Recurrent RET Gene Rearrangements in Intraductal Carcinomas of Salivary Gland

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.

Targeted RNA sequencing in diagnostically challenging head and neck carcinomas identifies novel MON2::STAT6, NFATC2::NUTM2B, POC5::RAF1, and NSD3::NCOA2 gene fusions

AIMS

Although molecular tests developed for a growing list of oncogenic alterations have significantly aided in the classification of head and neck carcinomas, tumours in which prototypical histologic and immunophenotypic features are lacking or only partially developed continue to pose diagnostic challenges. Searching for known diagnostic and therapeutic targets by clinical next-generation sequencing (NGS) assays can often lead to new discoveries.

METHODS AND RESULTS

We present our institutional experience in applying targeted RNA NGS in 36 head and neck carcinomas that were morphologically difficult to classify between 2016 and 2023. The patients ranged in age from 5 to 83 years (median, 64), with the majority of tumors occurring in the major salivary glands and the sinonasal tract. Overall, seven (19%) cases showed unusual gene rearrangements, including five novel alterations: MON2::STAT6 in a hard palate adenocarcinoma with mucinous features, POC5::RAF1 in apocrine intraductal carcinoma of the lacrimal gland, EWSR1::CDADC1 fusion in a basaloid carcinoma of the submandibular gland, NFATC2::NUTM2B in myoepithelial carcinoma, and NSD3::NCOA2 fusion in a peculiar high-grade carcinoma with a peritheliomatous growth pattern, and focal myogenic differentiation. Potential therapeutic actionability was identified in three cases (RAF1 and FGFR2 fusions).

CONCLUSION

These findings broaden the current spectrum of gene rearrangements in head and neck carcinomas and support the utility of clinical NGS in identifying unusual, actionable alterations in diagnostically challenging cases.

Intraductal carcinoma of the parotid gland, mixed intercalated duct and oncocytic subtype with mucinous and serous acinar differentiation: cytologic and histologic features of a novel morphology

Intraductal carcinoma (IDC) of the salivary gland is rare. Histologic subtypes include intercalated duct, oncocytic, apocrine, and hybrid/mixed. Molecular correlates have been described, with intercalated duct IDC typically harboring NCOA4::RET, while TRIM33::RET, or BRAFV600E pathogenic variants predominating in oncocytic IDC. We describe the case of a 77-year-old female with a parotid mass. Fine needle aspiration showed a population of low-grade epithelial cells with frequent cytoplasmic vacuolization, which were positive for S-100, SOX-10, and mammaglobin, and was interpreted as compatible with secretory carcinoma. A dual cell population was recognized on surgical resection, predominantly oncocytic, with at least one focus prototypical of intercalated IDC. Luminal secretions were positive for mucicarmine, while PAS after diastase highlighted the latter in addition to zymogen-like cytoplasmic granules. RNA sequencing detected a NCOA4::RET fusion. This is the first report of the cyto-histologic features of the mixed intercalated duct and oncocytic subtype IDC with mucous and serous acinar-like differentiation.

Role of Ancillary Techniques in the Differential Diagnosis of Salivary Gland Carcinomas

Paiva-Correia A, Hellquist H, Apolónio J, Castelo-Branco P. Role of ancillary techniques in the differential diagnosis of salivary gland carcinomas. The diagnosis of salivary gland carcinomas (SGC) rests mainly on histology, but immunohistochemical and molecular investigations are often necessary for differential diagnosis. This review is primarily aimed as a tool for pathologists in non-specialised head and neck hospitals who encounter a limited number of SGC annually. The use of testing an initial antibody panel, which may comprise both positive and negative expression for a suspected entity, and examples of different panels are outlined. We also focused on acinic cell carcinoma (AcCC), which is positive for DOG1 and negative for mammaglobin, whilst secretory carcinoma (SC) is positive for mammaglobin and negative for DOG1. In addition, the exclusive expression of androgen and HER2 in salivary duct carcinoma (SDC) and its use for differential diagnosis are also addressed. This review also highlights the particularities of mucoepidermoid carcinoma (MEC) and its negativity for S100 and SOX10, which distinguishes it from some of its mimics. In laboratories with limited access to antibodies for SGC, we recommend inclusion of mammaglobin. The use of molecular techniques for the diagnosis of MEC (MAML2), SC (ETV6), adenoid cystic carcinoma (MYB), and AcCC (NR4A3) is discussed. We highlight the role of commonly available antibodies for the histological classification of SGC.

Intraductal Carcinoma of the Salivary Gland With Extensive Bone Invasion

This case report describes a 77-year-old woman who presented to the oral and maxillofacial surgery department with a palatal mass.

Update of newly-recognized salivary gland neoplasms: molecular and immunohistochemical findings and clinical importance

With the advancement of molecular testing and the routine use of immunohistochemical stains, salivary gland tumours previously categorized as adenoma or adenocarcinoma, not otherwise specified, are being reclassified with distinct diagnoses. Newly recognized benign entities include: sclerosing polycystic adenoma, keratocystoma, intercalated duct hyperplasia and adenoma, and striated duct adenoma. Newly recognized malignant salivary gland tumours include: microsecretory adenocarcinoma, sclerosing microcytic adenocarcinoma, and mucinous adenocarcinoma. Additionally, rare subtypes of mucoepidermoid carcinoma have been described, including Warthin-like and oncocytic. Understanding of intraductal carcinoma continues to evolve. Correctly distinguishing these lesions from mimickers can be crucial for appropriate patient care and prognostication, as well as future conceptualization of salivary disease.

Relative Frequency of Primary Salivary Gland Tumors: Multicenter Study of 796 Cases from Riyadh, Saudi Arabia

Background and Objectives: Salivary gland tumors (SGTs) are diverse lesions with varying morphological and clinical characteristics. Limited data exist on the distribution of SGTs in Saudi Arabia. We aimed to fill this gap by examining the distribution of SGTs across four tertiary hospitals in Riyadh. Materials and Methods: A retrospective analysis was conducted on SGT cases diagnosed from January 2010 to December 2022 to investigate the clinicopathological features (tumor location, patient sex, and age). Histological slides were evaluated by two independent certified oral pathologists and classified based on the latest 2022 World Health Organization classification (WHO). Results: There were 796 SGTs. Most cases occur in individuals in their 4th to 5th decades of life. The parotid gland was the predominant site (79.4%), followed by the submandibular gland (9.3%). More than half of the tumors (527, 66.2%) were benign, involving major and minor salivary glands. Pleomorphic adenoma was the most common benign tumor, accounting for 354 cases (44.5%), followed by Warthin tumor with 117 cases (14.7%). Mucoepidermoid carcinoma was the most prevalent malignant tumor, identified in 98 patients (12.3%). Additionally, 36 (4.5%) mesenchymal and 30 (3.8%) hematolymphoid non-epithelial SGTs were reported. Conclusions: This multicenter study is the largest of its kind in Saudi Arabia, identifying pleomorphic adenoma and mucoepidermoid carcinoma as the most commonly reported benign and malignant tumors, respectively. These findings offer valuable insights into the understanding of salivary gland tumors globally.

Clinicopathological, Prognostic and Molecular Profile of Salivary Gland Intraductal Carcinoma: A Systematic Review

PURPOSE

This study aimed to conduct a systematic review summarizing the clinicopathological, prognostic, and molecular features of salivary gland intraductal carcinoma (SGIC).

METHODS

This study followed the PRISMA 2020 guidelines and was registered in the PROSPERO database. It included case reports, case series studies, and cohort studies of SGIC indexed in the PubMed, Web of Science, Scopus, and Embase databases published between 1983 and 2024. Collected variables underwent descriptive analysis, association analysis using Fisher's tests, and Kaplan-Meier analysis. The quality assessment of the included studies was conducted using the Joanna Briggs Institute tools.

RESULTS

This systematic review yielded 59 studies, comprising 186 SGIC cases. Most of cases involved the parotid gland of male patients around 60 years old. Lesions predominantly exhibited noninvasive growth, an intercalated duct phenotype, and minimal pleomorphism. Most of the patients did not develop recurrent or metastatic disease, indicating a good prognosis. However, male sex, invasive lesions, adjuvant treatments, high-grade lesions, as well as lymph node or distant metastasis negatively affected the survival rates. Overall SGIC cases showed S100, mammaglobin, SOX10, AR, CK7, p63, calponin, CK14, SMA, and p40 positivity and a low Ki67 index. Common molecular alterations included NCOA4-RET, TRIM33-RET, and TRIM27-RET fusions, and HRAS, PIK3CA, and BRAF V600E mutations.

CONCLUSION

SGIC is a histopathologically and molecularly heterogeneous lesion with an overall excellent prognosis. The presence of invasive lesions, as well as lymph node or distant metastasis, has emerged as one of the most critical prognostic factors in SGIC patients.

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.

NanoString nCounter-Based Assay for Detection of Fusion-Associated Salivary Gland Tumors

PURPOSE

Salivary gland tumors include numerous subtypes that vary from benign to highly aggressive, with many showing overlapping histopathological features that can make diagnosis challenging. Most subtypes express driver fusion genes that are tumor specific, and detection of such fusions is useful for differentiating amongst specific diagnoses, determining appropriate tumor grading, and guiding effective treatment. Currently, fusions can be detected by FISH, RT-PCR or through next-generation sequencing approaches, all of which are highly effective methodologies but can be costly or time consuming.

METHODS

We developed a rapid NanoString nCounter platform-based assay to detect salivary gland tumor fusions using a combination of fusion junction-specific probes and an approach through differential exon expression analysis. The assay includes 68 junction-specific probes and analysis of exon expression across 9 fusion-associated genes in a single multiplex assay.

RESULTS

Out of 55 retrospective and 171 prospective cases assayed, we accurately detected the majority of cases of pleomorphic adenoma, adenoid cystic carcinoma, cribriform adenocarcinoma, clear cell carcinoma, secretory carcinoma and NUT-rearranged carcinoma, including cases of these tumor types arising in non-salivary gland sites, with the major drawback being an inability to detect MAML2-containing mucoepidermoid samples. With mucoepidermoid carcinoma excluded, the assay shows an overall sensitivity of 96.1% and specificity of 100%.

CONCLUSION

We show that the majority of salivary gland tumor fusions can be effectively detected with a single rapid NanoString based assay, which can serve as a useful adjunctive tool for routine diagnostic head and neck pathology. The assay is low cost with a rapid turnaround time (30 h total assay time per sample batch, with minimal technician input required) compared to alternate detection methods.

Molecular landscape of salivary gland malignancies. What is already known?

Salivary gland carcinomas (SGCs) are highly heterogeneous histopathological entities that arise in either the major or minor salivary glands. Although uncommon, these tumours exhibit considerable aggressiveness, unpredictable progression, and significant mortality. The fifth edition of the World Health Organisation classification of head and neck tumours distinguishes between 24 salivary gland malignancies. This may lead to difficulties in terms of diagnostic accuracy and suitable therapeutic selection. Mucoepidermoid carcinoma occurs most frequently and is characterised by gradual disease progression. Although salivary duct carcinoma, myoepithelial carcinoma, and carcinoma ex pleomorphic adenoma are rarely detected, they contribute to poor patient outcomes. Currently, attempts have been made to establish molecular characterisation of SGCs to improve differential diagnosis and create targeted treatments. This study aimed to summarise current knowledge regarding genetic variations in the most common salivary gland malignancies.

Bronchial Sialadenoma Papilliferum in a 10-Year-Old Boy

Sialadenoma papilliferum (SP) is a rare salivary gland tumor mostly reported in the oral cavity. Here we describe a bronchial SP in the left upper lobe bronchus of a 10-year-old boy. At bronchoscopy, a well-circumscribed polypoid lesion protruding into the bronchial lumen was identified. The tumor was excised, but eventually, the patient had to undergo a sleeve resection after 2 recurrences. Pathology revealed a papillocystic lesion with exophytic and endophytic components. The cells lining the exophytic surface and papillary structures were columnar and squamous, and the cells lining endophytic cystic and papillary structures were cuboidal to columnar, all of which were diffusely reactive with antibodies to SOX10 protein. The presence of basal cells was demonstrated by p63 immunoreactivity. The cells failed to immunohistochemically express BRAF V600E. Fluorescence in situ hybridization analysis revealed no MAML2 or RET gene rearrangement. The patient is alive 24 years after resection with no additional recurrences. Bronchial SP needs to be recognized and distinguished from other benign and malignant salivary gland and pulmonary neoplasms so that patients can receive appropriate treatment and follow-up.

Pure Apocrine Intraductal Carcinoma of Salivary Glands: Reassessment of Molecular Underpinnings and Behavior

BACKGROUND

Intraductal carcinoma (IDC) of the salivary glands is a confounding entity, our understanding of which continues to evolve. At least four forms have been elucidated based on histomorphology, immunophenotype, and molecular profile: (1) intercalated duct-like, S100/SOX10+ with frequent NCOA4::RET fusions; (2) oncocytic, S100/SOX10+ with TRIM33::RET, NCOA4::RET, and BRAF V600E; (3) apocrine, AR+ with PI3 kinase pathway mutations; and (4) mixed/hybrid intercalated duct-like/apocrine, with S100/SOX10+ and AR+ areas and frequent TRIM27::RET. The revelation that myoepithelial cells harbor the same fusion as luminal cells suggested that fusion-positive cases are not in situ carcinomas as previously believed. To this point, purely apocrine IDC with entirely intraductal growth has not been found to harbor fusions, but very few cases have been tested.

METHODS

IDCs with pure apocrine morphology, entirely intraductal growth, and no precursor lesion (pleomorphic adenoma or sclerosing polycystic adenoma) were retrieved from the authors' archives. Several immunostains (S100, SOX10, GCDFP-15, AR, p40/SMA) and targeted next generation sequencing (NGS) panel including 1425 cancer-related genes were performed.

RESULTS

Seven entirely IDC with pure apocrine type were collected. The cases arose in the parotid glands (mean, 1.9 cm) of 5 men and 2 women ranging from 51 to 84 years (mean, 69.7 years). Histologically, tumors consisted of rounded to angulated ductal cysts lined by epithelial cells with abundant finely granular eosinophilic cytoplasm and large nuclei with prominent nucleoli. Pleomorphism was mild to moderate, the mitotic rate was low, and necrosis was absent. Conventionally invasive foci or areas of intercalated duct-like morphology were not identified. In all cases, luminal cells were diffusely positive for AR and GCDFP-15 while negative for S100/SOX10, and the ducts were completely surrounded by myoepithelial cells highlighted by p40 and SMA. Molecular analysis was successful in 6 cases. Three harbored fusions: one with NCOA4::RET, another with STRN::ALK and one with both CDKN2A::CNTRL and TANC1::YY1AP1. The three fusion-negative cases all harbored HRAS mutations; additional mutations (PIK3CA, SPEN, ATM) were found in 2 of 3 cases. All patients were treated by surgery alone. Six of them are currently free of disease (follow up 12-190 months), but the case harboring NCOA4::RET developed lymph nodes metastasis in the form of a fusion-positive invasive salivary duct carcinoma.

CONCLUSIONS

Purely apocrine IDC is a heterogeneous disease. A subset seems to be genetically similar to salivary duct carcinoma and may indeed represent carcinoma in situ. The other group harbors fusions, similar to other forms of IDC. Moreover, the occurrence of lymph node metastasis discredits the idea that any fusion-positive IDC with a complete myoepithelial cell layer has no metastatic potential. With the wide use of RET-and ALK-based targeted therapies, our findings further underscore the importance of fusion analysis for IDC.

Characterization of a Molecularly Distinct Subset of Oncocytic Pleomorphic Adenomas/Myoepitheliomas Harboring Recurrent ZBTB47-AS1::PLAG1 Gene Fusion

Recurrent gene fusions are common in salivary gland tumors including benign tumors, such as pleomorphic adenoma (PA) and myoepithelioma (ME). In cases where chromosomal rearrangement is identified in the pleomorphic adenoma gene 1 (PLAG1) gene, different gene partners are found. Oncocytic metaplasia, characterized by oncocytes with abundant eosinophilic granular cytoplasm and hyperchromatic nuclei, is a well-known phenomenon in salivary gland neoplasms. However, the pure oncocytic variant of PA/ME showed PLAG1 gene rearrangements involving various gene partners at the molecular level, without any recurrent fusion being found. Our study includes 20 cases of PA/ME, with 11 females and 9 males. The age of patients ranged from 37 to 96 years, with a median age of 62.8 years. Most tumors originate from the parotid gland. The median size of the tumor was 26.5 mm (range: 13 to 60 mm). Among the 20 cases, 14 were a pure oncocytic variant of PA/ME, whereas 6 cases showed focal oncocytic or oncocytic-like aspects. Molecular studies on 20 cases of PA/ME were conducted. A novel recurrent ZBTB47-AS1::PLAG1 fusion was identified in 6 of 12 cases with pure oncocytic metaplasia, whereas the other cases had PLAG1 gene fusion with different gene partners. The transcriptomic analysis of the cases harboring ZBTB47-AS1::PLAG1 fusion demonstrated that these tumors have a distinct molecular profile from conventional PA/ME. This study reveals a unique subset in the oncocytic PA/ME spectrum characterized by pure oncocytic morphology with larger oncocytic cells and recurrent ZBTB47-AS1::PLAG1 fusion. It also highlights the transcriptomic distinctness of salivary gland adenomas with pure oncocytic metaplasia in the spectrum of salivary gland neoplasms. Further studies are needed to better understand the oncocytic variant of PA/ME and to determine the true nature of oncocytic cells in PA/ME.

Oncocytoid Salivary Tumors: Differential Diagnosis and Utility of Newly Described Immunohistochemistry

BACKGROUND

Oncocytoid salivary tumors include several entities such as oncocytoma, Warthin tumor, secretory carcinoma (SC), salivary duct carcinoma (SDC), acinic cell carcinoma (AciCC), oncocytic mucoepidermoid carcinoma (OMEC), intraductal carcinoma, and epithelial myoepithelial carcinoma (EMC). This review investigates the differential diagnosis of oncocytoid salivary tumors and explore the role of newly described immunostains as valuable tools for their diagnosing and potentially guiding treatment options.

METHODS

We assess the utility of incorporating new immunohistochemical markers in routine practice to aid in diagnosing oncocytoid salivary tumors and potentially provide treatment options.

RESULTS

In SDC, AR and Her2 immunostains are utilized as diagnostic tools and biomarkers for selecting patients who might benefit from Androgen-deprivation therapy (ADT) and HER2-targeted therapy. Furthermore, nuclear Pan-Trk immunostaining can aid in diagnosing SC. Additionally, NR4A3 immunostaining has been shown high sensitivity and specificity in identifying AciCC in both surgical and cytologic specimens. Similarly, RAS Q61R mutant-specific immunostaining, detected in EMC, may offer a cost-effective diagnostic marker for this tumor. Although further studies are required to evaluate the role of BSND, this marker has been reported to be positive in Warthin tumor and oncocytoma, aiding in differentiating them from other oncocytoid tumors, particularly OMEC. In addition, BRAFV600E mutant-specific immunostaining can serve as a diagnostic and potentially therapeutic marker for oncocytic intraductal carcinoma in mutation positive cases.

CONCLUSION

Oncocytoid salivary tumors may have overlapping morphologies, posing diagnostic challenges for pathologists. Recently described immunohistochemical markers may offer valuable tools for diagnosing and potentially guiding treatment options for these tumors.

Current management and future challenges in salivary glands cancer

Salivary gland cancers (SGCs) are rare, accounting for less than 5% of all malignancies of the head and neck region, and are morphologically heterogeneous. The diagnosis is mainly based on histology, with the complementary aid of molecular profiling, which is helpful in recognizing some poorly differentiated, borderline, or atypical lesions. Instrumental imaging defines the diagnosis, representing a remarkable tool in the treatment plan. Ultrasound and magnetic resonance are the most common procedures used to describe the primary tumour. The treatment of SGCs is multimodal and consists of surgery, radiotherapy, and systemic therapy; each treatment plan is, however, featured on the patient and disease's characteristics. On 24 June 2022, in the meeting "Current management and future challenges in salivary gland cancers" many experts in this field discussed the state of the art of SGCs research, the future challenges and developments. After the meeting, the same pool of experts maintained close contact to keep these data further updated in the conference proceedings presented here. This review collects the insights and suggestions that emerged from the discussion during and after the meeting per se.

Clinicopathological profile of sclerosing polycystic adenoma/adenosis: A systematic review

In this systematic review, we aimed to evaluate the clinicopathological profile of sclerosing polycystic adenoma (SPA). PubMed, Scopus, EMBASE, Lilacs, Web of Science, and gray literature were searched to access cases of SPA in salivary glands. One hundred and thirty cases of SPA were found across 61 selected articles. SPA affected mainly the parotid gland of adults with a mean age of 44.6 years old, with a slight preference for females. The lesion was usually presented as a painless firm mass with a long period of evolution. Histologically, they are well-delimitated lesions composed of acinar and ductal elements with a variety of cytomorphologic features surrounded by a densely collagenized stroma. PI3K was the most common gene mutation related to SPA. SPA is a benign condition that mainly affects the parotid gland of female patients and it is usually treated by surgical resection with a good prognosis.

Salivary gland neoplasms in small biopsies and fine needle aspirations

Salivary gland neoplasms are rare and represent a diverse group of head and neck tumors. Their diagnosis in limited cellularity specimens can be challenging as many of these have overlapping clinical, radiological presentation, and pathologic features. Fine needle aspiration and/or core biopsies are more of a norm than rarity to be performed preoperatively to provide invaluable information that can guide clinical management including surgery. Even though these limited specimens may not always provide a definitive diagnosis; they have high sensitivity in confirming primary neoplasia, assessing the tumor grade, and ruling out non-surgical disease. An algorithmic pattern based approach can help narrow the differential diagnosis; leading to a definitive diagnosis with the help of specific ancillary studies.

Salivary Gland-like Tumors of the Breast

CONTEXT

The World Health Organization classification of tumors of the breast recognizes several special type carcinomas and benign lesions with features comparable to those of salivary gland tumors.

OBJECTIVE

To discuss the histologic, immunophenotypic, molecular, and clinical features of salivary gland-like carcinomas of the breast. These breast tumors are often negative for hormone receptors and human epidermal growth factor receptor 2 (HER2), that is, triple-negative, but they generally have a much better prognosis than triple-negative breast carcinomas of no special type. We compare the immunophenotypic, molecular, and clinical features of these breast tumors with their salivary gland counterparts, highlighting similarities and differences. We also discuss benign salivary gland-like breast tumors. Finally, we highlight recent developments in understanding the molecular pathogenesis of these breast tumors and novel ancillary studies that can be used to support their diagnosis.

DATA SOURCES

A literature review was conducted, and papers were selected for further analysis and discussion by the authors of this review based on their novelty, applicability, and impact in the field.

CONCLUSIONS

Breast tumors that exhibit morphologic overlap with salivary gland tumors have been recognized by pathologists for decades, but the similarities and differences in their molecular pathogenesis have not been understood until more recently. These developments have led to novel diagnostic tools and further knowledge of these rare breast lesions.

RET-Altered Cancers-A Tumor-Agnostic Review of Biology, Diagnosis and Targeted Therapy Activity

RET alterations, such as fusions or mutations, drive the growth of multiple tumor types. These alterations are found in canonical (lung and thyroid) and non-canonical (e.g., gastrointestinal, breast, gynecological, genitourinary, histiocytic) cancers. RET alterations are best identified via comprehensive next-generation sequencing, preferably with DNA and RNA interrogation for fusions. Targeted therapies for RET-dependent cancers have evolved from older multikinase inhibitors to selective inhibitors of RET such as selpercatinib and pralsetinib. Prospective basket trials and retrospective reports have demonstrated the activity of these drugs in a wide variety of RET-altered cancers, notably those with RET fusions. This paved the way for the first tumor-agnostic selective RET inhibitor US FDA approval in 2022. Acquired resistance to RET kinase inhibitors can take the form of acquired resistance mutations (e.g., RET G810X) or bypass alterations.

[New information about tumours of the salivary glands : WHO classification 2022]

The WHO 2022 classification of head and neck tumours contains another slight increase in the number of listed benign and malignant tumour entities of the salivary glands. This includes conceptual changes and alterations in the terminology of some entities. While some new features are regarded as preliminary or provisional, others are strongly disputed (for example the terminology of intraductal carcinoma). The impact of molecular findings, mainly recurrent gene fusions, continues to increase rapidly and some have been included in the definition of certain tumour entities. The significance of molecular findings is, however, still largely restricted to diagnostic aspects. Newly included entities include microsecretory carcinoma (defined by an SS18::MEF2C fusion), sclerosing microcystic adenocarcinoma (similar to skin adnexal tumours of the same name) and mucinous adenocarcinoma (characterized by AKT1 mutations with heterogeneous morphology).

Proceedings of the North American Society of Head and Neck Pathology Companion Meeting, New Orleans, LA, March 12, 2023: Classification of Salivary Gland Tumors: Remaining Controversial Issues?

The salivary gland section in the 5th edition of the World Health Organization Classification of Head and Neck Tumours includes a description of several new entities. In addition, numerous tumor variants were described and new concepts proposed, most of which have been based on recent molecular discoveries. However, there are still some controversial issues that remain to be resolved, and some of them are discussed in this review.

[Primary salivary gland tumors from a pathology perspective : Morphomolecular peculiarities and diagnostic and therapeutic challenges]

Similar to tumors of other organs, salivary gland neoplasms were historically viewed as a single neoplastic entity and mostly treated as such. Accordingly, only the clinical tumor stage, and not the histological subtype, was considered to be of significant prognostic impact. However, over the years, several distinct sub-entities have been characterized based on morphological features, such as adenoid cystic carcinoma, mucoepidermoid carcinoma, acinic cell carcinoma, and salivary duct carcinoma. Most importantly, the nosology of salivary gland carcinomas has undergone a dynamic "splitting" on the basis of morphological, immunophenotypic, and molecular characteristics, so that 21 independent carcinomas are now listed in the current World Health Organization (WHO) classification. Moreover, it has become evident that splitting of these carcinoma subtypes no longer represents a "pathologist's hobby," but carries significant prognostic and therapeutic relevance for optimized cancer surgery and potentially systemic therapy. The current review summarizes the major features of salivary gland tumors, both benign and malignant, and gives an account of their classification systems and genetic profiles.

RET signaling in breast cancer therapeutic resistance and metastasis

RET, a single-pass receptor tyrosine kinase encoded on human chromosome 10, is well known to the field of developmental biology for its role in the ontogenesis of the central and enteric nervous systems and the kidney. In adults, RET alterations have been characterized as drivers of non-small cell lung cancer and multiple neuroendocrine neoplasms. In breast cancer, RET signaling networks have been shown to influence diverse functions including tumor development, metastasis, and therapeutic resistance. While RET is known to drive the development and progression of multiple solid tumors, therapeutic agents selectively targeting RET are relatively new, though multiple multi-kinase inhibitors have shown promise as RET inhibitors in the past; further, RET has been historically neglected as a potential therapeutic co-target in endocrine-refractory breast cancers despite mounting evidence for a key pathologic role and repeated description of a bi-directional relationship with the estrogen receptor, the principal driver of most breast tumors. Additionally, the recent discovery of RET enrichment in breast cancer brain metastases suggests a role for RET inhibition specific to advanced disease. This review assesses the status of research on RET in breast cancer and evaluates the therapeutic potential of RET-selective kinase inhibitors across major breast cancer subtypes.

Salivary Gland Intraductal Carcinoma: How Do 183 Reported Cases Fit Into a Developing Classification

Salivary gland intraductal carcinoma (IDC) is a very uncommon group of neoplasms. Many names, variations in diagnostic criteria, and newly observed molecular findings (including NCOA4 :: RET , TRIM27 :: RET , HRAS point mutations, and PIK3CA pathway alterations) have generated further confusion in being able to recognize and categorize this group of tumors. Different histologic appearances and patterns of growth suggest there is more than one tumor category, with intercalated duct, apocrine, oncocytic, and hybrid features seen. Frankly destructive invasion further complicates the category, as the name "intraductal" would suggest an "in situ" neoplasm. Recent evidence on fusion-positive IDC demonstrates the same molecular underpinnings in both the ductal and the myoepithelial cells, which aids in further separating these tumors. This article summarizes the historical group of 183 neoplasms classified under the umbrella of IDC and highlights the unique histologic, immunohistochemistry, and molecular features that may further guide nomenclature standardization and harmonization.

Microcribriform Adenocarcinoma of Salivary Glands: A Unique Tumor Entity Characterized by an SS18::ZBTB7A Fusion

The landscape of salivary gland carcinomas is ever-changing, with a growing list of new tumors and newly elucidated variants of well-known tumor entities. The routine use of next-generation sequencing has been instrumental in identifying novel fusions and tumor entities, which has helped bring the classification to a more objective and evidenced-based model. However, morphology remains critical in assessing the validity of these novel molecular findings, and most importantly, in assessing which of these findings will have an impact on the prognosis and treatment decisions for patients. The recognition of microsecretory adenocarcinoma (MSA) as a distinct low-grade malignancy of salivary glands, underpinned by MEF2C::SS18 , and a single possibly related case of SS18::ZBTB7A , recently expanded this growing list of distinctive tumors. It was not until now, however, that the morphology of the latter case was known to be unique and reproducible. The authors have now seen 4 of these distinctive tumors that show a combination of distinctive oncocytic cells forming compact glandular growth as well as amphophilic cells forming tubular growth, and suggest the appellation "microcribriform adenocarcinoma" (MCA). So far, these tumors appear to preferentially occur in nonoral sites (2 parotid, 1 submandibular gland, and 1 bronchial seromucous glands). By immunohistochemistry, they express S100 and SOX-10 with focal outer myoepithelial cells marked by circumferential p63, p40, and smooth muscle actin staining around some of the nests and tubules. The tumors show infiltrative growth within a hyalinized and myxoid stroma. Cytologically, they appear generally low grade, similar to MSA. The morphologic and molecular uniformity of these 4 microcribriform adenocarcinoma cases warrants their recognition, and while related to MSA, they are sufficiently different to be classified as a distinct tumor. So far, in limited follow-up, these tumors appear to be relatively indolent.

PIK3R1, HRAS and AR Gene Alterations Associated with Sclerosing Polycystic Adenoma of the Parotid Gland

Sclerosing polycystic adenoma (SPA) is a rare neoplasm occurring in the salivary glands, mainly the parotid gland. Although it was originally thought to represent a non-neoplastic process, recent genetic data have proven its monoclonality, supporting its neoplastic origin. We report a case of a 73-year-old woman who presented with left neck swelling and pain. A 3 cm hypoechoic, heterogeneous, solid mass was identified on neck ultrasonography within the left parotid gland. Fine needle aspiration revealed benign acinar cells and lymphocytes. Left partial superficial parotidectomy was performed and a diagnosis of SPA was made. Targeted next-generation sequencing (NGS) revealed three clinically significant alterations in the PIK3R1, HRAS, and AR genes. Alterations in the PIK3R1 gene have been previously reported in cases of SPA; however, this study is the first to report two novel clinically significant genomic alterations in the HRAS and AR genes. AR protein expression by immunohistochemistry was strongly and diffusely positive in the neoplastic epithelial cells compared to the adjacent normal salivary gland tissue, which was dead negative for AR. This molecular profile will enhance our understanding of the molecular pathways underlying the development of this tumor. Although this entity was initially thought to be a reactive process, evidence from our case and similar cases strongly support the notion that it is neoplastic due to the presence of specific genetic alterations linked to it.

Bronchial salivary gland–type intraductal carcinoma with KIAA1217::RET gene fusion composed of intercalated and oncocytic components

Salivary gland-type intraductal carcinoma (IC) is a rare malignant salivary gland neoplasm. Primary salivary gland-type IC has never been described in the lung. Herein, we present a primary pulmonary IC in a 63-year-old woman. The tumor originated in the bronchus wall of the right middle lobe. The tumor consisted of two histological types, intercalated component and oncocytic component. The intercalated component showed tubular/cystic pattern composed of column to cube-shaped cells and scattered mucous cells. The oncocytic component showed solid nests composed of large cells with abundant eosinophilic granular cytoplasm. Immunohistochemically, both histological components were positive for cytokeratin 7 (CK7), S-100 protein, SOX10, and mammaglobin. The rimming myoepithelial cells were highlighted by p63 and smooth muscle actin (SMA). The tumor cells were negative for androgen receptor (AR), HER-2, Dog-1, TTF-1, napsin A, GCDFP-15, and GATA3. In the present case, we detected KIAA1217::RET fusion via DNA-based next-generation sequencing (NGS) and RT-PCR, which established the diagnosis of IC at a molecular level. The present case expands the categories of bronchopulmonary salivary gland-type tumors.

RET signaling pathway and RET inhibitors in human cancer

Rearranged during transfection (RET) receptor tyrosine kinase was first identified over thirty years ago as a novel transforming gene. Since its discovery and subsequent pathway characterization, RET alterations have been identified in numerous cancer types and are most prevalent in thyroid carcinomas and non-small cell lung cancer (NSCLC). In other tumor types such as breast cancer and salivary gland carcinomas, RET alterations can be found at lower frequencies. Aberrant RET activity is associated with poor prognosis of thyroid and lung carcinoma patients, and is strongly correlated with increased risk of distant metastases. RET aberrations encompass a variety of genomic or proteomic alterations, most of which confer constitutive activation of RET. Activating RET alterations, such as point mutations or gene fusions, enhance activity of signaling pathways downstream of RET, namely PI3K/AKT, RAS/RAF, MAPK, and PLCγ pathways, to promote cell proliferation, growth, and survival. Given the important role that mutant RET plays in metastatic cancers, significant efforts have been made in developing inhibitors against RET kinase activity. These efforts have led to FDA approval of Selpercatinib and Pralsetinib for NSCLC, as well as, additional selective RET inhibitors in preclinical and clinical testing. This review covers the current biological understanding of RET signaling, the impact of RET hyperactivity on tumor progression in multiple tumor types, and RET inhibitors with promising preclinical and clinical efficacy.

Sclerosing Polycystic Adenoma: Conclusive Clinical and Molecular Evidence of Its Neoplastic Nature

Sclerosing polycystic adenosis, initially considered a non-neoplastic salivary gland lesion and classified as such in the 2017 WHO Classification of Head and Neck Tumors, has been the subject of controversy regarding its possible neoplastic nature. The reporting of recurrent PI3K pathway alteration represents evidence to support these lesions as being neoplastic and more appropriately referred to as sclerosing polycystic adenoma (SPA). Herein, we provide additional evidence that supports the classification of SPA as a true neoplasm. Eight cases of SPA were identified in our database and consultation files. All cases were subjected to PTEN immunohistochemistry (IHC) and next-generation sequencing (NGS). In addition, one patient underwent genetic counseling and germline testing. The cases included 5 men and 3 women with a mean age of 41 years (range 11-78) and all tumors arose in the parotid gland. One patient had multiple recurrences over a period of 2 years. Morphologically the tumors were circumscribed and characterized by an admixture of acini, ducts and cysts embedded in a fibrotic/sclerotic stroma. The cells lining the ducts and cysts showed variable granular, vacuolated, foamy and apocrine cytoplasmic features, as well as acinar cells contained intracytoplasmic brightly eosinophilic granules. The apocrine intraductal proliferations showed mild to moderate atypia in 6 cases. One case showed overt malignant morphology that ranged from intraductal carcinoma to invasive salivary duct carcinoma. Seven cases tested for PTEN IHC showed loss of nuclear expression in the acinar and ductal cells with retained PTEN expression in the myoepithelial cell and stroma. NGS detected PIK3CA or PIK3R1 genetic alterations in 7 cases, including a novel TFG-PIK3CA fusion. Coexisting PTEN mutations were seen in 4 cases, including in a patient with clinical stigmata of Cowden syndrome and confirmed by germline genetic testing. Our findings herein documented including recurrence of tumor, malignant transformation, high prevalence of PI3K pathway oncogenic alterations and the possible heretofore undescribed association with Cowden syndrome add support to classifying SPA as true neoplasms justifying their designation as adenoma, rather than adenosis.

The evolving role of molecular pathology in the diagnosis of salivary gland tumours with potential pitfalls

Salivary gland tumors are diagnostically challenging owing to the morphological diversity within any tumor type and overlapping histomorphology and immunohistochemistry amongst different tumours. In past two decades, rapid progress has been made in the field of understanding the pathogenesis of these tumours with the discovery of many tumour specific translocations and rearrangements. This includes CRTC1-MAML2 and CRTC-MAML2 in mucoepidermoid carcinoma, MYBNFIB and MYBL1-NFIB fusions in adenoid cystic carcinoma, PLAG1 and HMGA2 in pleomorphic adenoma, ETV6-NTRK3 in secretory carcinoma, NR4A3 rearrangements in acinic cell carcinoma, PRKD1 mutations in polymorphous adenocarcinoma and EWSR1-ATF1 in clear cell carcinoma. This review is a lens for progress made till date in the molecular pathology of salivary gland tumours with a special focus on their role as diagnostic tools and implications on clinical management of the patient as prognostic and predictive markers.

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.

Update from the 5th Edition of the World Health Organization Classification of Head and Neck Tumors: Salivary Glands

The salivary gland section in the 5th edition of the World Health Organization Classification of Head and Neck Tumours features a description and inclusion of several new entities, including sclerosing polycystic adenoma, keratocystoma, intercalated duct adenoma, and striated duct adenoma among the benign neoplasms; and microsecretory adenocarcinoma and sclerosing microcystic adenocarcinoma as the new malignant entities. The new entry also includes mucinous adenocarcinoma subdivided into papillary, colloid, signet ring, and mixed subtypes with recurrent AKT1 E17K mutations across patterns suggesting that mucin-producing salivary adenocarcinomas represent a histologically diverse single entity that may be related to salivary intraductal papillary mucinous neoplasm (IPMN). Importantly, the number of entities in the salivary chapter has been reduced by omitting tumors or lesions if they do not occur exclusively or predominantly in salivary glands, including hemangioma, lipoma, nodular fasciitis and hematolymphoid tumors. They are now discussed in detail elsewhere in the book. Cribriform adenocarcinoma of salivary gland origin (CASG) now represents a distinctive subtype of polymorphous adenocarcinoma (PAC). PAC is defined as a clinically, histologically and molecularly heterogeneous disease group. Whether CASG is a different diagnostic category or a variant of PAC is still controversial. Poorly differentiated carcinomas and oncocytic carcinomas are discussed in the category "Salivary carcinoma not otherwise specified (NOS) and emerging entities". New defining genomic alterations have been characterized in many salivary gland 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. The recurrent molecular alterations were included in the definition of mucoepidermoid carcinoma, adenoid cystic carcinoma, secretory carcinoma, polymorphous adenocarcinoma, hyalinizing clear cell carcinoma, mucinous adenocarcinoma, and microsecretory adenocarcinoma.

Sclerosing Polycystic Adenoma of Salivary Glands: A Novel Neoplasm Characterized by PI3K-AKT Pathway Alterations-New Insights Into a Challenging Entity

Sclerosing polycystic adenoma (SPA) is a rare salivary gland neoplasm originally thought to represent a non-neoplastic lesion. Recently we have encountered an index case of apocrine intraductal carcinoma of parotid gland of 62-year-old man with invasive salivary duct carcinoma component arising from SPA, a combination of tumor entities that has never been published so far. Here, we further explore the nature of SPA by evaluating 36 cases that were identified from the authors' consultation files. The patients were 25 females and 11 males aged 11 to 79 years (mean, 47.8 y). All tumors originated from the parotid gland. Their size ranged from 11 to 70 mm (mean, 28 mm). Histologically, all cases revealed characteristic features of SPA, such as lobulated well-circumscribed growth, focal hyalinized sclerosis, presence of large acinar cells with abundant brightly eosinophilic intracytoplasmic granules, and ductal components with variable cytomorphologic characteristics, including foamy, vacuolated, apocrine, mucous, clear/ballooned, squamous, columnar and oncocyte-like cells. In all cases, there were foci of intraluminal solid and cribriform intercalated duct-like epithelial proliferations with variable dysplasia which were positive for S100 protein and SOX10, and fully enveloped by an intact layer of myoepithelial cells. In addition, 14/36 cases (39%) had focal intraductal cribriform and micropapillary apocrine-type dysplastic epithelial structures composed of cells positive for androgen receptors and negative for S100/SOX10. The intraductal proliferations of both types showed focal mild to severe dysplasia in 17 cases (17/36; 47%). Two cases showed overt malignant morphology ranging from high-grade intraductal carcinoma to invasive carcinoma with an apocrine ductal phenotype. Next generation sequencing using ArcherDX panel targeting RNA of 36 pan-cancer-related genes and/or a TruSight Oncology 170/500 Kit targeting a selection of DNA from 523 genes and RNA from 55 genes was performed. Tumor tissue was available for molecular analysis in 11 cases, and 9 (9/11; 82%) of them harbored genetic alterations in the PI3K pathway. Targeted sequencing revealed HRAS mutations c.37G>C, p.(Gly13Arg) (2 cases) and c.182A>G, p.(Gln61Arg) (2 cases), and PIK3CA mutations c.3140A>G, p.(His1047Arg) (3 cases), c.1633G>A, p.(Glu545Lys) (1 case), and c.1624G>A, p.(Glu542Lys) (1 case). Moreover, mutations in AKT1 c.49G>A, p.(Glu17Lys) and c.51dup, p.(Tyr18ValfsTer15); c.49_50delinsAG, p.(Glu17Arg) (as a double hit) were found (2 cases). In addition, germinal and somatic mutation of PTEN c.1003C>T, p.(Arg335Ter); c.445C>T, p.(Gln149Ter), respectively, were detected. Gene fusions were absent in all cases. These prevalent molecular alterations converging on one major cancer-related pathway support the notion that SPA is a true neoplasm with a significant potential to develop intraluminal epithelial proliferation with apocrine and/or intercalated duct-like phenotype. The name SPA more correctly reflects the true neoplastic nature of this enigmatic lesion.

Mutational and immunologic Landscape in malignant Salivary Gland Tumors harbor the potential for novel therapeutic strategies

Salivary gland carcinomas (SGC) are rare (3-6 % of all head and neck cancers) and show biological heterogeneity depending on the respective histological subtype. While complete surgical resection is the standard treatment for localized disease, chemotherapy or radiation therapy are frequently insufficient for the treatment of unresectable or metastasized SGC. Therefore, new therapeutic approaches such as molecularly targeted therapy or the application of immune checkpoint inhibition enhance the treatment repertoire. Accordingly, comprehensive analyses of the genomic landscape and the tumor-microenvironment (TME) are of crucial importance in order to optimize and individualize SGC treatment. This manuscript combines the current scientific knowledge of the composition of the mutational landscape and the TME in SGCs harboring the potential for novel (immune-) targeted therapeutic strategies.

Frankly Invasive Carcinoma Ex-intraductal Carcinoma: Expanding on an Emerging and Perplexing Concept in Salivary Gland Tumor Pathology

Intraductal carcinoma (IDC) of the salivary glands is an uncommon and enigmatic tumor, our understanding of which is rapidly evolving. Recent studies have demonstrated multiple IDC subtypes and consistent gene fusions, most frequently involving RET. Because IDC is a ductal proliferation surrounded by flattened myoepithelial cells, it was previously presumed to be analogous to breast ductal carcinoma in situ, but recent evidence has shown that the myoepithelial cells of fusion-positive IDC harbor the same genetic alterations of the ductal cells and are therefore neoplastic. In addition, there are rare reports of fusion-positive IDC with overt areas of irregular invasion lacking myoepithelial cells, but this phenomenon is not well documented or understood. This study aims to better characterize these frankly invasive carcinoma ex-IDC. All cases of frankly invasive carcinoma ex-IDC were obtained from the authors' files. Inclusion criteria included a component of concurrent or antecedent IDC and/or a fusion known to be associated with IDC. Immunohistochemistry (S100, SOX10, mammaglobin, androgen receptor, p63, p40) and molecular analysis (targeted RNA sequencing or large panel DNA next generation sequencing) was performed. Clinical follow-up was obtained from medical records. Ten cases of frankly invasive carcinoma ex-IDC were identified. The tumors occurred in 8 men and 2 women ranging from 33 to 82 years (mean, 66.3). All but one case arose in the parotid gland. In 4 cases, the IDC component was intercalated duct type. It was mixed apocrine/intercalated duct in two, and in the remaining 4 cases, no residual IDC was identified. The frankly invasive carcinomas were remarkably heterogeneous, ranging from minimally to widely invasive beyond the confines of the IDC, low-grade to high-grade, with morphologies that varied from duct-forming to those having clear cell or sarcomatoid features, to frankly apocrine. The original diagnoses for these cases were (adeno) carcinoma, not otherwise specified (n = 6), salivary duct carcinoma (n = 3), and secretory carcinoma (n = 1). All cases harbored fusions: NCOA4::RET (n = 6), TRIM33::RET (n = 2), TRIM27::RET (n = 1), and STRN::ALK (n = 1). Clinically, one tumor recurred locally, cervical lymph node metastases occurred in five patients, and distant metastasis later developed in four of these patients. Our findings highlight striking diversity in frankly invasive carcinomas that arise from fusion-positive IDC, a tumor which may serve as a precursor neoplasm like pleomorphic adenoma. These carcinomas vary in their extent of invasion, grade, histologic appearances, and clinical behavior. Importantly, in contrast to pure IDC, which is believed to be indolent, many frankly invasive cases were aggressive. Because RET and ALK fusions are targetable, it is important to recognize the broad spectrum of frankly invasive carcinomas that can arise from IDC, particularly because some cases are completely overrun or recur without any recognizable IDC component. These results suggest fusion analysis may be of clinical benefit on any salivary gland (adeno) carcinoma, not otherwise specified or salivary duct carcinoma.

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.

Mammary analogue secretory carcinoma: A challenging case arising in a young man with radiation exposure

Mammary Analogue Secretory Carcinoma (MASC) is a recently described salivary gland tumor frequently sampled via fine-needle aspiration. The cytologic features of MASC are not entirely distinctive and can simulate acinic cell carcinoma, but the tumor harbors an ETV6 gene rearrangement resulting in an ETV6-NTRK3 fusion gene. We present a case of MASC arising in a 31 year old man with a history of multiple radio-embolization procedures.

Practical immunohistochemistry in the classification of salivary gland neoplasms

Diagnosis of salivary gland neoplasms can be challenging for surgical pathologists due to low incidence of tumors as well as overlapping histologic features. On small biopsy, the most important information to be conveyed for clinical management is the distinction between a benign/low grade tumor and a high grade carcinoma. This review will discuss the differential diagnosis of salivary gland tumors based on four broad morphologic patterns: basaloid/tubular/cribriform, (micro)cystic/secretory/mucinous, solid-nested/clear-spindled, and oncocytic/oncocytoid. With the assistance of immunohistochemistry, demonstration of the number of cell types (mainly epithelial versus myoepithelial/basal) can further subclassify tumors within these morphologic categories. Additional tumor-specific immunomarkers are useful in some cases. Underlying tumor-specific genetic anomalies can be of value, however, immunohistochemical correlates are only available for some. When used judiciously, in the correct morphologic context, and with knowledge of their limitations, immunohistochemical stains can aid in differentiating tumors with similar morphology.

The Decline of Salivary Adenocarcinoma Not Otherwise Specified as a Tumor Entity: Reclassification Using Contemporary Immunohistochemical Profiling and Diagnostic Criteria

The classification of salivary gland carcinomas has become increasingly specific over the last decade with the definition of new tumor types, documentation of novel molecular and immunohistochemical findings, and development of more refined diagnostic criteria. In this setting, it is unclear how many salivary tumors still cannot be easily categorized-and whether such tumors represent undifferentiated malignancies or include additional definable entities. Relying largely on current classification schemes and contemporary immunohistochemical panels, we reassessed salivary tumors previously diagnosed as adenocarcinoma, not otherwise specified (ACA NOS) from 2 large academic medical centers. Fifty-seven ACA NOS (72%) could be reclassified as more specific entities including 31 salivary duct carcinomas (39%), 7 polymorphous adenocarcinomas (9%), 5 epithelial-myoepithelial carcinomas (6%), 4 myoepithelial carcinomas (5%), 4 secretory carcinomas (5%), 1 acinic cell carcinoma (1%), 1 basal cell adenocarcinoma (1%), 1 intraductal carcinoma (1%), and 1 clear cell carcinoma (1%) as well as 2 metastatic squamous cell carcinomas (3%). Of reclassified cases, 21 (37%) represented variant histologies within these categories. ACA NOS comprised 11% of salivary malignancies before reclassification, but only 4% after reclassification. The remaining 22 ACA NOS demonstrated heterogeneous features, with an association between histologic grade and clinical outcome. In effect, ACA NOS is becoming a bygone entity as modern classification schemes and ancillary techniques now permit more specific typing of a majority of these tumors, potentially facilitating more specific prognostication and treatment. Additional distinctive entities such as mucinous adenocarcinoma may still be definable within the ACA NOS category.

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.

A rare case of high-grade intraductal carcinoma of the upper lip: immunohistochemical and genetic analyses

Although intraductal carcinoma (IDC) of the salivary glands was previously called low-grade cribriform cystadenocarcinoma, it was newly categorized in the 4th version of the World Health Organization classification. We report a case of IDC of the upper lip and examined it immunohistochemically and genetically. The patient was a 48-year-old Japanese female, who noticed a tiny nodule on her left upper lip. Histologically, the tumor cells, which had eosinophilic cytoplasm, exhibited papillary and solid growth patterns, and regions of suspected microinvasion or intraductal spread were also seen at the periphery of the tumor. Small necrotic foci were noted. Immunohistochemically, the tumor cells were diffusely positive for the androgen receptor, CK19, CK5/6, EGFR, and SOX10, whereas they were focally positive for GCDFP-15, S-100 protein, and mammaglobin. The tumor nests were surrounded by alpha-smooth muscle actin-p63-/calponin-/CK14-positive myoepithelial cells. The Ki-67 labeling index was 51.2%. Genetic analysis showed no evidence of the TRIM27-RET or NCOA4-RET fusion gene. We finally diagnosed the tumor as a high-grade mixed intercalated duct/apocrine-type IDC of the upper lip. IDC of the minor salivary glands is exceedingly rare. We discuss diagnostic problems associated with minor salivary gland lesions, and the "basal-like" phenotype of this case.

SalvGlandDx - a comprehensive salivary gland neoplasm specific next generation sequencing panel to facilitate diagnosis and identify therapeutic targets

Diagnosis of salivary gland neoplasms is often challenging due to their high morphological diversity and overlaps. Several recurrent molecular alterations have been described recently, which can serve as powerful diagnostic tools and potential therapeutic targets (e.g. NTRK or RET fusions). However, current sequential molecular testing can be expensive and time consuming. In order to facilitate the diagnosis of salivary gland neoplasms, we designed an all-in-one RNA-based next generation sequencing panel suitable for the detection of mutations, fusions and gene expression levels (including NR4A3) of 27 genes involved in salivary gland neoplasms. Here we present the validation of the "SalvGlandDx" panel on FFPE histological specimen including fine needle aspiration (FNA) cell block material, against the standard methods currently used at our institution. In a second part we describe selected unique cases in which the SalvGlandDx panel allowed proper diagnosis and new insights into special molecular characteristics of selected salivary gland tumors. We characterize a unique salivary gland adenocarcinoma harboring a ZCCHC7-NTRK2 fusion, a highly uncommon spindle cell and pseudoangiomatoid adenoid-cystic carcinoma with MYBL1-NFIB fusion, and a purely oncocytic mucoepidermoid carcinoma, whereas diagnosis could be made by detection of a CRTC3-MAML2 rearrangement on the cell block specimen of the FNA. Further, a rare case of a SS18-ZBTB7A rearranged low-grade adenocarcinoma previously described as potential spectrum of microsecretory adenocarcinoma, is reported. In addition, features of six cases within the spectrum of polymorphous adenocarcinoma / cribriform adenocarcinoma of salivary gland including PRKD1 p.E710D mutations and novel fusions involving PRKAR2A-PRKD1, SNX9-PRKD1 and ATL2-PRKD3, are described.

The Myoepithelial Cells of Salivary Intercalated Duct-type Intraductal Carcinoma Are Neoplastic: A Study Using Combined Whole-slide Imaging, Immunofluorescence, and RET Fluorescence In Situ Hybridization

Intraductal carcinoma (IDC) is a salivary gland tumor currently believed to be analogous to breast ductal carcinoma in situ, consisting of a complex neoplastic epithelial proliferation surrounded by a continuous layer of myoepithelial cells presumed to be native and non-neoplastic. Recent molecular insights have shown that there are at least 3 different types of IDC: (1) intercalated duct-like, with frequent NCOA4-RET fusions; (2) apocrine, with multiple mutations similar to salivary duct carcinoma; and (3) mixed intercalated duct-like and apocrine with frequent RET fusions, especially TRIM27-RET. Recent observations (eg, IDC occurring in lymph nodes) have challenged the notion that the myoepithelial cells of IDC are non-neoplastic. Five IDCs with known RET fusions by RNA sequencing were retrieved from the authors' archives, including 4 intercalated duct-like IDCs with NCOA4-RET, and 1 mixed intercalated duct-like/apocrine IDC with TRIM27-RET. A panel of immunohistochemistry antibodies (S100 protein, p63 or p40, mammaglobin, smooth muscle actin, calponin, androgen receptor) was tested. To precisely localize RET split-positive cells, each case was subjected to sequential retrieval of whole-slide imaging data of hematoxylin and eosin (HE) staining, immunofluorescence staining for calponin, and fluorescence in situ hybridization (FISH) for RET. Because NCOA4-RET is an inversion difficult to visualize on conventional RET FISH, a novel 3-color FISH technique was utilized to demonstrate it clearly. In all 5 cases, the proliferative ducts were completely surrounded by a layer of myoepithelial cells that were positive for p63 or p40, smooth muscle actin, and calponin. Using combined HE, calponin immunofluorescence, and RET FISH imaging, the positive signals were unmistakably identified in both calponin-negative ductal cells and peripheral, calponin-positive myoepithelial cells in all 5 cases. Utilizing combined HE, calponin immunofluorescence, and RET FISH imaging, we demonstrated that IDCs with RET fusions harbored this alteration in both the ductal and myoepithelial cells. This is compelling evidence that the myoepithelial cells of IDC are not mere bystanders, but are rather a component of the neoplasm itself, similar to other biphasic salivary gland neoplasms like pleomorphic adenoma and epithelial-myoepithelial carcinoma. This finding raises questions about the appropriate terminology, classification, and staging of IDC.

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.