Combined DOG1 and Mammaglobin Immunohistochemistry Is Comparable to ETV6-breakapart Analysis for Differentiating Between Papillary Cystic Variants of Acinic Cell Carcinoma and Mammary Analogue Secretory Carcinoma

Molecular Pathology of Thyroid Tumors: Old Problems and New Concepts

The molecular signatures of many thyroid tumors have been uncovered. These discoveries have translated into clinical practice and are changing diagnostic and tumor classification paradigms. Here, the findings of recent studies are presented with special emphasis on how molecular insights are impacting the understating of RAS mutant thyroid nodules, Hürthel cell neoplasms, and unusual thyroid tumors, such as hyalinizing trabecular tumor, secretory carcinoma of the thyroid, and sclerosing mucoepidermoid carcinoma with eosinophilia. In addition, the utility of detecting actionable molecular alterations by immunohistochemistry in advanced and aggressive thyroid cancer is also discussed.

Clinicopathological analysis of 18 cases of secretory carcinoma of the salivary glands

Background/purpose

Secretory carcinoma (SC) is a rare salivary gland tumor that featured by ETV6::NTRK3 gene fusion, and was included in the WHO Classification of Head and Neck Tumors since 2017. Nevertheless, the description of SCs by WHO is still vague. This study examined 18 SC cases by using both histomorphology and molecular pathology for diagnostic determination, especially immunohistochemical features of SCs.

Materials and methods

Based on WHO characteristics, 18 patients with SC admitted between 2001 and 2022 were included in this study. Main histomorphological patterns, FISH analyses of the ETV6::NTRK3 gene fusion, and immunohistochemical analyses of S100, mammaglobin, DOG1, ADFP, CA6 and Ki-67 were performed.

Results

Among the 18 SC patients, the median age of onset was 39.22 years. Grossly, the average tumor size in 2.96 cm with various texture from soft to tough. The majority patients were positive for S100, mammaglobin, and negative for DOG1, except for one patient negative for S100 (Case 18). All patients were positive for ADFP, and the majority patients were negative for CA6, except for Case 9. Two cases were found recurrence, and the tumor were found both in parotid gland with local invasion.

Conclusion

Combined with the results of previous studies, we proposed that the combination of all five markers, S100, mammaglobin, DOG1, ADFP and CA6, could contribute more to differential diagnosis of SCs with other salivary carcinomas, especially with AciCC. The prognosis of SCs is optimistic in most cases, but larger patient cohort and long-term follow-up are still needed.

DOG1 as an Immunohistochemical Marker of Acinic Cell Carcinoma: A Systematic Review and Meta-Analysis

DOG1 is a transmembrane protein originally discovered on gastrointestinal stromal tumors and works as a calcium-activated chloride channel protein. There are a limited number of articles on the potential utility of this antibody in the diagnosis of salivary gland tumors in routine practice. In this study, we aimed to investigate the role of DOG1 as an immunohistochemical marker in patients with salivary acinic cell carcinoma (ACC) through meta-analysis. A literature search was performed of the PubMed, Scopus, and Web of Science databases for English-language studies published from January 2010 to September 2021. The literature search revealed 148 articles, of which 20 were included in the study. The overall rate of DOG1 expression in salivary acinic cell carcinoma was 55% (95% CI = 0.43–0.58). Although ACC is a challenging diagnosis, paying careful attention to the cytomorphological features in conjunction with DOG1 immunostaining can help to reach an accurate diagnosis.

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.

A systematic review of secretory carcinoma of the salivary gland: where are we?

OBJECTIVE

The aim of this systematic review was to describe the epidemiology, diagnostic criteria, differential diagnosis, treatment, prognostic factors, and treatment outcomes of secretory carcinoma.

STUDY DESIGN

A comprehensive search of Lilacs, PubMed, Science Direct, and Web of Science databases was conducted to identify all case reports, letter to the editor, and histopathologic reclassifications regarding salivary gland secretory carcinoma published in English, Spanish, French, and Portuguese.

RESULTS

The final analysis included 119 studies, which totaled 642 secretory carcinoma diagnoses, with 239 case reports and 403 diagnostic reclassifications, mostly in the United States. The age range was 5 to 87 years, and cases were predominantly in males (58.7%) and mostly affecting the parotid glands (73.7%). The disease usually presents as a slow-growing, painless mass. The main differential diagnosis is acinic cell carcinoma, and the tumor is usually treated with surgery. The prognosis is considered favorable, although there have been reports of local recurrences, distant metastases, and deaths.

CONCLUSIONS

It is important that clinicians become aware of this salivary gland neoplasm and report clinical data, clinical course, management and long-term follow-up. There is an urgent need to conduct more clinical trials, especially on tropomyosin receptor kinase (TRK) inhibitors and other potential target therapy modalities.

Molecular Pathology of Thyroid Tumors: Old Problems and New Concepts

The molecular signatures of many thyroid tumors have been uncovered. These discoveries have translated into clinical practice and are changing diagnostic and tumor classification paradigms. Here, the findings of recent studies are presented with special emphasis on how molecular insights are impacting the understating of RAS mutant thyroid nodules, Hürthel cell neoplasms, and unusual thyroid tumors, such as hyalinizing trabecular tumor, secretory carcinoma of the thyroid, and sclerosing mucoepidermoid carcinoma with eosinophilia. In addition, the utility of detecting actionable molecular alterations by immunohistochemistry in advanced and aggressive thyroid cancer is also discussed.

Differential diagnosis and treatment of salivary secretory carcinoma and acinic cell carcinoma

Secretory carcinoma (SC) and acinic cell carcinoma (AciCC) are two rare tumors originating in the salivary gland of the head and neck. Before the World Health Organization (WHO) classified SC as a new entity in 2017, the majority of SC cases were incorrectly diagnosed as AciCC. Indeed, they are similar in biological behaviors, clinical manifestations and histomorphological features. Especially, SC and zymogen granule-poor AciCC are difficult to differentiate, which brings a tough challenge in clinical diagnosis. This article provides an updated understanding of the differential diagnosis in SC and AciCC from two main perspectives: histopathology and molecular genetics. The targeted therapies for both tumors are also mentioned. It aims to give some hints in clinical diagnosis and treatment, in hopes that patients with adequate diagnosis could obtain the opportunityformore effective treatment.

Unusual Presentations of Primary and Metastatic Adenoid Cystic Carcinoma Involving the Skin

Adenoid cystic carcinoma (ACC) is most commonly seen in the salivary glands but may occur at other sites. Primary or metastatic involvement of the skin is unusual. We report 2 cases of ACC with unusual presentation. In the first case, a 55-year-old woman presented with a cutaneous lesion on the right shin, and final pathology showed ACC. An extracutaneous origin was excluded by clinical and imaging studies. In the second case, a 49-year-old woman presented with a nodule on the breast, and biopsy confirmed high-grade ACC (>30% solid areas). She underwent lumpectomy and subsequent mastectomy after recurrence. Sixteen months after the initial diagnosis of ACC of the breast, distant metastases at multiple sites, including the skin, were identified. This report will increase awareness of these rare presentations of cutaneous ACC and allow correct diagnosis and appropriate management of such cases.

Characterization of novel genetic alterations in salivary gland secretory carcinoma

Secretory carcinoma is a salivary gland tumor with a characteristic chromosomal translocation that results in an ETV6-NTRK3 fusion gene. Secretory carcinoma shows relatively frequent rates of lymph-node metastasis and tumor recurrence and has a characteristic histology. Except for the ETV6 translocation, genomic alterations in secretory carcinoma have not been reported. In the present study, we characterized the novel recurrent genetic mutations of secretory carcinoma. On the basis of histology, immunohistochemistry, and ETV6 gene break-apart fluorescence in situ hybridization assays, 22 tumors were classified as secretory carcinomas (19 ETV6 translocation-positive and 3 ETV6 translocation-negative secretory carcinomas) and their clinicopathologic characteristics were reviewed. Targeted deep sequencing analyses were performed on 20 secretory carcinomas (17 ETV6 translocation-positive and 3 ETV6 translocation-negative secretory carcinomas) to investigate their genetic alterations. The A16V (C→T) mutation in PRSS1, which encodes a cationic trypsinogen and has a mutation associated with hereditary pancreatitis and pancreatic adenocarcinoma, was observed in 40% (8/20) (7/17 of ETV6 translocation-positive and 1/3 of ETV6 translocation-negative secretory carcinomas). Pathogenic variants of MLH1, MUTYH, and STK11 were also identified. Variants of uncertain significance included mutations in KMT5A. These novel characteristic genetic alterations may advance current understandings of secretory carcinoma tumorigenesis and progression, leading to improved diagnoses and treatment strategies.

A Challenging Case of Mammary Analogue Secretory Carcinoma: Case Study with Ultrastructural and Cytogenetic Correlation

Mammary analogue secretory carcinoma (MASC) is a rare salivary gland tumor analogous to secretory carcinoma of the breast. The diagnosis of MASC can be challenging due to substantial morphologic and immunohistochemical similarities with other salivary gland tumors. The differential diagnosis of MASC is broad and includes intraductal carcinoma, acinic cell carcinoma, and adenocarcinoma, not otherwise specified. Although molecular testing for ETV6 gene rearrangement is characteristic of MASC and has not been shown in any other salivary gland tumor, a particular challenge arises when such testing is unavailable, or when molecular testing for ETV6 gene rearrangement is negative in a suspected case of MASC. Our study presents the diagnostic workup of a challenging case of MASC with immunohistochemistry, electron microscopy, and cytogenetic studies performed to resolve the diagnosis.

The key radiologic and cytomorphologic features of oncocytic and oncocytoid lesions of the salivary gland

Oncocytic and oncocytoid lesions represent a distinct subset of salivary gland lesions. True oncocytic lesions of the salivary gland are entirely composed of oncocytes. These are characterized by the presence of abundant eosinophilic granules due to the presence of abundant cytoplasmic mitochondria. Oncocytic lesions of the salivary gland include oncocytosis, oncocytoma, and oncocytic carcinoma. In addition to the true oncocytic lesion, there exists another group of salivary gland lesions, which demonstrate cells with abundant and occasionally granular cytoplasm. These are often termed as "oncocytoid" lesions. The recently proposed Milan System for reporting salivary gland cytology clearly states that fine-needle aspiration specimens representing oncocytic/oncocytoid lesions of salivary gland cannot effectively distinguish between a nonneoplastic lesion, benign and malignant neoplasms. Therefore, most lesions lacking classic cytomorphologic features will be classified under the umbrella diagnostic term of "Salivary Gland Neoplasm of Uncertain Malignant Potential" (SUMP). In this review, we discuss and illustrate key clinicopathologic and radiologic features that can help the practicing cytopathologist narrow down the differential and provide the best management based diagnosis.

Secretory Carcinoma of Minor Salivary Gland in Buccal Mucosa: A Case Report and Review of the Literature

Secretory carcinoma (SC) of the salivary gland was recently added to the fourth edition of the World Health Organization classification of head and neck tumors. Some salivary tumors, including acinic cell carcinoma, have been reclassified as SC. Most of these tumors are located on the parotid gland with very few cases reported in the minor salivary glands of the buccal mucosa. Herein, we present a case of SC of buccal mucosa, which appeared clinically as a benign lesion in a 54-year-old Japanese female patient. Histopathologically, the tumor cells presented with an eosinophilic cytoplasm with microcytic structure along with eosinophilic secretory material and hemosiderin deposit. Immunohistochemical staining revealed strongly positive staining for S100, vimentin, and mammaglobin and negative staining for DOG-1. The tumor was finally diagnosed as secretory carcinoma of the buccal mucosa. We present a review of the medical literature of SC arising from minor salivary glands. We found only 15 cases of SC of buccal mucosa out of 63 cases of SC in the minor salivary glands. They showed good prognoses and only one case of SC in the buccal mucosa exhibited local recurrence and lymph node metastases.

Primary Pulmonary Acinic Cell Carcinoma: A Clinicopathological Study of 6 Cases and Literature Review

Primary pulmonary acinic cell carcinoma (ACC) is rare. The clinicopathological features are not identical to that of classic ACC that leads to misdiagnosis. In this article, we summarized the clinicopathological features of 25 such cases, including 6 cases in this series and additional 19 cases in the literature. Pulmonary ACCs showed an overwhelming solid growth pattern. The neoplastic cells had eosinophilic granular and clear cytoplasm in most cases and displayed basophilic cytoplasm in only 4 cases. Intratumoral fibrous septa, mitotic figure, necrosis, and psammoma bodies were observed in some cases. Prominent nuclear atypia and perineural invasion might suggest high-grade transformation, metastasis, and recurrence. The tumor cells were strongly positive for CK8/18 and negative for TTF-1, p63, S-100, mammaglobin, MUC5b, MUC5ac, and DOG1. CK7 was exclusively positive for neoplastic cells with ductal differentiation. Of the 25 included cases, 10 cases were initially misdiagnosed. The tumor was prone to involve the right bronchus. The patient outcome was favorable. The accurate diagnosis of primary pulmonary ACC relies on comprehensive evaluation of histological and immunohistochemical features and realization of the difference from classic ACC.

Secretory Carcinoma of the Parotid: Making the Correct Diagnosis of a Rare Salivary Gland Carcinoma When Molecular Biology Testing Is Not Available

Secretory carcinoma (SC) is a recently described entity occurring in the salivary glands. Before its description, SC was frequently classified as acinic cell carcinoma (ACC) or adenocarcinoma, not otherwise specified. Its particular histopathological and immunohistochemical characteristics are reminiscent of breast secretory carcinoma. Moreover, it displays a characteristic t(12;15) (p13;q25) translocation that results in the ETV6-NTRK3 gene fusion. This translocation has not been reported in any other salivary gland carcinoma. Identification of the t(12;15) (p13;q25) translocation is the gold standard for diagnosis, although some cases that do not present this specific translocation have already been reported. In such cases, diagnosis is challenging. In addition, some diagnostic pathology laboratories lack the resources to perform the molecular analysis to diagnose SC. In this scenario, morphology and immunohistochemistry are fundamental. Therefore, we report a case emphasizing the typical morphology of SC and its immunochemical profile to establish a final diagnosis without molecular biology tests. This case aims to demonstrate the importance of recognizing the typical presentation of a rare tumor so that clinicians will be informed or reminded of it and consider this entity among the differential diagnoses, when necessary. Moreover, in low-resource settings where molecular analysis is not available, being familiar enough with the histology of this tumor and using the immunoprofile as a key tool for differential diagnosis would be of great importance in establishing the correct diagnosis. The differential diagnosis includes, above all, acinic cell carcinoma and other salivary neoplasms such as intraductal carcinoma, low-grade mucoepidermoid carcinoma, and adenocarcinoma, not otherwise specified, which is actually a rule-out diagnosis.

Salivary Secretory Carcinoma With a Novel ETV6-MET Fusion: Expanding the Molecular Spectrum of a Recently Described Entity

Secretory carcinoma of the salivary glands, also known as mammary analogue secretory carcinoma, is a recently described tumor characterized by generally indolent clinical behavior and recurrent ETV6-NTRK3 fusions. However, a small subset of recent cases with high-grade histology, aggressive behavior, or alternate molecular findings are expanding the spectrum of this entity. In this case, a 59-year-old female presented with an infiltrative submandibular gland tumor that was originally classified as a high-grade acinic cell carcinoma, papillary-cystic variant. She developed persistent local disease and, 11 years after initial presentation, was found to have widespread metastases. Rereview of her primary tumor highlighted microcystic, papillary, and solid architecture, eosinophilic cytoplasm, vesicular nuclei with prominent nucleoli, abundant mitotic figures, and necrosis. Immunostains showed the tumor cells to be positive for S100 and mammaglobin and negative for DOG-1, and fluorescence in situ hybridization highlighted an ETV6 rearrangement, supporting a diagnosis of high-grade secretory carcinoma. Finally, next-generation sequencing demonstrated a novel ETV6-MET fusion. To our knowledge, this is the first ETV6-MET fusion reported in secretory carcinoma. This finding further expands the definition of secretory carcinoma while carrying implications for selecting appropriate targeted therapy.

Synchronous Parotid (Mammary Analog) Secretory Carcinoma and Acinic Cell Carcinoma: Report of a Case

Mammary analogue secretory carcinoma (MASC) is a recently described low-grade salivary gland malignancy with histologic, immunohistochemical and molecular similarities to secretory carcinoma of the breast, including a specific t(12;15)(p13;q25) resulting in an ETV6-NTRK3 gene fusion. Ultrasound and magnetic resonance imaging frequently document a macrocystic structure. The main differential diagnosis of secretory carcinoma is with low grade acinic cell carcinoma (AciCC). The two can be differentiated with immunohistochemical stains for S100, mammaglobin, carbonic anhydrase VI and DOG-1; the identification of the specific translocation can help to characterize non-typical cases. We report a unique case of synchronous MASC and AciCC presenting in a parotid gland and discuss the implications of the correct identification of the two tumors.

Characterisation of DOG-1 Expression in Salivary Gland Tumours and Comparison with Myoepithelial Markers

DOG1 is an established diagnostic marker for gastrointestinal stromal tumours (GIST), but has been reported in salivary gland tumours (SGT) as an acinar and intercalated duct marker. However, its specificity and distribution is not well established. The aim of this study was to evaluate the diagnostic utility of DOG-1 expression in SGT in addition to comparing it with myoepithelial markers. Normal salivary tissue and SGT (n = 184) were examined for expression of DOG1 and a range of myoepithelial markers. SGT included: acinic cell carcinoma (ACC, n = 15), secretory carcinoma (SC, n = 9), pleomorphic adenoma (PA, n = 49), carcinoma ex-PA (Ca ex-PA, n = 11), adenoid cystic carcinoma (AdCC, n = 20), polymorphous adenocarcinoma (PAC, n = 6), myoepithelioma (n = 6), myoepithelial carcinoma (MC, n = 2), basal cell adenoma (BCA, n = 14), canalicular adenoma (CA, n = 19), mucoepidermoid carcinoma (MEC, n = 11), oncocytoma (n = 2), adenocarcinoma NOS (AdNOS, n = 4), basal cell adenocarcinoma (BCAC, n = 2), salivary duct carcinoma (SDC, n = 3) and papillary cystadenocarcinoma (PCAC, n = 1). Normal acini and ACC (14/15) showed strong luminal DOG1 staining; SC were largely negative with only focal expression in 3/9 cases. Luminal staining was seen in PA (14/49), PAC (4/6), Ca ex-PA (4/11) and AdCC (6/20). 8/11 MEC showed luminal and/or mucous cell staining. No staining was seen in myoepithelioma, MC, CA, adNOS and BCAC. BCA showed strong staining of myoepithelial cells in some cases (5/14). Variable myoepithelial DOG1 staining was seen in PA, Ca ex PA, BCA, SDC and PCAC which was not as consistent as myoepithelial markers such as calponin, p63 and αSMA. Absence of DOG1 can differentiate ACC from SC, but staining is variable in PA, PLGA and Ca ex-PA. Myoepithelial staining in some tumours but not in normal gland suggests a wider distribution in SGT than originally envisaged.

Primary mammary analogue secretory carcinoma of the lung: a case report

Mammary analogue secretory carcinoma (MASC) is a recently discovered salivary gland tumor described mostly in the major salivary glands and occasionally in the skin. We report a primary endobronchial tumor with histology, immunophenotype, and ETV6 rearrangement characteristic of MASC in a 62-year-old woman. The diagnosis was initially made on a transbronchial biopsy with fluorescence in situ hybridization confirmation of ETV6 rearrangement. The patient underwent lobectomy demonstrating a large endobronchial mass. To our knowledge, this is the first report of MASC arising as a primary pulmonary tumor. This tumor was unusual in that it is the largest (8.5 cm) MASC ever reported, showed an increased mitotic count (6/10 high-power fields) without high-grade cytology, and presented with advanced-stage disease that included visceral pleural invasion and lymph node metastasis.

Diagnostic Approach to Fine Needle Aspirations of Cystic Lesions of the Salivary Gland

Fine needle aspiration (FNA) has diagnostic and therapeutic value in the management of salivary gland cysts. Rendering an accurate diagnosis from an aspirated salivary gland cyst is challenging because of the broad differential diagnosis, possibility of sampling error, frequent hypocellularity of specimens, morphologic heterogeneity, and overlapping cytomorphology of many cystic entities. To date, there have been no comprehensive review articles providing a practical diagnostic approach to FNA of cystic lesions of salivary glands. This article reviews the cytopathology of salivary gland cysts employing 2017 World Health Organization terminology, addresses the accuracy of FNA, and presents The Milan System approach for reporting in cystic salivary gland cases. The utility of separating FNA specimens from salivary gland cysts, based upon the presence of mucin and admixed lymphocytes in cyst fluid is demonstrated. A reliable approach to interpreting FNA specimens from patients with cystic salivary gland lesions is essential to accurately determine which of these patients may require subsequent surgery.

Diagnostic Approaches for Salivary Gland Tumors with Secretory and Microcystic Features

Secretory carcinoma (SC) of the salivary gland is a new entity that shares the unique morphologic features and cytogenetic characteristics of the ETV6-NTRK3 fusion gene with its breast counterpart. Before identification of SC of the salivary gland, it was most frequently diagnosed as acinic cell carcinoma (AciCC). We retrospectively reviewed our own database of salivary gland tumors harboring microcystic and papillary architecture and/or secretory features that were originally diagnosed as AciCC. We selected nine cases of AciCC showing diffuse S-100 expression on immunohistochemistry (IHC). A recently diagnosed case of SC was included in the study as a reference sample. We performed IHC of S-100 and mammaglobin and ETV6 gene fluorescence in situ hybridization (FISH) in all cases. Seven cases were positive for both S-100 and mammaglobin, while five of the seven (71.4%) demonstrated ETV6 gene translocation by FISH. In the cases which did not co-express either S-100 or mammaglobin on IHC, ETV6 gene rearrangement was not shown on FISH. In conclusion, if a salivary gland tumor has morphologic features of SC with co-expression of S-100 and mammaglobin, ETV6 FISH can be performed to confirm the diagnosis of SC of the salivary gland.

Mammary analogue secretory carcinoma of salivary glands: diagnostic pitfall with distinct immunohistochemical profile and molecular features

Mammary analogue secretory carcinoma (MASC) is a newly defined entity among salivary gland malignancies which has just been established in the 4^th edition of the WHO classification of head and neck tumors. MASC (synonym: secretory carcinoma) are characterized by a specific rearangement of the ETV6 gene locus. Here, we present a series of 3 MASC cases including clinical data with follow-up for up to 26 months. All tumours immunhistochemically displayed strong positivity for cytokeratin 7, and mammaglobin, focal positivity for S100, cytokeratin 5/6 and muc-4. In contrast, immunhistochemical stainings against cytokeratin 14, hormon receptors, Her2/neu, androgen receptor and prostate-specific antigen were consistently negative. FISH analysis showed translocation of the ETV6 gene locus in the majority of tumour cell nuclei. During clinical follow-up, no local relapse or metastasis was detected. As these carcinomas are clinically and radiologically indistinguishable from other salivary gland tumours and as therapeutic approaches and prognosis might differ, we need to be able to diagnose MASC correctly.

Genomic profiling of breast secretory carcinomas reveals distinct genetics from other breast cancers and similarity to mammary analog secretory carcinomas

Secretory carcinomas of the breast are rare tumors with distinct histologic features, recurrent t(12;15)(p13;q25) translocation resulting in ETV6-NTRK3 gene fusion and indolent clinical behavior. Mammary analog secretory carcinomas arising in other sites are histopathologically similar to the breast tumors and also harbor ETV6-NTRK3 fusions. Breast secretory carcinomas are often triple (estrogen and progesterone receptor, HER2) negative with a basal-like immunophenotype. However, genomic studies are lacking, and whether these tumors share genetic features with other basal and/or triple negative breast cancers is unknown. Aside from shared ETV6-NTRK3 fusions, the genetic relatedness of secretory carcinomas arising in different sites is also uncertain. We immunoprofiled and sequenced 510 cancer-related genes in nine breast secretory carcinomas and six salivary gland mammary analog secretory carcinomas. Immunoprofiles of breast and salivary gland secretory carcinomas were similar. All the tumors showed strong diffuse MUC4 expression (n=15), and SOX10 was positive in all nine breast and in five out of six salivary gland tumors. All breast secretory carcinomas were triple negative or weakly ER-positive, and all tumors at both the sites expressed CK5/6 and/or EGFR, consistent with a basal-like phenotype. Sequencing revealed classic ETV6-NTRK3 fusion genes in all cases, including in carcinoma in situ of one breast tumor. Translocations were reciprocal and balanced in six out of nine breast and three out of six salivary gland tumors and were complex in three others. In contrast to most breast basal carcinomas, the mutational burden of secretory carcinomas was very low, and no additional pathogenic aberrations were identified in genes typically mutated in breast cancer. Five (56%) breast and two (33%) salivary gland tumors had simple genomes without copy number changes; the remainder had very few changes, averaging 1.3 per tumor. The ETV6-NTRK3 derivative chromosome was duplicated in one breast and one salivary gland tumor, and was the only copy number change in the latter. The findings highlight breast secretory carcinoma as a subtype more closely related to mammary analog secretory carcinoma than to basal/triple negative breast cancers of no special type. Lack of pathogenic mutations in common cancer-related genes suggests that ETV6-NTRK3 alone may suffice to drive these tumors and likely helps explain their indolent behavior.

Secretory carcinoma - impact of translocation and gene fusions on salivary gland tumor

Secretory carcinoma (SC), previously described as mammary analogue secretory carcinoma (MASC), is a recently described salivary gland tumor which morphologically resembles mammary secretory carcinoma. The first description of SC/MASC, reported by Skálová et al. in 2010, was as a rare salivary carcinoma imitating secretory carcinoma of the breast. SC/MASC is a unique salivary gland tumor with morphological overlap with acinic cell carcinoma (AciCC), mucoepidermoid carcinoma (MEC), and adenocarcinoma not otherwise specified (ADC-NOS). SC/MASC shares similar clinicopathological features with AciCC. As a critical difference between SC/MASC and AciCC, SC/MASC characteristically has the chromosomal translocation t(12;15)(p13;q25) which leads to a fusion gene between the ETV6 gene on chromosome 12 and the NTRK3 gene on chromosome 15. This genetic background is an important differential diagnostic finding for excluding other salivary gland tumors and may be a critical factor determining the prognosis for patients with SC/MASC. Research in recent years has provided a large body of new data on SC/MASC and suggests the possibility that the ETV6-NTRK3 translocation could be a therapeutic target. Here, we review the morphological and clinicopathological features of SC/MASC and discuss new directions for therapy.