Re-evaluating a historic cohort of sinonasal and skull base mucoepidermoid carcinoma: an institutional experience.

AIMS: Primary mucoepidermoid carcinomas (MECs) of the sinonasal tract and nasopharynx are rare entities that represent a diagnostic challenge, especially in biopsy samples. Herein, we present a case series of MECs of the sinonasal and skull base and its mimics to evaluate the clinicopathological and molecular characteristics in order to avoid misdiagnosis. METHODS: We reviewed the pathology records of patients diagnosed from 2014 to 2022. Thirty MECs were consecutively diagnosed during that period. RESULTS: Based on morphological and fluorescence in situ hybridization (FISH) analyses, 30 tumors originally diagnosed as MECs were separated into MAML2 fusion-positive (7 cases) and MAML2 fusion-negative groups (23 cases), in which 14 tumors were positive for the EWSR1::ATF1 fusion; these tumors were reclassified to have hyalinizing clear cell carcinoma (HCCC). The remaining nine MAML2 FISH negative cases were reconfirmed as squamous cell carcinoma (SCC, 3 cases) which showed keratinization and high Ki-67 expression; DEK::AFF2 carcinomas (2 cases), in which DEK gene rearrangement was detected by FISH; and MECs as previously described (4 cases) with typical morphological features. Including 7 MAML2 rearrangements tumors, 11 MEC cases had a male-to-female ratio of 4.5:1, and 6 tumors arose from the nasopharyngeal region, while 5 tumors arose from the sinonasal region. The prognosis of this series of salivary gland-type MECs was favorable. CONCLUSIONS: Our study confirmed that HCCC runs the risk of being misdiagnosed as MEC in the sinonasal tract and nasopharynx, particularly with biopsy specimens. Careful histological evaluation with supporting molecular testing can facilitate pathological diagnoses.

A high-grade breast mucoepidermoid carcinoma without MAML2 rearrangement: A case report and literature review.

INTRODUCTION: Mucoepidermoid carcinoma (MEC) of the breast is an extremely rare primary breast tumor. Between 1979 and June 2022, only 50 cases were reported. The pathological morphology and biological behavior of breast MEC remain poorly understood. PATIENT CONCERNS: A 47-year-old female was presented with a 10-day-old left breast mass detected by physical examination. DIAGNOSES: Ultrasonography could not distinguish whether the breast tumor was benign or malignant. After a biopsy of a breast tumor excision specimen, combined with immunohistochemical results, the patient was diagnosed with high-grade mucoepidermoid breast carcinoma. INTERVENTIONS: The patient underwent a modified radical mastectomy for her left breast. OUTCOMES: The patient was still free from local recurrence or metastases at 1-year follow-up. CONCLUSION: A high-grade MEC case without MAML2 rearrangement shows good recovery without complications. The diagnosis was confirmed by histomorphology and immunohistochemical markers. It is sometimes necessary to distinguish it from adenosquamous, adenoid cystic, or mucinous carcinoma. The primary treatment is surgical resection, and the prognosis is closely related to the pathological grade.

Genomics and tumor microenvironment of breast mucoepidermoid carcinoma based on whole-exome and RNA sequencing.

Mammary mucoepidermoid carcinoma (MEC) is a rare entity. The molecular characteristics of breast MEC have not been fully investigated due to its rarity. We performed a retrospective study among 1000 patients with breast carcinomas and identified four cases of breast MEC. Clinical and demographic data were collected. Immunohistochemistry panels which were used to diagnose salivary gland MEC and breast carcinomas were also performed. MAML2 rearrangements were detected by FISH and fusion partners were identified by RNA sequencing. Whole-exome sequencing (WES) was used to reveal the genomes of these four breast MEC. Then, the biological functions and features of breast MEC were further compared with those of invasive breast carcinomas and salivary gland MEC.According to Ellis and Auclair's methods, these four breast MEC could be classified as low-grade breast MEC. All the patients were alive, and disease-free survival (PFS) ranged from 20 months to 67 months. Among these four breast MEC, two cases were triple-negative, and the other two cases were found to be ER positive, with one also showing HER2 equivocal by immunohistochemical staining, but no amplification in FISH. FISH analysis confirmed the presence of the MAML2 translocation in three of four tumors, and CRTC1-MAML2 fusion was confirmed in two of them by RNA-sequencing. The average coverage size of WES for the tumor mutation burden estimation was 32 Mb. MUC4, RP1L1 and QRICH2 mutations were identified in at least three tumors, and these mutation also existed in breast invasive carcinoma databases (TCGA, Cell 2015; TCGA, Nature 2012). The results showed that there were many genes in breast MEC overlapping with the breast invasive carcinoma databases mentioned above, range from 5 to 63 genes (median:21 genes). Next, we assessed immune cell infiltration levels in these tumors. In all these tumors, M2 macrophages and plasma cell were in the high infiltration group. Our breast MEC showed different results from the salivary gland MEC, whose plasma cells were in the low infiltration group. Overall, we first analyzed the genomics and tumor microenvironment of breast mucoepidermoid carcinoma and proposed our hypothesis that although MECs arising in the breast resemble their salivary gland counterparts phenotypically, our findings indicate that breast MECs probably resemble invasive breast carcinomas at the genetic level and immune cell infiltration levels. More cases and in deep research need to be done to further understand this rare carcinoma.

Heterogeneity in PD-L1 expression in MAML2-rearranged mucoepidermoid carcinoma.

OBJECTIVE: Mucoepidermoid carcinoma (MEC) is a malignant tumor with diverse morphologies, some of which have poor prognostic indicators and others that challenge the grading system. This study investigated the expression of PD-L1 in different grades and phenotypes of MEC. METHODS: The present study was carried out on twenty-four archival formalin-fixed, paraffin-embedded blocks of salivary MEC. Fluorescence in situ hybridization was used to detect MAML2 rearrangement in MEC cases to be included. The studied cases were then subcategorized based on their grading and phenotype and immunohistochemically stained for PD-L1. RESULTS: PD-L1 expression in MEC varied, with some variants showing moderate to strong immunoexpression, while others did not express it at all. In the Warthin-like MEC, some tumors show high expression of PD-L1, while in the same pattern, a few cases showed low or no expression. Intraosseous MEC exhibited moderate PD-L1 expression. Sclerosing MEC featured lower PD-L1 expression, from weak to moderate. Oncocytic MEC displayed relatively low PD-L1 expression levels (weak to moderate). CONCLUSION: The histomorphologic features of MEC may predict clinicopathologic behavior, and subtyping MEC may pose a significant therapeutic value, particularly for intraosseous MECs and clear-cell MECs. PD-L1 expression is a good predictor of survival outcomes in MECs.

Current diagnosis and treatment of salivary gland-type tumors of the lung.

Salivary gland-type tumors of the lung are thought to originate from the submucosal exocrine glands of the large airways. Due to their rare occurrence, reports of their study are limited to small-scale or case reports. Therefore, daily clinical practices often require a search for previous reports. In the last 20 years, several genetic rearrangements have been identified, such as MYB::NF1B rearrangements in adenoid cystic carcinoma, CRTC1::MAML2 rearrangements in mucoepidermoid carcinoma, EWSR1::ATF1 rearrangements in hyalinizing clear cell carcinoma and rearrangements of the EWSR1 locus or FUS (TLS) locus in myoepithelioma and myoepithelial carcinoma. These molecular alterations have been useful in diagnosing these tumors, although they have not yet been linked to molecularly targeted therapies. The morphologic, immunophenotypic, and molecular characteristics of these tumors are similar to those of their counterparts of extrapulmonary origin, so clinical and radiologic differential diagnosis is required to distinguish between primary and metastatic disease of other primary sites. However, these molecular alterations can be useful in differentiating them from other primary lung cancer histologic types. The management of these tumors requires broad knowledge of the latest diagnostics, surgery, radiotherapy, bronchoscopic interventions, chemotherapy, immunotherapy as well as therapeutic agents in development, including molecularly targeted agents. This review provides a comprehensive overview of the current diagnosis and treatment of pulmonary salivary gland tumors, with a focus on adenoid cystic carcinoma and mucoepidermoid carcinoma, which are the two most common subtypes.

High-grade HER2-positive mucoepidermoid carcinoma of the breast: a case report and review of the literature.

BACKGROUND: Mucoepidermoid carcinoma of the breast is a rare special type of salivary gland-like tumor of the breast, usually displaying triple-negative phenotype. To date, only 64 cases have been reported in the English literature. Herein, we report the first case of mucoepidermoid carcinoma of the breast with human epidermal growth factor receptor 2 gene amplification. CASE PRESENTATION: A 58-year-old Caucasian woman treated with breast-conserving surgery, radiotherapy, and chemotherapy for an invasive breast carcinoma of no special type, relapsed 20 years later in the ipsilateral left breast. Histological examination of the core needle biopsy of the relapse deferred to the surgical specimen for the definitive diagnosis, because of the broad differential diagnosis. On the resected specimen we observed the presence of a poorly differentiated carcinoma with mucoepidermoid carcinoma of the breast typical features consisting of epidermoid, intermediate and mucinous cells lacking true keratinization, in keeping with the latest World Health Organization diagnostic criteria. The mucoepidermoid carcinoma of the breast was weakly estrogen receptor and androgen receptor positive and progesterone receptor negative, but exceptionally showed human epidermal growth factor receptor 2 gene amplification. Mastermind-like transcriptional coactivator 2 gene translocations were not detected by fluorescent in situ hybridization. The patient received adjuvant chemotherapy with anti-human epidermal growth factor receptor 2 therapy but no endocrine therapy. After 61 months of follow-up, no signs of local or distant recurrence were observed. CONCLUSIONS: Mucoepidermoid carcinoma of the breast is a very rare entity. Despite being most frequently triple negative, the standard evaluation of receptor status is mandatory, as well as strict application of World Health Organization diagnostic criteria for correct patient management.

Secretory carcinoma of salivary glands with NTRK3 break-apart molecular rearrangement: Potential misdiagnosis with mucoepidermoid carcinoma.

A woman presented a right submandibular gland lesion with cytologic diagnosis of mucoepidermoid carcinoma. Patient underwent sialoadenectomy en bloc with supraomohyoid neck dissection. Positivity for ETV6-NTRK3 genes fusion on surgical sample led to final diagnosis of secretory carcinoma (SC). Secretory carcinoma has been renamed by WHO in 2017 from mammary-analogue-secretory carcinoma (MASC). Only 649 have been reported until 2019. While cytologic alteration are shared with other neoplasms as the acinic cell and mucoepidermoid carcinomas, ETV6-NTRK3 rearrangement is pathognomonic of SC. Although usually indolent and with low-stage presentation, SC has higher rate of local recurrences and nodal involvement than ACC. Surgical treatment represent the gold standard. Real prevalence of SC is probably underestimated due to the recent WHO 2017 reclassification. While cytologic analysis does not allow to discriminate SC from other malignancies, chromosomal examination is recommended. When low-grade SC is diagnosed, complete surgical resection assures good prognosis.

A case of lung carcinoma with a unique biphasic feature: Implications for histogenesis of "fake mucoepidermoid carcinoma" developing in the peripheral lung.

We present a case of lung carcinoma with a unique biphasic feature. The patient was a 67-year-old male smoker with idiopathic pulmonary fibrosis (IPF). A subpleural tumor in the left lower lobe, embedded in fibrotic tissue, was resected. Histologically, the tumor consisted of major and minor components of mucoepidermoid carcinoma (MEC) and surrounding conventional lepidic adenocarcinoma, respectively. Both components had the same TP53 somatic mutation (p.V157F) but not Mastermind-like 2 (MAML2) gene rearrangement. The two components may have developed from an identical origin. The tumor could be trans-differentiating from lepidic adenocarcinoma to MEC, possibly promoted by IPF-induced tissue damage. The final diagnosis was "adenosquamous carcinoma with mucoepidermoid-like features (that may originate from lepidic adenocarcinoma)." This case has implications for the potential histogenesis of peripheral lung MEC. Over time, the MEC would expand and outgrow the lepidic adenocarcinoma, making it impossible to distinguish between fake and true MEC. The present case suggests that peripheral MEC could differ from proximal MEC in its histogenesis and molecular genetics. Thus, careful examination is necessary to diagnose peripheral lung MEC, particularly in patients with interstitial lung diseases.

Salivary Gland Neoplasms With a Unique Trabecular Histology and MAML2 Translocation : A Trabecular Variant of a Mucoepidermoid Carcinoma.

Mucoepidermoid carcinomas (MECs) are the most common salivary gland malignancy and have a diverse histology. Many histologic variants of MEC have now been confirmed with characteristic molecular alterations involving CRTC1::MAML2 or CRTC1::MAML3 translocations. We here report a series of 7 trabecular variants of MEC which showed a predominant trabecular or nested pattern with either focal glandular differentiation or clear cell change and keloid-like fibrosis in the background. In addition, these tumors were either negative or showed only focal positivity for p63. Such features are not characteristic of known disease entities and resulted in an initial misdiagnosis of adenocarcinoma, not otherwise specified, or low-grade to intermediate-grade MEC with uncertainty. The patients' ages in our cohort ranged from 26 to 55 years with a female predominance (5/7). The tumors were located in the parotid gland (n=3), base of tongue (n=2), hard palate (n=1), and parapharyngeal space (n=1), with a median size of 1.5 cm. All 7 cases showed an MAML2 split pattern on fluorescence in situ hybridization analysis, and both RNA and whole-genome sequencing presented CRTC1::MAML2 translocation. All 7 cases showed a solid-predominant histology, and 3 cases displayed extracapsular extension. There were no other signs of high-grade histology and no recurrences or deaths occurred over a follow-up period of up to 79 months. We thus propose a unique trabecular variant of MEC that has atypical histologic and immunohistochemical features.

Primary mucoepidermoid carcinoma of the external auditory canal with a CRTC1::MAML2 fusion: A case report and a review of literature.

Mucoepidermoid carcinoma is a malignant neoplasm of exocrine glands that arises predominantly in salivary glands. It is seldom encountered as a primary cutaneous neoplasm, and in those patients, it often involves the external auditory canal. Given their rarity, they can pose a diagnostic challenge and prompt extensive workup. In salivary glands, mucoepidermoid carcinomas commonly harbor CRTC1/3::MAML2 fusions; however, genetic alterations of primary cutaneous neoplasms are less characterized, with previous studies reporting CRTC1 rearrangements in the absence of MAML2 aberrations. Herein, we report a case of a primary cutaneous mucoepidermoid carcinoma of the external auditory canal with a CRTC1::MAML2 rearrangement. We also review the clinical, morphologic, and molecular features of this neoplasm and compare them to those reported in the literature and to histopathologic mimics.

Rearrangement of KMT2A Characterizes a Subset of Pediatric Parotid Mucoepidermoid Carcinomas Arising Metachronous to Acute Lymphoblastic Leukemia.

Introduction: Metachronous mucoepidermoid carcinomas (MMEC) may occur in association with childhood leukemias and lymphomas. We compared molecular abnormalities of MMEC in patients with ALL with the abnormalities found in primary mucoepidermoid carcinomas (MECs) in pediatric cases and young adults. Materials and methods: Immunohistochemical stains for p63 and SOX10, molecular alterations in MAML2 and KMT2A genes detected by FISH and/or next-generation sequencing were studied in 12 pediatric MMECs secondary to ALL and six primary MECs in pediatric patients and young adults. Follow-up information of patients in both groups was obtained. Results: KMT2A rearrangements were detected in pediatric MMECs, and they were associated with remarkable histomorphological changes, including deposits of abundant stromal collagen and intratumoral lymphoid proliferations. No KMT2A rearrangements were found in primary MECs. The prognosis of MMEC in patients with ALL, especially in KMT2A-rearranged cases, was worse than in primary MECs. Kruskal-Wallis test showed a statistically significant difference in overall survival between KMT2A-rearranged MMECs and KMT2A-intact MMECs in cases with ALL (p = 0.027). Conclusion: KMT2A-rearranged MMECs in ALL patients may have inherently more aggressive behavior, even when the histomorphology of MMEC suggests a low-grade malignancy.

Warthin-like mucoepidermoid carcinoma of the parotid gland: Clinicopathological observation and literature review.

Warthin tumor (WT)-like mucoepidermoid carcinoma resembles the histologic pattern of WT and pathologists unaware of this possibility may misdiagnose it as WT with squamous and mucous epithelium metaplasia or WT malignant transfer into mucoepidermoid carcinoma. The present study reported a case of a 41-year-old Chinese female with a solitary mass in the left parotid gland. In this case, microscopic observation revealed prominent lymph node stroma and multiple cystic structures similar to those seen in WT. However, it lacked the two layers of oncocytic epithelial tissue characteristic of WT. Furthermore, fluorescence in situ hybridization detected MAML2 rearrangement in the case. Considering the histological findings, this case was diagnosed as WT-like mucoepidermoid carcinoma. The present case report provides pathological and clinical features to differentiate it from WT malignant transition into mucoepidermoid carcinoma, WT with squamous and mucous epithelium metaplasia and non-sebaceous lymphadenoma-like mucoepidermoid carcinoma. In conclusion, WT-like mucoepidermoid carcinoma as a special subtype of mucoepidermoid carcinoma has special histological characteristics, which required further observations and more case reports to clearly define this variant.

The molecular landscape of breast mucoepidermoid carcinoma.

Mucoepidermoid carcinoma (MEC) of the breast is an extremely rare salivary gland-type tumor characterized by epidermoid, basaloid, intermediate, and/or mucinous cells arranged in solid and cystic patterns. Despite their triple-negative phenotype, breast MECs are generally considered low-risk malignancies but their biology is largely unexplored; therefore, guidelines for clinical management are lacking. Here, we sought to characterize the molecular landscape of breast MECs. Thirteen cases were histologically reviewed, characterized for tumor-infiltrating lymphocytes (TILs), and were subjected to immunohistochemistry for programmed death-ligand 1 (PD-L1, clone 22C3), EGFR, and amphiregulin (AREG). Rearrangements in MAML2 and EWSR1 were investigated by fluorescent in situ hybridization. Targeted next-generation sequencing of 161 genes was performed on eight cases. Most MECs had low histological grade (n = 10, 77%), with the presence of TILs (n = 9/12; 75%) and PD-L1 combined positive score ranging from 10 to 20 (n = 4/6; 67%). All cases showed EGFR and AREG overexpression and were fusion negative. Enrichment of genetic alterations was observed in PI3K/AKT/mTOR and cell cycle regulation pathways, while only one case harbored TP53 mutations. This is the first study providing extensive molecular data on breast MECs and the largest collection of cases available to date in the literature. Breast MECs lack TP53 mutations found in high-grade forms of triple-negative breast cancers and MAML2 or EWSR1 rearrangements pathognomonic of salivary MECs. Triple-negativity and PD-L1 positivity suggest a window of opportunity for immunotherapy in these patients. The EGFR/AREG axis activation, coupled with the mutational patterns in PI3K/AKT/mTOR and cell cycle pathways warrants caution in considering MECs as low-risk neoplasms.

Clear-cell Variant of Mucoepidermoid Carcinoma Presenting as a Palatal Mass in a 10-Year-old Boy.

BACKGROUND: The clear-cell variant of mucoepidermoid carcinoma (MEC) involving minor salivary glands is extremely rare in children. CASE REPORT: We report a case of clear-cell variant MEC in the minor salivary gland in a 10-year-old boy who presented with a mass of the right hard palate. Fine-needle aspiration showed features suggestive of clear-cell variant of MEC. Microscopically, the tumor cells showed predominant clear cells and scattered mucous cells. There was increased mitotic activity (6/mm2). No tumor necrosis or nuclear pleomorphism was identified. The tumor cells were positive for cytokeratin 7 (CK7), tumor protein p63, P40 (ΔNp63), CK5/6 and mucicarmine. Rearrangement of mastermind-like transcriptional coactivator 2 (MAML2) (11q21) gene was present in the tumor cells by fluorescence in situ hybridization, supporting the diagnosis of an intermediate-grade clear-cell variant of MEC. A right infrastructure maxillectomy for palate carcinoma with negative margins was performed. Grossly, the tumor was a 2.1 cm well-circumscribed, friable, pale tan mass with focal areas of cystic change. The final pathological diagnosis was clear-cell variant of MEC, intermediate grade, pT2. Post surgery, the patient recovered and was doing well, with no tumor recurrence or metastasis at the 6-month follow-up. CONCLUSION: To the best of our knowledge, this is the first documented case of clear-cell variant MEC in a child. Due to low to intermediate tumor grade, an overtly aggressive treatment should be avoided in a child.

Primary Thyroid Mucoepidermoid Carcinoma (MEC) Is Clinically, Prognostically, and Molecularly Different from Sclerosing MEC with Eosinophilia: A Multicenter and Integrated Study.

Mucoepidermoid carcinoma (MEC) and sclerosing MEC with eosinophilia (SMECE) are rare primary thyroid carcinomas. In this study, we aimed to present our multicenter series of MEC and SMECE and integrated our data with published literature to further investigate the clinicopathological characteristics and prognoses of these tumors. We found 2 MECs and 4 SMECEs in our multicenter archives. We performed fluorescence in situ hybridization (FISH) to determine the MAML2 gene rearrangement. We screened for mutations in BRAF, TERT promoter, and RAS mutations using Sanger sequencing and digital polymerase chain reaction. Histopathologically, MECs and SMECEs were composed of two main cell types including epidermoid and mucin-secreting cells, arranged in cords, nests, and tubules. SMECEs were characterized by a densely sclerotic stroma with abundant eosinophils. We did not detect any MAML2 fusion in any of our cases. Two MEC cases harbored concomitant BRAF p.V600E and TERT C228T mutations. RAS mutations were absent in all cases. Concurrent foci of another thyroid malignancy were more commonly seen in MECs (p < 0.001), whereas SMECEs were associated with chronic lymphocytic thyroiditis (p < 0.001). MECs and SMECEs had equivalent recurrence-free survival (RFS) but MECs conferred significantly dismal disease-specific survival (DSS) as compared to SMECEs (p = 0.007). In conclusion, MECs and SMECEs not only shared some similarities but also demonstrated differences in clinicopathological characteristics, prognoses, and molecular profiles. SMECEs had a superior DSS in comparison to MECs, suggesting that they are low-grade cancers. This could help clinicians better evaluate patient outcomes and decide appropriate treatment plans.

Diagnostic Reliability of CRTC1/3::MAML2 Gene Fusion Transcripts in Discriminating Histologically Similar Intraosseous Mucoepidermoid Carcinoma from Glandular Odontogenic Cyst: A Systematic Review and Meta-analysis.

BACKGROUND: Intraosseous mucoepidermoid carcinoma (IMEC) and Glandular odontogenic cyst (GOC) are those two pathological entities causing diagnostic dilemma due to the histopathological similarity. An accurate distinction between the two entities is difficult as both presents with a common radiological and histological similarities. The aim of our systematic review was to establish the diagnostic reliability of CRTC1/3::MAML2 gene fusion for the distinction between IMEC and GOC. METHODS: A complete electronic literature search was made in MEDLINE by PubMed, Google Scholar, and EMBASE databases. Articles with keywords using molecular genetic findings of CRTC1/3::MAML2 gene fusion transcripts, IMEC and GOC were assessed and included for the systematic review. RESULTS: Twelve subgroups having both qualitative and quantitative analysis revealed CRTC1/3::MAML2 sensitivity of 100% and specificity of 70.59% in differentiating GOC and IMEC. Fixed-effects model confirmed translocation-negative cases to have a decreased risk of association with IMEC (combined odds ratio 8.770, 95% confidence interval - 2.45 to 31.45, p < 0.002). CONCLUSIONS: The current evidence supports that in all cases with positive gene fusion transcript of the CRTC1/3::MAML2 was specific for IMEC and was significantly differentiating it from GOC. Whereas cases of IMEC with negative gene fusion transcript pose diagnostic difficulty in differentiating from a GOC which is negative for CRTC1/3::MAML2 expression.

Overexpression of LAG3, TIM3, and A2aR in adenoid cystic carcinoma and mucoepidermoid carcinoma.

OBJECTIVE: Adenoid cystic carcinoma (AdCC) and mucoepidermoid carcinoma (MEC) are the two most frequent malignancies of salivary glands. This study aims to explore the expression and migration of LAG3, TIM3, and A2aR in AdCC and MEC, and the potential relationship with oncogenic signaling molecules and immunosuppressive cytokines. MATERIALS AND METHODS: Custom made human salivary gland tissue microarrays included 81 AdCCs, 52 MECs, 76 normal salivary glands (NSG), and 14 pleomorphic adenoma (PMA) samples. Immunohistochemical analysis of lymphocyte activation gene 3 (LAG3), T-cell immunoglobulin and mucin domain-containing protein 3 (TIM3), adenosine 2a receptor (A2aR), oncogenic phosphorylated S6 kinase (p-S6) and ERK1/2 (p-ERK1/2 ), and TGF-ß1 was performed with salivary gland tissue microarrays of human samples. The correlation of the immunostaining was analyzed based on a digital pathological system, and data were evaluated by hierarchical cluster. Further in vitro studies of knockdown immune checkpoints LAG3, TIM3, and A2aR were carried out by siRNA transfection. RESULTS: The expression levels of LAG3, TIM3, and A2aR were remarkably increased in AdCC and MEC, compared with NSG and PMA samples, but were independent of pathology grade. They were closely correlated with TGF-ß1, slightly related to p-ERK1/2 and p-S6. After the knockdown of immune checkpoints LAG3, TIM3, and A2aR, the migration of SACC-LM cell line was significantly reduced. CONCLUSIONS: These results suggested that LAG3, TIM3, and A2aR are overexpressed in AdCC and MEC, may promote migration of SACC-LM cell and correlated with TGF-ß1 and oncogenic signaling pathways.

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

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

[Salivary papillary cystic low-grade mucoepidermoid carcinoma and cystadenoma: a comparison of clinicopathological and genetic features].

Objective: To study the clinicopathologic and genetic features of papillary cystic low-grade mucoepidermoid carcinoma (LG-MEC) and cystadenoma. Methods: A retrospective review was performed on salivary gland tumor patients with papillary cystic architecture who presented to department of oral pathology, Peking University School and Hospital of Stomatology between January 2010 and June 2022. Among this cohort, there were 17 males and 17 females with a range age of 23-82 years [(55.6±14.6) years]. Diagnosis was confirmed by histological, immunohistochemistry (IHC) and fluorescence in situ hybridization (FISH) analysis. Finally, 15 papillary cystic LG-MEC and 19 cystadenoma patients were included in the present study. All patients were followed clinically and radiologically, and the duration of follow-up ranged from 1 to 141 months. Results: All neoplasms showed papillary proliferation with multilocular or giant cystic tumors. Papillary cystic LG-MEC was characterized by epidermoid cells, intermediate cell and mucous cells with multiple lining-layers. Papillary cystic LG-MEC had mild cellular atypia and a pushing infiltration. Cystadenoma was characterized by cuboidal, columnar and ciliated pseudostratified columnar lining epithelium. Squamous metaplasia, mucinous metaplasia and acidophilic degeneration could also be observed focally in cystadenoma. For IHC staining, papillary cystic LG-MEC showed diffusely and strongly positive for mucin 4 (MUC4) (15/15) and mucin 5 Subtype AC (MUC5AC) (4/15) in the epidermoid cells, intermediate cell and mucous cells. The epidermoid cells and intermediate cells were diffusely positive for p40 and p63. The Ki-67 index was about 10%-15% in LG-MEC. As a contrast, p40 (17/19) and p63 (14/15) were only detected in the basal cells of cystadenoma. Cystadenoma showed focal MUC5AC (4/19)expression and MUC4 (19/19)diffuse expression. In addition, the Ki-67 index was 5%-10% in cystadenoma. The MAML2 gene translocation was detected in 11 LG-MEC patients, but none in cystadenoma. Conclusions: The differential diagnosis points between papillary cystic LG-MEC and cystadenoma included the specific epidermoid cells, intermediate cells and mucus cells in LG-MEC, cell atypia, the pushing-infiltration pattern, diffuse expression of p40 and p63 in the lining epithelium, and a MAML2 gene rearrangement. The molecular test of MAML2 should be recommended to reduce missed LG-MEC diagnoses.