical markers in our practice and review the current understanding of chromosomal rearrangements in salivary gland tumor pathology, emphasizing the prospects for exploiting molecular alterations in salivary gland tumors for diagnosis and targeted therapy. We find that immunohistochemistry and fluorescence in situ hybridization are powerful tools toward the diagnosis of salivary gland tumors, especially when used in a systematic manner based on morphologic differential-diagnostic considerations. As new targeted therapies emerge, it will become increasingly vital to incorporate appropriate molecular testing into the pathologic evaluation of salivary gland cancers.

Diagnosis and Management of Malignant Salivary Gland Tumors of the Parotid Gland

Malignant parotid tumors are heterogeneous and diverse. Accurate diagnosis requires a pathologist familiar with the various histologic subtypes, immunohistochemistry stains, and common translocations. Clinical course varies according to tumor subtype, ranging from indolent, slow-growing adenoid cystic carcinoma to rapidly progressive, possibly fatal, salivary ductal carcinoma. Histologic grade is important in prognosis and therapy. Surgery remains the mainstay of treatment when negative margins can be achieved. Radiation improves locoregional control of tumors with high-risk features. Chemotherapy for parotid tumors can be disappointing. Studies of new targeted therapies have not offered significant benefits.

Beta-catenin in disease

In continuation with the previous review on “β-catenin in health”, in this review we discuss the role of β-catenin in the pathogenesis of common oral lesions in the oral and maxillofacial region- oral potentially malignant disorders, their progression to oral squamous cell carcinoma, salivary gland tumors and odontogenic tumours. This review is based on a pubmed search of all the lesions included in the review.

Molecular Pathology: Predictive, Prognostic, and Diagnostic Markers in Salivary Gland Tumors

Although initial attempts at using ancillary studies in salivary gland tumor classification were viewed with skepticism, numerous advances over the past decade have established a role for assessment of molecular alterations in the diagnosis and potential prognosis and treatment of salivary gland tumors. Many monomorphic salivary tumors are now known to harbor defining molecular alterations, usually translocations. Pleomorphic, high-grade carcinomas tend to have complex alterations that are often further limited by inaccuracy of initial classification by morphologic and immunophenotypic features. Next-generation sequencing techniques have great potential in many aspects of salivary gland tumor classification and biomarker discovery.

PLAG1: An Immunohistochemical Marker with Limited Utility in Separating Pleomorphic Adenoma from Other Basaloid Salivary Gland Tumors

OBJECTIVE

Fine-needle aspiration (FNA) diagnosis of salivary gland neoplasms is often challenging. Differentiating between pleomorphic adenomas (PA) and other basaloid neoplasms, especially basal cell adenoma (BCA) and adenoid cystic carcinoma (AdCC), can be difficult in cellular aspirates. PLAG1 (PA gene 1) is a proto-oncogene, which is frequently rearranged in PAs, leading to the aberrant expression of its protein. PLAG1 IHC expression has been reported to be positive in most PAs. The aim of this study was to evaluate the sensitivity and specificity of PLAG1 to differentiate PA from other basaloid neoplasms.

STUDY DESIGN

Immunohistochemical evaluation of PLAG1 was performed on 125 cases (52 FNAs and 73 surgical excisions). Nuclear staining of tumor cells was scored by the intensity and percentage of positive tumor cells. A combined score of >5 was defined as positive.

RESULTS AND CONCLUSION

The sensitivity (55%) and specificity (75%) of PLAG1 in diagnosing PA in FNAs is relatively modest thus limiting its diagnostic utility. BCAs and AdCCs showed PLAG1 false positivity, in surgical excision specimens and less so in FNAs. This may be due to limited sampling or tumor heterogeneity. Hence, PLAG1 is a modest marker for PAs in FNAs.

Loss of expression of Plag1 in malignant transformation from pleomorphic adenoma to carcinoma ex pleomorphic adenoma

PLAG1 (pleomorphic adenoma gene 1) is frequently activated in pleomorphic adenoma (PA). Carcinoma ex pleomorphic adenoma (CXPA) arises in PA, and PLAG1 expression is believed to be maintained from PA to CXPA, as it can contribute to the carcinogenesis process. To evaluate if PLAG1 is a good marker of malignant transformation from PA to CXPA as well as to evaluate if PLAG1 expression is associated with progression and histopathologic subtype of CXPA. Forty PAs, 21 residual PAs (without malignant transformation), and 40 CXPAs were analyzed by immunohistochemistry with PLAG1 antibody. The proportion of positive neoplastic cells was assessed according to a 2-tiered scale: >10% to 50%, and >50% positive cells. The CXPA group was classified according to histopathologic subtype and invasiveness degree. Thirty-seven PAs (92.5%), 15 residual PAs (71%), and 14 CXPAs (35%) were positive for PLAG1. In relation to the CXPA group, among the intracapsular cases, myoepithelial carcinoma and epithelial-myoepithelial carcinoma showed the highest level of PLAG1 expression. PLAG1 expression is lost when PA undergoes malignant transformation, possibly due to other pathway activation and different clone cells. In addition, PLAG1 expression seems to be present mainly in low-grade carcinomas and in cases with early phase of invasion, due to its regulation of oncogene-induced cell senescence. In CXPA, PLAG1 expression was most associated with myoepithelial differentiation. This way, loss of PLAG1 expression can be considered a hallmark of CXPA carcinogenesis, mainly when there is only epithelial differentiation.