Fluorescence in situ hybridization for detection of MAML2 rearrangements in oncocytic mucoepidermoid carcinomas: utility as a diagnostic test

Salivary Gland Cancers in the Era of Molecular Analysis: The Role of Tissue and Liquid Biomarkers

Background: Salivary gland cancers (SGCs) are a rare and heterogeneous group of malignancies, accounting for approximately 5% of head and neck cancers. Despite their rarity, advances in molecular profiling have revealed a variety of genetic and molecular pathways, many of which are potentially actionable with targeted therapies. Methods: We reviewed the current literature involving the molecular landscape of SGCs, encompassing the diagnostic and prognostic value of tissue and liquid biomarkers and the potential therapeutic targets across various histological subtypes. Results: Our review highlights key molecular diagnostic findings such as the CRTC1-MAML2 fusion in mucoepidermoid carcinoma and MYB-NFIB rearrangements in adenoid cystic carcinoma, but also targetable alterations such as HER2 and AR positivity in salivary duct carcinoma and ETV6-NTRK3 fusion in secretory carcinoma. Liquid biopsy (both blood- or salivary-based), including circulating tumor DNA, circulating tumor cells, and miRNAs, offers novel, noninvasive approaches for disease monitoring and personalized treatment. Emerging therapies such as HER2 inhibitors, androgen deprivation therapy, and TRK inhibitors underscore the shift towards precision oncology in managing these malignancies. Conclusions: Despite promising advances, challenges remain due to the rarity and phenotypic heterogeneity of SGCs, emphasizing the need for molecularly stratified clinical trials. This review presents an overview of tissue and liquid biomarkers, focusing on molecular targets and therapeutic innovations that lay the foundation for improved diagnostic and treatment strategies for SGCs.

Reappraisal of Oncocytic Adenocarcinoma: Unveiling Its Connection to Oncocytic Variants of Salivary Duct Carcinoma and Mucoepidermoid Carcinoma Through ImmunoHisto-Molecular Perspectives

Oncocytic adenocarcinoma (OC) of the salivary glands is a rare and controversial entity. It was recently reclassified as "salivary carcinoma NOS and emerging entities" in the 2022 WHO classification of head and neck tumors. The lack of specific molecular alterations and its potential affiliation with other salivary gland carcinomas, such as the oncocytic mucoepidermoid carcinomas (OMEC) or the oncocytic subtype of salivary duct carcinomas (OSDC) justified this reclassification. It is becoming essential to clarify the complex spectrum of potential diagnoses surrounding oncocytic tumors. The objective of this study was to explore the histologic features, as well as the immunohistochemical and molecular profiles, of cases previously diagnosed as OC or OMEC of the salivary glands. This study involved 28 cases of carcinomas with a predominantly oncocytic component. The sex distribution was equal. The median age was 59 years (range 10 to 89). Most of these cases originated from the parotid gland (25/28). The mean tumor size was 2.4 cm (range 0.5 to 6.5). Primary immuno-morphological and mutation/gene fusion profiles reclassified mainly (64.3%, 18/28). Most of them were reclassified in descending order as OSDC (8/18), OMEC (5/18), and OC (2/18). But 3 cases remained unclassified (3/18). The transcriptomic analysis found a proximity of their transcriptomic profile with the OMEC group and a distance from the OSDCs. These findings imply that OC is not distinct but represents oncocytic variants of other salivary carcinomas. It underscores the importance of thorough morphologic, immunohistochemical, and molecular examinations to accurately diagnose carcinomas with predominant oncocytic components in the salivary glands.

Salivary Gland Oncocytomas. A Systematic Review

BACKGROUND

Oncocytoma is a primary benign epithelial neoplasm comprising less than 2% of salivary tumors with a low recurrence rate.

METHODS

A systematic review of documented case reports and case series of oncocytomas is presented. Searches from different databases were performed to identify articles from 1956 to 2024. The variables included were gender, age, symptoms, duration time before diagnosis, type of gland, histological features, special or immunohistochemical evaluation, treatment, follow-up, recurrence, and relation with a medical condition or syndrome.

RESULTS

Of the 147 cases reported, 53.1% affected females, and 46.9% were in males. The average age was 58.7 years, and the mean size was 2.3 cm. The most common clinical presentation was swelling (92.6%) and 66.7% were asymptomatic. The parotid was the most commonly affected gland with 66% of cases, the submandibular gland with 23.3%, and the minor salivary glands with Phosphotungstic acid-hematoxylin (PTAH) was the most common special stain used in 36.7%, followed by a combination with Periodic acid-Schiff (PAS) with and without diastase in 26.6%. Excisional biopsy was the most common treatment in 38.1% followed by superficial parotidectomy in 32.7%. Follow-up was 34.7 months on average. Bilateral oncocytomas were found in 4.8% with a 6 to 1 female-male proportion. Recurrence was found in 2.7% and association with Birt-Hogg-Dube (BHD) syndrome was 8.2%.

CONCLUSION

Salivary oncocytoma is a rare epithelial neoplasm with nonspecific clinical presentations. Diagnosis can be suspected on cytology and confirmed by histologic examination. The lesion has an indolent clinical course and most of the reported cases did not recur. There seems to be an association between bilateral oncocytomas and females and a low but interesting association with BHD. Overall, this review serves to better highlight the features of this rare benign neoplasm.

New Entities and Concepts in Salivary Gland Tumor Pathology: The Role of Molecular Alterations

CONTEXT.—

Salivary gland tumors are rare tumor types for which the molecular understanding has resulted in a rapid expansion and shuffling of entities. These changes are reflected in the 5th edition World Health Organization Classification of Head and Neck Tumours (WHO 5th edition), although many nuances still remain.

OBJECTIVE.—

To review how molecular alterations have helped recategorize, justify, and reinstate entities into our lexicon as well as defining interrelationships between categories, new entities, and subtypes. Furthermore, newer theranostic applications to molecular phenotype will be summarized.

DATA SOURCES.—

World Health Organization Classification of Head and Neck Tumours (WHO 3rd through 5th editions), literature review, and personal and institutional experience.

CONCLUSIONS.—

Molecular alterations have helped reclassify, retain, and create new categories by augmenting rather than replacing standard criteria. Key entities that have emerged include sclerosing polycystic adenoma, microsecretory adenocarcinoma, and mucinous adenocarcinoma. Molecular phenotypes solidify the range of morphology in established entities such as mucoepidermoid carcinoma and facilitate connectivity between entities. Molecular characteristics now allow for targeted therapeutic approaches for secretory carcinoma and adenoid cystic carcinoma.

Fusions in salivary gland neoplasms: a review of practical diagnostic applications

There is an ongoing explosion of new information regarding the underlying molecular alterations driving a variety of salivary gland neoplasms. The volume of this emerging data makes it difficult to keep up with and may cause pathologists to believe that salivary gland neoplasms cannot be diagnosed without genetic analysis. This review focuses on the practical diagnostic applications of molecular tools in surgical pathology specimens.

Expanding the cytological and architectural spectrum of mucoepidermoid carcinoma: The key to solving diagnostic problems in morphological variants

Mucoepidermoid carcinoma (MEC) is the most common malignant salivary gland tumor. Varying sized cysts and sheets composed of three cell types (epidermoid, intermediate, and mucous cells) with varying degrees of atypia form the characteristic histological appearance of MEC. MEC frequently contains a wide variety of modified tumor cells and can be entirely cystic or completely solid. Under these circumstances, MEC requires critical differentiation from many mimickers, ranging from simple cysts and benign tumors to high-grade carcinomas. Tumor-associated lymphoid proliferation and sclerotic changes in the stroma also contribute to diagnostic difficulties. Several well-known diagnostically challenging variants (oncocytic, clear cell, spindle cell, and sclerosing) exist in MEC. With the advent of studies on specific CRTC1/3::MAML2 fusion genes in MEC, newly proposed subtypes have emerged, including Warthin-like and non-sebaceous lymphadenoma-like MECs. In addition to the recently defined mucoacinar variant with a serous cell phenotype, MEC devoid of squamous differentiation has also been reported, implying the need to reconsider this basic concept. In this article, we outline the general clinical features and MAML2 status of conventional MEC and review the cytoarchitectural subtypes, with an emphasis on a pitfall in the interpretation of this histologically diverse single entity.

Case report: The diagnostic pitfall of Warthin-like mucoepidermoid carcinoma

Warthin-like mucoepidermoid carcinoma (WL-MEC) is a newly reported variant of mucoepidermoid carcinoma. Its histological feature is easy to confused with metaplastic Warthin Tumor, and its relationship with Warthin tumor in histogenesis is controversial. In this study, we presented two cases of WL-MEC, discussing their clinicopathological and molecular features. Notably, one case was initially misdiagnosed during the first onset of the tumor. Case 1 was a 60-year-old female with a mass in the right parotid gland. Case 2 featured a 29-year-old male who developed a lump at the original surgical site 6 months after a "Warthin tumor" resection from the submandibular gland. Histologically, both tumor exhibited a prominent lymphoid stroma and cystic pattern, accompanied by various amounts of epithelial nests composed of squamoid cells, intermediate cells and mucinous cells. The characteristic eosinophilic bilayer epithelium of Warthin tumor was not typically presented in either case. Both cases tested positive for MAML2 gene rearrangement. To contextualize our findings, we conducted a comprehensive review of forty-eight WL-MEC cases documented in the English literature, aiming to synthesizing a reliable differential diagnostic approach. WL-MEC is a rare yet clinically relevant variant, posing a diagnostic pitfall for pathologists. Our study underscores the importance of a meticulous evaluation of both clinical and histological features, coupled with the detection of MAML2 rearrangement, as a credible method for distinguishing WL-MEC from other benign and malignant lesions, particularly metaplastic Warthin tumor.

Keratocystoma: A Distinctive Salivary Gland Neoplasm Characterized by RUNX2 Rearrangements

Keratocystoma is a rare salivary gland lesion that has been reported primarily in children and young adults. Because of a scarcity of reported cases, very little is known about it, including its molecular underpinnings, biological potential, and histologic spectrum. Purported to be a benign neoplasm, keratocystoma bears a striking histologic resemblance to benign lesions like metaplastic Warthin tumor on one end of the spectrum and squamous cell carcinoma on the other end. This overlap can cause diagnostic confusion, and it raises questions about the boundaries and definition of keratocystoma as an entity. This study seeks to utilize molecular tools to evaluate the pathogenesis of keratocystoma as well as its relationship with its histologic mimics. On the basis of targeted RNA sequencing (RNA-seq) results on a sentinel case, RUNX2 break-apart fluorescence in situ hybridization (FISH) was successfully performed on 4 cases diagnosed as keratocystoma, as well as 13 cases originally diagnosed as tumors that morphologically resemble keratocystoma: 6 primary squamous cell carcinomas, 3 metaplastic/dysplastic Warthin tumors, 2 atypical squamous cysts, 1 proliferating trichilemmal tumor, and 1 cystadenoma. RNA-seq and/or reverse transcriptase-PCR were attempted on all FISH-positive cases. Seven cases were positive for RUNX2 rearrangement, including 3 of 4 tumors originally called keratocystoma, 2 of 2 called atypical squamous cyst, 1 of 1 called proliferating trichilemmal tumor, and 1 of 6 called squamous cell carcinoma. RNA-seq and/or reverse transcriptase-PCR identified IRF2BP2::RUNX2 in 6 of 7 cases; for the remaining case, the partner remains unknown. The cases positive for RUNX2 rearrangement arose in the parotid glands of 4 females and 3 males, ranging from 8 to 63 years old (mean, 25.4 years; median, 15 years). The RUNX2 -rearranged cases had a consistent histologic appearance: variably sized cysts lined by keratinizing squamous epithelium, plus scattered irregular squamous nests, with essentially no cellular atypia or mitotic activity. The background was fibrotic, often with patchy chronic inflammation and/or giant cell reaction. One case originally called squamous cell carcinoma was virtually identical to the other cases, except for a single focus of small nerve invasion. The FISH-negative case that was originally called keratocystoma had focal cuboidal and mucinous epithelium, which was not found in any FISH-positive cases. The tumors with RUNX2 rearrangement were all treated with surgery only, and for the 5 patients with follow-up, there were no recurrences or metastases (1 to 120 months), even for the case with perineural invasion. Our findings solidify that keratocystoma is a cystic neoplastic entity, one which appears to consistently harbor RUNX2 rearrangements, particularly IRF2BP2::RUNX2 . Having a diagnostic genetic marker now allows for a complete understanding of this rare tumor. They arise in the parotid gland and affect a wide age range. Keratocystoma has a consistent morphologic appearance, which includes large squamous-lined cysts that mimic benign processes like metaplastic Warthin tumor and also small, irregular nests that mimic squamous cell carcinoma. Indeed, RUNX2 analysis has considerable promise for resolving these differential diagnoses. Given that one RUNX2 -rearranged tumor had focal perineural invasion, it is unclear whether that finding is within the spectrum of keratocystoma or whether it could represent malignant transformation. Most important, all RUNX2 -rearranged cases behaved in a benign manner.

Critical Appraisal of Histologic Grading for Mucoepidermoid Carcinoma of Salivary Gland: Is an Objective Prognostic 2-tiered Grading System Possible?

Multiple 3-tiered grading systems exist for mucoepidermoid carcinoma (MEC), leading to controversial results on the frequency and prognostic values of each grade. We aimed to identify prognostic histologic factors and to evaluate grading schemes in this retrospective study of 262 resected primary head and neck MECs. The rate of nodal metastasis was 8.4%. Large tumor size, tumor fibrosis, infiltrative border, lymphovascular invasion, perineural invasion, atypical mitosis, mitotic index (MI) ≥4/2 mm 2 (4/10 HPFs), necrosis, and pT4 stage were associated with increased risk of nodal metastasis. The 5-year recurrence-free survival (RFS) was 95%. Significant prognostic factors for RFS included infiltrative border, tumor-associated lymphoid stroma, architectural patterns (macrocystic, microcystic, and noncystic), anaplasia, atypical mitosis, MI, necrosis, lymphovascular invasion, margin, pT stage, and tumor size. Nuclear anaplasia, high mitotic rate, and ≥25% microcystic component were significant independent prognostic factors on multivariate survival analysis. There was no significant difference between low-grade (LG) and intermediate-grade (IG) MECs in terms of risk of nodal metastasis and outcomes using all 4 known grading systems. Rather, high-grade MEC was consistently associated with an increased risk of nodal metastasis at presentation and decreased RFS and distant metastasis-free survival (DMFS) compared with the LG/IG MECs. We therefore recommend simplifying MEC grading to a 2-tiered grading scheme using MI and/or tumor necrosis. Using a 2-tiered grading, high-grade histology independently predict RFS, and is associated with a 25% risk of nodal metastasis, a 5-year RFS of 76%, and a 5-year DMFS of 76%, whereas LG MEC has a nodal metastasis rate of 7.0%, 5-year RFS of 97% and 5-year DMFS of 99%.

Glandular Odontogenic Cyst: a Case Report and Literature Review

Background

The glandular odontogenic cyst is now a well-known entity comprising < 0.5% of all odontogenic cysts with a recent review tabulating about 200 cases in the English literature. Glandular odontogenic cyst shows epithelial features that simulate salivary gland or glandular differentiation. The importance of glandular odontogenic cyst relates to the fact that it has a high recurrence rate and shares overlapping histologic features with central mucoepidermoid carcinoma. The purpose of this paper is to describe the clinical, radiological, and histopathological features of a case of glandular odontogenic cyst with the course of treatment and 9-years follow-up, followed by a review of the literature.

Methods

A 63-year-old male was referred for further investigation of a mandibular radiolucency observed by his general dental practitioner. The main complaint was a murmuring sensation in the lower jaw right side. Radiological examination revealed a well-defined, unilocular, radiolucent lesion, involving the right mandible with 17 and 68 mm in mediolaterally and anteroposterior dimension, respectively.

Results

A total enucleation of the cystic lesion and surgical extraction of tooth #46, #47 and #48, was performed under local anaesthesia. Histopathologic examination revealed a glandular odontogenic cyst.

Conclusions

Glandular odontogenic cyst shows no pathognomonic clinico-radiographic characteristics, and therefore in many cases it resembles a wide spectrum of lesions. Diagnosis can be extremely difficult due to histopathological similarities with dentigerous cyst, lateral periodontal cyst and central mucoepidermoid carcinoma. Therefore a careful histopathological examination and a long-term follow-up (preferably seven years) are required to rule out recurrences.

Molecular Targets in Salivary Gland Cancers: A Comprehensive Genomic Analysis of 118 Mucoepidermoid Carcinoma Tumors

INTRODUCTION

Salivary gland carcinomas (SGC) are histologically diverse cancers and next-generation sequencing (NGS) to identify key molecular targets is an important aspect in the management of advanced cases.

METHODS

DNA was extracted from paraffin embedded tissues of advanced SGC and comprehensive genomic profiling (CGP) was carried out to evaluate for base substitutions, short insertions, deletions, copy number changes, gene fusions and rearrangements. Tumor mutation burden (TMB) was calculated on approximately 1.25 Mb. Some 324 genes in the FoundationOne CDX panel were analyzed.

RESULTS

Mucoepidermoid carcinoma (MECa) mutations were assessed. CDKN2A and CDKN2B GA were common in mucoepidermoid carcinoma (MECa) (52.5 and 30.5%). PIK3CA was also common in MECa (16.9%). ERBB2 amplification/short variants (amp/SV) were found in MECa (5.9/0%). HRAS GA was common in MECa (14.4%) as well. Other targets, including BAP1, PTEN, and KRAS, were noted but had a low incidence. In terms of immunotherapy (IO)-predictive markers, TMB > 10 was more common in MECa (16.9%). PDL1 high was also seen in MECa (4.20%).

CONCLUSION

SGC are rare tumors with no FDA-approved treatment options. This large dataset reveals many opportunities for IO and targeted therapy contributing to the continuously increased precision in the selection of treatment for these patients.

Mucoepidermoid carcinoma may be devoid of squamoid cells by immunohistochemistry: expanding the histologic and immunohistochemical spectrum of MAML2- rearranged salivary gland tumours

Mucoepidermoid carcinoma (MEC) is historically defined by a mix of squamoid, intermediate, and mucous cells, but we have recently encountered several cases lacking immunoreactivity for squamous markers p40, p63, and CK5/6 despite MAML2 fusions. This study will characterise these unique tumours. Ten MEC were collected arising from the parotid gland (n = 4), submandibular gland (n = 2), nasopharynx (n = 1), base of tongue (n = 1), bronchus (n = 1), and trachea (n = 1). Six tumours were low-grade, two intermediate-grade, one high-grade, and one demonstrated low-grade areas with high-grade transformation. Four cases were oncocytic, four had clear-cell features, two had spindle cell features, and one high-grade MEC had prominent solid, cord-like, and micropapillary features. The tumours were negative for p40 (10/10), p63 (10/10), and CK5/6 (9/9). Targeted RNA sequencing demonstrated CRTC1::MAML2 in five cases, CRTC3::MAML2 in two, and a novel MAML2::CEP126 in the unusual high-grade case. In two cases with insufficient RNA, MAML2 fluorescence in situ hybridisation (FISH) showed rearrangement. Genetically-confirmed MEC may lack overt squamous differentiation by histology and immunohistochemistry. While most cases harboured canonical fusions and fit within the spectra of MEC variants with oncocytic, clear cell, and/or spindle cell features, one had a novel MAML2::CEP126 fusion and unusual morphology. In MEC without squamoid cells, the use of immunohistochemistry may hinder, rather than aid, the correct diagnosis. In such cases, MAML2 analysis is most useful. The historical definition of MEC as a carcinoma with squamoid, intermediate and mucous cells should be revisited.

MAML2 negative oncocytic mucoepidermoid carcinoma of submandibular gland

Background

Oncocytic mucoepidermoid carcinoma is a rare variant of mucoepidermoid carcinoma. Only a few cases are reported involving mostly the parotid gland with only four cases reported in the submandibular gland. Mastermind-like 2 (MAML2) translocation is detected in about 66% mucoepidermoid carcinoma and many oncocytic mucoepidermoid carcinoma.

Case presentation

We present a rare case of MAML2 negative oncocytic mucoepidermoid carcinoma of the submandibular gland in a 73-year-old female. CT revealed a large left submandibular gland mass. Submandibular gland resection with marginal mandibulectomy and ipsilateral neck dissection was performed. Grossly, a solid-cystic submandibular gland tumor was identified. Microscopic examination revealed an infiltrative proliferation of oncocytes. Foci of squamoid and intermediate cells with rare mucocytes were present. Two ipsilateral cervical lymph nodes and mandible were involved. Immunohistochemistry and special stains demonstrated positivity for p63, p40, CK5/6, mucicarmine and alcian blue. No MAML2 gene rearrangement was identified.

Conclusion

An awareness that MAML2 negative mucoepidermoid carcinoma exists will prevent misdiagnosis and incorrect treatment as many of its differential diagnoses are benign.

Primary Mucoepidermoid Carcinoma of the Lacrimal Apparatus

PURPOSE

In this study, we evaluated the clinicopathologic and molecular characteristics of lacrimal apparatus mucoepidermoid carcinoma (MEC) to define its typical diagnostic features.

DESIGN

Retrospective observational case series.

METHODS

Institutional pathology records between 2011 and 2021 were searched for all cases of lacrimal apparatus MEC.

RESULTS

A total of 2 male and 6 female patients ranging in age from 18 to 83 years (median 56, mean 54) were included. Six lacrimal apparatus MECs were found in the lacrimal gland, and 2 cases occurred in the lacrimal sac and nasolacrimal duct. Histologically, there were 6 cases of conventional MEC, 1 clear-cell variant of MEC, and 1 oncocytic variant of MEC for a total of 8 cases. There were 3 low-grade cases and 5 high-grade cases. All 8 cases were evaluated via immunohistochemistry, and the results were positive (scores 1-4) for pankeratin, 34betaE12, p63, p40, CK7, CK8, and CK19, with a relatively higher expression of p63 observed in high-grade MEC. The presence of human papillomavirus (HPV) type 6 DNA was found in 4 patients. MAML2 fluorescence in situ hybridization was positive for MAML2 rearrangement in 3 lacrimal gland tumors (2 low-grade and 1 high-grade). Six tumors were managed with radical resection, and 2 patients underwent orbital exenteration. Postoperative radiation therapy was delivered to 6 patients, and chemotherapy was administered to 1 patient.

CONCLUSIONS

MECs of the lacrimal apparatus are rare tumors, and the rate of MAML2 translocations is lower than that in salivary MECs. Lacrimal gland and lacrimal sac MECs may not be of the same subtypes intrinsically because of the difference in MAML2 translocation, anatomy, and clinical course. The etiologic function of HPV type 6 infection should be explored in lacrimal apparatus MECs. Radical surgery is the treatment of choice. The description of these unique findings may assist in the definitive diagnosis of and improve our understanding of lacrimal apparatus MEC.

The Milan System classification of Warthin tumor: A large institutional study of 124 cases highlighting cytologic features that limit definitive interpretation

BACKGROUND

Fine-needle aspiration (FNA) is highly accurate for the diagnosis of Warthin tumor (WT). However, there is a minor subset of WT cases that are more challenging to interpret. The goal of this study is to identify factors that limit definitive diagnosis of WT on FNA.

METHODS

All WT surgical specimens diagnosed during a 6.5-year study period were retrospectively identified and the preceding cytologic specimen diagnostic categories were analyzed. Of particular interest were WT cases with indeterminate or malignant interpretations. Cases that noted squamous or mucinous change in either the surgical or cytologic reports were also reviewed.

RESULTS

A total of 157 WT surgical specimens were identified, with 124 (79.0%) having prior FNAs. The distribution of cytologic diagnostic categories was 12 (9.7%) nondiagnostic, 10 (8.1%) nonneoplastic, 13 (10.5%) atypia of undetermined significance (AUS), 82 (66.1%) neoplasm: benign, 4 (3.2%) salivary gland neoplasm of uncertain malignant potential (SUMP), 2 (1.6%) suspicious for malignancy, and 1 (0.8%) malignant. Of the 20 cases in indeterminate/malignant categories, a majority noted either squamoid (9 of 20) or mucinous (2 of 20) changes. The remainder noted scant cellularity as a limiting factor to interpretation. Additionally, 27 cases mentioned squamous or mucinous change in the surgical or cytology report, with a wide spectrum of cytologic categorization including 2 (7.4%) nondiagnostic, 2 (7.4%) nonneoplastic, 7 (25.9%) AUS, 8 (29.6%) neoplasm: benign, 4 (14.8%) SUMP, 2 (7.4%) suspicious for malignancy, and 1 (3.7%) malignant.

CONCLUSIONS

This study identified 2 key causes for indeterminate or misclassification of WT on FNA: specimen hypocellularity and metaplastic changes. Recognition of the potential for squamous and mucinous metaplastic changes combined with observance of some helpful diagnostic clues such as the presence of crystalloids may aid in preventing diagnostic pitfalls.

Proceedings of the North American Society of Head and Neck Pathology, Los Angeles, CA, March 20, 2022: Emerging Entities in Salivary Gland Tumor Pathology

Salivary gland tumor pathology is one of the most challenging areas in all head and neck surgical pathology. Compounding its inherent difficulty are numerous novel entities, variants and concepts, most of which have been based on recent molecular discoveries. This review will serve to update the practicing pathologist on a selected group of emerging entities in salivary gland tumor pathology.

Mucoacinar Carcinoma: A Rare Variant of Mucoepidermoid Carcinoma

Mucoepidermoid carcinoma (MEC) is generally characterized by an admixture of mucous, epidermoid and intermediate type cells. Numerous variants morphologies are described and defined by stromal and/or cytoplasmic tinctorial characteristics. We now report 11 cases of MEC with serous acinar differentiation, reflecting a distal intercalated duct/acinar phenotype, which we designate as mucoacinar carcinomas. Seven patients were female while 4 were male with a mean age of 55 years (range: 21 to 72 y). Ten cases were from the parotid while 1 was from the submandibular gland. Mean size of the tumors was 1.8 cm (range: 0.7 to 4.5 cm). Three cases were low grade, 7 were intermediate grade, and 1 was high grade. Low to intermediate grade cases demonstrated prominent clear to vacuolated cells with focal serous acinar differentiation. The high-grade case showed a distinctive scattering of acinar cells interspersed between epidermoid cells. Periodic acid Schiff after diastase (9/9), SOX-10 (9/9), and DOG-1 (9/10) highlighted the acinar component. Six of 7 cases showed a focal acinar predominant NR4A3 expression. MAML2 fluorescence in situ hybridization was positive in all cases, in both acinar and mucoepidermoid components. Two cases tested by next generation sequencing showed standard CRTC1-MAML2 fusions. MSANTD3 and NR4A3 fluorescence in situ hybridization on the other hand were negative. Evidence thus suggests that mucoacinar carcinoma represents an acinar variant morphology in MEC, rather than a true MEC-acinic cell carcinoma hybrid, or collision tumor. The acinar differentiation, SOX-10, DOG-1, and even focal NR4A3 reactivity may thus be diagnostic pitfalls.

Immunocytochemistry for diagnostic cytopathology-A practical guide

Cytological specimens, which are obtained by minimally invasive methods, are an excellent source of diagnostic material. Sometimes they are the only material available for diagnosis as well as for prognostic/predictive markers. When cytomorphology is not straightforward, ancillary tests may be required for a definitive diagnosis to guide clinical management. Immunocytochemistry (ICC) is the most common and practical ancillary tool used to reach a diagnosis when cytomorphology is equivocal, to differentiate entities with overlapping morphological features, and to determine the cell lineage and the site of origin of a metastatic neoplasm. Numerous immunomarkers are available, and some are expressed in multiple neoplasms. To rule out entities within a differential diagnosis, the use of more than one marker, sometimes panels, is necessary. ICC panels for diagnostic purposes should be customised based on the clinical context and cytomorphology, and the markers should be used judiciously to preserve material for additional tests for targeted therapies in the appropriate setting. This review offers a practical guide for the use of ICC for diagnostic cytopathology, covering the most commonly encountered non-hematolymphoid diagnostic scenarios in various body sites.

Oncocytic Polyp in a Unicystic Mucoepidermoid Carcinoma of the Palate: A Unique Presentation

We report a palatal mucoepidermoid carcinoma (MEC) with unusual pathological features showing salivary duct cyst-like architecture, varied epithelial linings (excretory duct, mucous goblet cell, and apocrine epithelium phenotypes), scarce luminal tumor plaques, and a large intraluminal oncocytic polyp. To our knowledge, such a unicystic variant of MEC with pedicled oncocytic proliferation in the lumen is unprecedented in the literature. In this particular case, the microscopic diagnosis of MEC is problematic because of the large number of potential mimics.

Oncocytic intraductal carcinoma of salivary glands: a distinct variant with TRIM33-RET fusions and BRAF V600E mutations

AIMS

Salivary gland intraductal carcinoma (IDC) is a complex ductal neoplasm surrounded by a layer of myoepithelial cells. Recent insights have shown that there are three different types: intercalated duct-like, with frequent NCOA4-RET fusions; apocrine, with salivary duct carcinoma-like mutations; and mixed intercalated duct-like/apocrine, with RET fusions, including TRIM27-RET. In addition, an oncocytic IDC has been described, but it remains unclear whether it represents a fourth variant or simply oncocytic metaplasia of another IDC type. Our aim was to more completely characterize oncocytic IDC.

METHODS AND RESULTS

Six IDCs with oncocytic changes were retrieved from the authors' archives, from three men and three women ranging in age from 45 to 75 years (mean, 63 years). Five arose in the parotid gland, with one in an accessory parotid gland. Four patients with follow-up were free of disease after 1-23 months. Several immunostains (S100, mammaglobin, androgen receptor, and p63/p40) and molecular tools (RNA sequencing, RET fluorescence in-situ hybridisation, BRAF V600E VE1 immunohistochemistry, and Sanger sequencing) were applied. Histologically, the tumours were variably cystic with solid intracystic nodules often difficult to recognise as intraductal. In all, tumour ducts were positive for S100 and mammaglobin, negative for androgen receptor, and completely surrounded by myoepithelial cells positive for p63/p40. Molecular analysis revealed TRIM33-RET in two of six cases, NCOA4-RET in one of six cases, and BRAF V600E in two of six cases. One case had no identifiable alterations.

CONCLUSIONS

Oncocytic IDC shares similarities with intercalated duct-like IDC. Although additional verification is needed, the oncocytic variant appears to be sufficiently unique to be now regarded as the fourth distinct subtype of IDC. Because of its indolent nature, oncocytic IDC should be distinguished from histological mimics.

Recent updates in salivary gland tumors of the lung

Salivary gland tumors are uncommon primary lesions in the lung. Their morphologic, immunophenotypic, and molecular characteristics resemble those of their counterparts in the head and neck or elsewhere. Most common primary pulmonary salivary gland tumors include mucoepidermoid carcinoma, adenoid cystic carcinoma, and epithelial-myoepithelial carcinoma. The study of these neoplasms is hampered by their paucity. Therefore, studies are in general small or restricted to individual cases. Despite this challenge recent advances have been made specifically at the molecular level. Molecular alterations such as MAML2 rearrangements in mucoepidermoid carcinoma, MYB rearrangements in adenoid cystic carcinomas, and EWSR1 rearrangements in hyalinizing clear cell carcinomas and myoepithelial tumors have been identified. These molecular alterations might be helpful in the distinction of these salivary gland tumors from other neoplasms in the lung. However, the distinction from metastatic disease remains challenging. Awareness of these tumors and knowledge of available ancillary studies to confirm the diagnosis is important to avoid misdiagnosis which might lead to differences in treatment, management, and prognosis. Further studies are needed to identify biomarkers to better predict patient's outcome and for individual management and treatment of patients.

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.

Molecular Profiling of Salivary Oncocytic Mucoepidermoid Carcinomas Helps to Resolve Differential Diagnostic Dilemma With Low-grade Oncocytic Lesions

Oncocytic mucoepidermoid carcinoma (OMEC) is a rare but diagnostically challenging variant of mucoepidermoid carcinoma (MEC). OMEC is notable for differential diagnostic considerations that are raised as a result of overlap with other benign and low-grade oncocytic salivary gland tumors. Diffuse and strong immunoreactivity of p63 protein may be useful in distinguishing OMEC from its mimics. However, focal p63 staining can be present in benign oncytomas. Presence of mucin-containing cells, mucinous cystic formation, and foci of extravasated mucin are considered a hallmark of MEC. True mucocytes may be, however, very few and hardly discernable in OMECs. Recent evidence has shown that most MECs harbor gene fusions involving MAML2. A retrospective review of archived pathology files and the authors' own files was conducted to search for "low-grade/uncertain oncocytic tumor," "oncocytoma," and "oncocytic carcinoma" in the period from 1996 to 2019. The tumors with IHC positivity for p63 and/or p40, and S100 negativity, irrespective of mucicarmine staining, were tested by next-generation sequencing using fusion-detecting panels to detect MAML2 gene rearrangements. Two index cases from consultation practice (A.S. and A.A.) of purely oncocytic low-grade neoplasms without discernible mucinous cells showed a CRTC1-MAML2 fusion using next-generation sequencing, and were reclassified as OMEC. In total, 22 cases of oncocytic tumors, retrieved from the authors' files, and from the Salivary Gland Tumor Registry, harbored the MAML2 gene rearrangements. Presence of mucocytes, the patterns of p63 and SOX10 immunopositivity, and mucicarmine staining were inconsistent findings. Distinguishing OMEC devoid of true mucinous cells from oncocytoma can be very challenging, but it is critical for proper clinical management. Diffuse and strong positivity for p63 and visualization of hidden mucocytes by mucicarmine staining may be misleading and does not always suffice for correct diagnosis. Our experience suggests that ancillary studies for the detection of MAML2 rearrangement may provide useful evidence in difficult cases.

Molecular and Cellular Modelling of Salivary Gland Tumors Open New Landscapes in Diagnosis and Treatment

Salivary gland tumors are neoplasms affecting the major and minor salivary glands of the oral cavity. Their complex pathological appearance and overlapping morphological features between subtypes, pose major challenges in the identification, classification, and staging of the tumor. Recently developed techniques of three-dimensional culture and organotypic modelling provide useful platforms for the clinical and biological characterization of these malignancies. Additionally, new advances in genetic and molecular screenings allow precise diagnosis and monitoring of tumor progression. Finally, novel therapeutic tools with increased efficiency and accuracy are emerging. In this review, we summarize the most common salivary gland neoplasms and provide an overview of the state-of-the-art tools to model, diagnose, and treat salivary gland tumors.

Oncocytic mucoepidermoid carcinoma (OMEC) of the parotid gland in a 12-year-old patient: A diagnostic challenge on cytology

Mucoepidermoid carcinoma is the most common malignant salivary gland neoplasm comprising approximately 10% of all tumours of the major salivary gland. Owing to a plethora of morphological variations, it poses a diagnostic challenge on fine-needle aspiration cytology. Oncocytic variant of mucoepidermoid carcinoma is a rare subtype seen in the age group of 20-80 years. It is crucial to make the correct diagnosis on cytology as it has therapeutic implications. Oncocytes can be present in a wide range of salivary gland lesions ranging from non-neoplastic conditions to benign and malignant lesions. We report a case of oncocytic mucoepidermoid carcinoma of the parotid gland in a 12-year-old boy which is the youngest age reported for the same. On cytology, this case was initially diagnosed as Warthin's tumour and was supported by radiology. However, histomorphological findings clinched the diagnosis of an oncocytic variant of mucoepidermoid carcinoma with the aid of immunohistochemistry.

Conjunctival 'mucoepidermoid carcinoma' revisited: a revision of terminology, based on morphologic, immunohistochemical and molecular findings of 14 cases, and the 2018 WHO Classification of Tumours of the Eye

In 2018, the consensus meeting for the WHO Classification of Tumours of the Eye decided that conjunctival mucoepidermoid carcinoma should be reclassified as adenosquamous carcinoma, as this represented a better morphological fit. To examine the applicability of this terminology, we studied the clinical, histopathological, immunohistochemical and molecular pathology of 14 cases that were originally diagnosed as conjunctival mucoepidermoid carcinoma. There were 7 (50%) females and 7 (50%) males. The median age was 64 years. The left eye was affected in 8 and the right eye in 6 patients. In-situ carcinoma was present in 11/14 (79%) cases and comprised in-situ squamous cell carcinoma (SCC) and conjunctival intraepithelial neoplasia with mucinous differentiation (CIN-Muc). Invasive carcinoma was present in 11/14 (79%) cases. Group 1 (1/11 cases, 9%) comprised invasive SCC only. Group 2 (6/11 cases, 55%) comprised SCC with mucinous differentiation, manifesting as scattered intracellular mucin, occasionally together with intercellular mucin, with no evidence of true glandular differentiation. Group 3 (3/11 cases. 27%) comprised true adenosquamous carcinoma. Group 4 (1/11 cases, 9%) comprised pure adenocarcinoma. Thirteen of 14 cases (93%) underwent FISH for MAML2 translocation and none were rearranged. Two cases harboured high-risk HPV (type 16 and 18). The combined findings confirm that all lesions in our study were not mucoepidermoid carcinoma, but represented predominantly SCC with mucinous differentiation and adenosquamous carcinoma. We, therefore, recommend future revision of the WHO classification to include SCC with mucinous differentiation alongside adenosquamous carcinoma.

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

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

MAML2 rearrangement as a useful diagnostic marker discriminating between Warthin tumour and Warthin-like mucoepidermoid carcinoma

Warthin tumour is the second most common benign neoplasm of salivary glands. Despite its relatively characteristic histology, it may sometimes mimic other lesions. Here, we report two female non-smoker patients diagnosed with low-grade mucoepidermoid carcinoma with oncocytic epithelium and prominent lymphoid (Warthin-like) stroma and with molecularly confirmed MAML2 rearrangement. In addition, we screened a consecutive series of 114 Warthin tumour cases by means of MAML2 break apart fluorescence in situ hybridization to assess its value in differential diagnosis. MAML2 rearrangement was detected in both mucoepidermoid carcinoma cases, while all Warthin tumours were negative. Taking into account the literature data, Warthin-like mucoepidermoid carcinomas are more frequently observed in women, while a slight male predominance and smoking history are typical for Warthin tumour. In addition, the patients with Warthin-like mucoepidermoid carcinoma were significantly younger than those with Warthin tumour. To conclude, Warthin-like mucoepidermoid carcinoma may usually be suspected based on histology, while the diagnosis can be confirmed by means of molecular assays such as FISH. The investigation of MAML2 status is particularly advised when Warthin tumour is considered in a young, non-smoking, female patient.

Pediatric Warthin-like Mucoepidermoid Carcinoma: Report of Two Cases with One Persistent/Recurrent as Conventional Mucoepidermoid Carcinoma

Mucoepidermoid carcinoma (MEC) is the most common primary salivary gland malignancy. While salivary gland neoplasia is rare in children, MEC is much more likely to occur in the pediatric population than Warthin tumor, a common benign salivary gland neoplasm associated with smoking and older age. The recently-reported Warthin-like variant of MEC bears a striking histologic resemblance to Warthin tumor, representing a potential diagnostic pitfall. Therefore, low-power observation of Warthin-like features in pediatric salivary gland tumors should prompt careful diagnostic consideration of Warthin-like MEC. Two cases of Warthin-like MEC in the parotid glands of teenaged patients were identified in the archives of the Department of Pathology at Children's Medical Center in Dallas, Texas. Surgical material for each case was reviewed and both diagnoses were verified. Fluorescence in situ hybridization (FISH) for CRTC1-MAML2 fusion was performed in both cases. Histologically, neither tumor exhibited the classic bilayer of oncocytic epithelial cells characteristic of Warthin tumor. Instead, the neoplastic epithelial cells exhibited architectural and cytologic atypia, with mucous cells interspersed. CRTC1-MAML2 gene fusions were identified via FISH and confirmed the diagnosis of MEC in both cases. Of note is that the second patient's tumor recurred with features of conventional MEC, indicating the potential for Warthin-like MEC to undergo this morphologic change. The present cases illustrate that Warthin-like MEC, like conventional MEC, may occur in the pediatric population. Pediatric and head and neck pathologists must be aware of this variant's existence and diagnostic criteria to avoid misdiagnosis as benign Warthin tumor.

The significance of mucinous metaplasia in Warthin tumor: a frequent occurrence and potential pitfall

Mucinous metaplasia in Warthin tumor (WT) is a recognized phenomenon. Nevertheless, its presence can create a diagnostic challenge in the distinction from the newly proposed variant of mucoepidermoid carcinoma (MEC), Warthin-like MEC. In this study, we evaluated the significance and diagnostic relevance of mucinous metaplasia in WTs. A total of 30 WTs diagnosed based on resection specimens formed the basis of this retrospective study. Mucicarmine staining was performed to identify mucinous metaplasia, and fluorescence in situ hybridization (FISH) analysis was used to detect MAML2 gene rearrangement. After review, one MAML2 rearranged case was reclassified as Warthin-like MEC as the classic bilayered epithelium in WT was not identified. The diagnosis of WT was confirmed in the remaining 29 cases. Mucinous metaplasia was encountered in 24 WTs (83%), with 14% (4/29) having an abundant amount. We found that mucinous metaplasia correlated with tumor size (p < 0.05). Age and sex distribution were similar in WT cases with or without mucinous metaplasia. In addition, neither the presence of squamous metaplasia nor the time interval between fine-needle aspiration and surgery was related to mucinous metaplasia (p > 0.05). The MAML2 FISH analyses performed in 18 WTs with variable amounts of mucinous metaplasia were negative for rearrangement. In conclusion, mucinous metaplasia is fairly common in WTs and shows a significant correlation with tumor size. Therefore, caution should be taken to avoid overinterpretation of WT with mucinous metaplasia as MEC in cases showing the classic bilayered oncocytic lining epithelium.

Salivary Gland Cancer in the Era of Routine Next-Generation Sequencing

Next-Generation Sequencing (NGS) is being utilized with increasing frequency in the characterization of salivary gland tumours. The potential scenarios which may be encountered by using this technique in routine practice will be outlined in further text by drawing from our own clinical experience. These include oncocytic mucoepidermoid carcinomas with unusual variant morphology (and negative MAML2 fluorescent in-situ hybridization results), a diagnosis of ameloblastoma changed to adenoid cystic carcinoma (due to MYBL1 fusion presence), a salivary duct carcinoma with an ETV6-NTRK3 fusion (otherwise seen in secretory carcinomas) and novel fusion partners such as EWSR1-BEND2 (otherwise seen in pancreatic neuroendocrine carcinomas). As NGS continues to develop and more widespread clinical implementation increases, we must be cognisant of the need for proper interpretation and in some cases verification using a secondary technique, the limitations of this technique, and the ethical dilemmas one faces when encountering a novel fusion.

Ameloblastoma with mucous cells: A clinicopathological, BRAF mutation, and MAML2 rearrangement study

OBJECTIVES

To investigate the clinicopathological features, BRAF V600E mutation, and MAML2 rearrangement of ameloblastoma with mucous cell differentiation.

MATERIALS AND METHODS

Five cases of ameloblastoma with mucous cell differentiation were retrospectively studied. Clinicopathological features, BRAF V600E mutation, and MAML2 rearrangement were analyzed. Follow-up information was available for all cases.

RESULTS

Of five cases, two cases were male and three were female, aged 18-55 years. Four cases were located in the mandible and one case in the maxilla. Histologically, four of the five cases (80%) presented with cystic features and three of the five cases (60%) with varying degrees of squamous metaplasia. The mucous cells were located in the epithelial islands or the luminal aspect of the cystic cavities. The BRAF V600E mutation was found in three of five cases (60%). All the cases showed no MAML2 rearrangement. Two cases were recurrent lesions, and one case had a local recurrence during the follow-up.

CONCLUSIONS

Ameloblastoma with mucous cell differentiation is closely related to the cystic features, squamous metaplasia, and shows a high prevalence of BRAF V600E mutation. The absence of MAML2 rearrangement reveals that ameloblastoma with mucous cell differentiation and central mucoepidermoid carcinoma (MEC) are two distinct tumor entities.

Pathologic grading of mucoepidermoid carcinomas of the salivary gland and its effect on clinicopathologic follow-up: an institutional experience

Mucoepidermoid carcinoma (MEC) is the most common malignant salivary gland tumor. Differences inprognosis can be noted owing to the tumor grade determined using multiple grading schemes (2-tier: low- and high-grade vs. 3-tier: low-, intermediate-, and high-grade). We studied clinicopathologic features of MEC using a 3-tier grading system and retrospectively categorized cytologic diagnoses as per the Milan System for Reporting Salivary Gland Cytopathology (MSRSGC).A total of 69 cases of MEC were identified, and most were seen in the parotid gland. Aggressive clinical behavior was seen in high-grade MEC compared with intermediate- and low-grade MEC. By fluorescence in situ hybridization (FISH) analysis, MAML2 rearrangements were seen in 78% of cases.The MSRSGC subcategorized the majority (63.8%) of MEC as salivary gland neoplasm of uncertain malignant potential, suspicious for malignancy, or malignant. Clustering intermediate- with low-grade cases did not significantly impact the clinical behavior. Both high-grade and oncocytic MEC can be MAML2 FISH negative.

Synchronous Oncocytic Papillary Cystadenoma and Warthin Tumor of the Parotid Gland

Warthin tumor (WT) is the second most common benign salivary gland neoplasm. It is also the most frequent salivary gland tumor to occur synchronously or metachronously with another salivary gland neoplasm, in the same gland or on the other side. Oncocytic papillary cystadenomas (OPCs) are rare neoplasms that are more common in minor salivary gland locations and in women. We describe in detail the case of a 73-year-old male smoker with synchronous OPC and WT of the parotid gland. On microscopy, both tumors resembled each other considerably, with the only difference being that the OPC lacked the tumor-associated lymphoid proliferation characteristic of WT. These findings highlight that OPC bears considerable similarity to WT. While this morphological similarity may lead to misdiagnosis on rare occasions, it does not affect patient management, as clinical behavior of both these tumors is similar.

Thymic Mucoepidermoid Carcinoma: A Systematic Review and Meta-analysis

Thymic mucoepidermoid carcinoma is a rare tumor that remains poorly characterized and a diagnostic challenge. The aim of this review is to characterize this tumor in a larger cohort of patients using all the available cases in the literature. We systematically searched the PubMed and Scopus database for primary thymic mucoepidermoid carcinoma. A total of 24 studies were included in the final analysis. A total of 41 patients were identified; 23 (56.1%) were male and 18 (43.9%) were female. Mean age was 49.8±21.3 years. Mean tumor size was 7.6±3.5 cm. Twenty (66.7%) were low grade and 8 (26.7%) were high grade. In total, 20 (55.6%) patients were treated with surgery alone. Nodal dissection was performed in 4 cases only. Two patients had MAML2 gene rearrangement and 2 were negative. Follow-up time varied from 2 to 93 months. A total of 13 (44.8%) patients died of disease with a median survival of 12 months. There seems to be a bimodal age distribution with peaks between second and third decades of life, and between sixth and eight decades. Lymph node sampling is frequently not performed; however, we recommend performing it, as it may lead to more accurate staging. There is limited data regarding the utility of MAML2 gene rearrangement in the thymic location. Histologic grade and tumor stage/resectability are the main prognostic factors.

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.

Cytopathology approach to rare salivary gland lesions with oncocytic features

Salivary glands located in the head and neck area are known to have different lesions with prominent oncocytic features. Fine needle aspiration is usually the initial approach in the management of these lesions, whether they represent neoplastic or non-neoplastic processes. Owing to the limited material present upon cytopathologic examination, knowledge of variants and subtypes of various oncocytic lesions that can occur in this area is of major importance to provide the most accurate interpretation to the patients and clinicians. In this article, we selected rare lesions of the salivary glands that may exhibit oncocytic changes, and provided a brief discussion of each one of them, with emphasis on challenges in navigating the differential diagnosis that these cases may pose, from the cytopathology standpoint.

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.

Challenges in Minor Salivary Gland Biopsies: A Practical Approach to Problematic Histologic Patterns

Evaluation of minor salivary gland biopsy can be fraught with a wide range of problems, including technical limitations due to the small size and distorted nature of tissue received and interpretive difficulties navigating the considerable morphologic and immunohistochemical overlap between widely disparate entities. As such, common pathologic findings can evoke a perplexing differential diagnosis that encompasses malignant, benign, and non-neoplastic processes. This review will present the diagnostic considerations that arise from four histologic patterns that are frequently encountered on minor salivary gland biopsies: squamous differentiation, tubular and cribriform growth, mucin production, and myxoid stroma. The discussion herein will emphasize practical strategies and priorities for navigating these differential diagnoses in a clinically-relevant and cost-effective manner.

Clear Cell Carcinoma of Salivary Glands Is Frequently p16 Positive: A Pitfall in the Interpretation of Oropharyngeal Biopsies

Clear cell carcinoma (CCC) is a low-grade malignancy that commonly arises in minor salivary glands of the oropharynx and other sites. EWSR1-ATF1 gene fusions seem to be specific for this salivary neoplasm. Testing for EWSR1-ATF1 has expanded the histologic spectrum of CCC. As one important example, many CCCs have a predominantly squamous phenotype with few clear cells, a finding that can cause confusion with squamous cell carcinoma (SqCC). P16 immunohistochemical staining to determine human papillomavirus (HPV) status has become standard practice for all oropharyngeal carcinomas showing squamous differentiation. The purpose of this study was to determine whether this practice could contribute to the difficulty in distinguishing CCC from p16-positive SqCC. The authors' surgical pathology archives were searched for cases of CCC. All cases were evaluated with p16 immunohistochemistry, high-risk HPV RNA in situ hybridization (ISH), and EWSR1 gene break-apart fluorescence ISH. Sixteen CCCs were identified. All harbored an EWSR1 rearrangement. Eleven patients were women and 5 were men. They ranged in age from 30 to 85 years (mean, 58 y). The CCCs arose in the oropharynx (tongue base or tonsil) (n=8, 50%), oral cavity (n=4, 25%), and nasopharynx (n=4, 25%). Each case demonstrated clear cells, but the proportion was highly variable (10% to 90%, mean 48%), with 7 of 16 cases having <50% clear cells. Submitted diagnoses included SqCC (n=3) and mucoepidermoid carcinoma (n=2). Of the 3 patients diagnosed with SqCC, 1 was scheduled to undergo chemoradiation, and 1 had already completed chemoradiation. All 16 CCCs demonstrated p16 staining, with the percentage of p16-positive cells ranging from ≥70% (n=2), 50% to 69% (n=3), and 10% to 49% (n=11). Staining was cytoplasmic and nuclear. All cases were negative for high-risk HPV by RNA ISH. CCCs regularly show squamous features, often lack prominent clear cell changes, frequently arise in the oropharynx, and invariably show p16 staining. These features may cause confusion with SqCC, particularly HPV-related oropharyngeal SqCC. P16 staining is not to be taken as unequivocal evidence of an HPV-related SqCC, even for carcinomas showing squamous differentiation and originating in the oropharynx. Failure to recognize this pitfall could result in overly aggressive treatment of a low-grade carcinoma.

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.

The reliability of MAML2 gene rearrangement in discriminating between histologically similar glandular odontogenic cysts and intraosseous mucoepidermoid carcinomas

OBJECTIVE

MAML2 expression is proven in the majority of mucoepidermoid carcinomas (MECs) arising in salivary glands. MEC can also occur intraosseously (IMEC). Glandular odontogenic cyst (GOC) is an odontogenic cyst with histologic overlap with IMEC. This study aimed to determine the reliability of MAML2 in distinguishing IMEC cases from GOC cases.

STUDY DESIGN

An institutional review board-approved retrospective search of IMEC, GOC, and IMEC with prior history of GOC was performed within the archives of the University of Florida and the University of Alberta Oral Pathology Biopsy Services. Nine cases from 5 patients were selected. Break-apart fluorescent in situ hybridization analysis was performed on 7 cases for the presence of MAML2 rearrangement.

RESULTS

Four cases had negative MAML2 gene rearrangement, and 3 cases had positive MAML2 gene rearrangement.

CONCLUSIONS

Although it can be concluded that the 3 cases with positive translocation for MAML2 were IMECs, the same conclusion could not be drawn for the 4 cases with negative translocation. Whether the cases that were negative for translocation were GOCs with MEC-like islands or were MAML2-negative IMECs could not be ascertained. Therefore, MAML2 rearrangement is not always reliable in differentiating IMECs from GOCs with overlapping histology.

Genomics of mucoepidermoid and adenoid cystic carcinomas

Objective

To report on the current state of the literature on the genetics of mucoepidermoid and adenoid cystic carcinomas of the salivary glands with a focus on genomic screens and recently discovered genetic translocations.

Methods

A PubMed based literature review was performed to query for genetics related basic science and preclinical studies about mucoepidermoid and adenoid cystic carcinomas of the salivary glands.

Results and conclusions

Genetic translocations between CRTC1 and MAML2 in mucoepidermoid carcinoma and between MYB and NFIB in adenoid cystic carcinoma have been recently discovered and have therapeutic implications. Key signaling pathways such as the EGFR pathway in mucoepidermoid carcinoma and the Notch pathway, chromatin regulation, and c‐kit mediated epithelial‐mesenchymal transitions in adenoid cystic carcinoma have recently been elucidated, pointing to possible therapeutic targets in both cancers.

MAML2 Rearrangements in Variant Forms of Mucoepidermoid Carcinoma: Ancillary Diagnostic Testing for the Ciliated and Warthin-like Variants

Mucoepidermoid carcinoma (MEC) is the most common salivary gland malignancy. Recent studies have shown that most MECs harbor gene fusions involving MAML2-an alteration that appears to be specific for MEC, a finding that could be diagnostically useful. While most cases of MEC are histologically straightforward, uncommon variants can cause considerable diagnostic difficulty. We present 2 variants of MEC for which MAML2 studies were crucial in establishing a diagnosis: a previously undescribed ciliated variant, and the recently described Warthin-like variant. All cases of ciliated and Warthin-like MEC were retrieved from the archives of The Johns Hopkins Hospital. Break-apart fluorescence in situ hybridization for MAML2 was performed on all cases. One ciliated MEC and 6 Warthin-like MECs were identified. The ciliated MEC presented as a 4.6 cm cystic lymph node metastasis originating from the tongue base in a 47-year-old woman. The Warthin-like MECs presented as parotid masses ranging in size from 1.2 to 3.3 (mean, 2.7 cm) in 4 women and 2 men. The ciliated MEC consisted of macrocystic spaces punctuated by tubulopapillary proliferations of squamoid cells and ciliated columnar cells. The Warthin-like MECs were comprised of cystic spaces lined by multilayered oncocytic to squamoid cells surrounded by a circumscribed cuff of lymphoid tissue with germinal centers. In these cases, the Warthin-like areas dominated the histologic picture. Conventional MEC, when present, represented a minor tumor component. MAML2 rearrangements were identified in all cases. Warthin-like MEC, and now a ciliated form of MEC, are newly described variants of a common salivary gland carcinoma. Unfamiliarity with these novel forms, unanticipated cellular features (eg, cilia), and morphologic overlap with mundane benign processes (eg, developmental ciliated cysts, Warthin tumor) or other carcinomas (eg, ciliated human papillomavirus-related carcinoma) may render these variants susceptible to misdiagnosis. These unusual variants appear to consistently harbor MAML2 fusions-a finding that establishes a clear link to conventional MEC and provides a valuable adjunct in establishing the diagnosis.

Central mucoepidermoid carcinoma arising from glandular odontogenic cyst confirmed by analysis of MAML2 rearrangement: A case report

Central mucoepidermoid carcinoma (MEC) poses a diagnostic challenge because of its rarity and histological overlap with glandular odontogenic cyst (GOC). In MEC of both salivary glands and jaws, MAML2 arrangement has been well known as the specific gene alteration. We report a case of central MEC arising from GOC diagnosed by MAML2 fusion gene. A 57-year-old male presented a multilocular cystic lesion in left molar region of the mandible. Histopathologically, multiple cysts lined by thin cuboidal or non-keratinized squamous epithelium with small duct-like structures, mucous cells and ciliated cells were present. It was diagnosed as GOC. The recurrent lesion after nine years showed the proliferation of many cystic and solid nests composed of epidermoid, mucous and intermediated cells. Nested PCR revealed CRTC3-MAML2 fusion gene in the recurrent lesion, but not in the primary one. Similarly, MAML-2 rearrangement by FISH analysis was positive in the recurrent lesion, while negative for the primary one, thus confirming the diagnosis of central MEC arising from GOC. Analysis of MAML2 rearrangement can be used as a supportive evidence to distinguish central MEC from GOC.

Warthin Tumor–Like Mucoepidermoid Carcinoma

Mucoepidermoid carcinoma (MEC) shows a wide morphologic spectrum, including epithelium with oncocytic or squamous metaplastic changes overlying a prominent cystic architecture, as well as tumor-associated lymphoid tissue. We illustrate a case of MEC of the parotid in a 17-year-old female, in which all these features occurred extensively, such that they accounted for almost the entire neoplasm, and closely mimicked Warthin tumor histologically. This highlights the need for diagnostic awareness of this particular morphologic variant of MEC, as patients could potentially be inappropriately discharged from follow-up if diagnosed with a benign neoplasm.

Cytological features of the Warthin-like variant of salivary mucoepidermoid carcinoma

Warthin-like mucoepidermoid carcinoma is a recently proposed variant of musoepidermoid carcinoma. Histologically, it is characterized by its close resemblance to Warthin tumor, including dense lymphocytic infiltration, flattened intermediate epithelium resembling squamous metaplasia, and cystic change. Given its histologic similarity to Warthin tumor, confirmatory testing for MAML2 rearrangement is often required for this diagnosis. Here we present the first cytologic reports of two 53-year-old female patients with parotid masses. In both cases, the fine needle aspirations showed fragments of bland epithelium with a squamous appearance, mucinous cyst content, and focal lymphocytic background. Neither frank keratinization nor mucinous cells were identified in the smears. Fluorescence in situ hybridization (FISH) study confirmed MAML2 rearrangement on the resection specimens in both. Other cytologic differential diagnoses, including Warthin tumor with metaplasia, lymphadenoma, and lymphoepithelial cyst, were briefly discussed.