A novel fusion gene CRTC3-MAML2 in hidradenoma: histopathological significance

Ancillary immunohistochemical and molecular testing in the classification of cutaneous sweat gland/duct neoplasms: A validation study with emphasis on histomorphologic correlation and pathological diagnosis

Sweat gland neoplasms represent a challenging area of dermatopathology, as they are relatively uncommon and often histopathologically complex. Recent studies have uncovered distinct immunohistochemical and molecular profiles in several sweat gland neoplasms, including digital papillary adenocarcinoma (DPA), papillary eccrine adenoma/tubular apocrine adenoma (PEA/TAA), poroid family tumors (PFT)/porocarcinoma, and clear cell hidradenoma (CCH)/clear cell hidradenocarcinoma (CCHCa). To further evaluate the diagnostic utility of ancillary studies in various sweat gland neoplasms, we performed an independent validation study in a cohort of patients with acral and non-acral tumors (9 DPA, 8 PEA/TAA, 13 PFT, 5 porocarcinoma, 23 CCH, 7 CCHCa, 6 sweat gland carcinoma not otherwise specified). p63 immunohistochemistry (IHC) demonstrated a myoepithelial pattern in 8/8 DPA and 4 of 4 tested PEA/TAA cases, and showed a ductal pattern in all tested PFT/porocarcinoma and CCH/CCHCa cases (42/42). All PEA/TAA (8/8) cases were positive for BRAF V600E IHC. 5 of 12 tested PFT and 5/5 porocarcinoma cases showed either positive staining with NUT IHC or harbored YAP1::NUTM1 fusion gene by RNA sequencing. MAML2 fluorescence in situ hybridization (FISH) was positive in all CCH and CCHCa cases (23/23 and 7/7, respectively). Our results further support the usefulness of appropriate ancillary studies in precise classification of sweat gland tumors, which may be routinely applied in diagnostic pathology practice when morphologic evaluation is in doubt.

[Cutaneous adnexal tumours: Development and synthesis of diagnostic fusion genes]

Cutaneous adnexal tumours are a heterogeneous group of epithelial lesions that includes tumours with follicular, sudoral and/or sebaceous differentiation, or even several combined lines of differentiation. Over the last few years, molecular analysis of these lesions has allowed to identify specific molecular events responsible for tumour development in an increasing number of tumour types. Like other rare neoplasms, such as soft tissue tumours, adnexal tumours display fusion genes resulting from chromosomal translocations that may be specific for the diagnosis if molecular data are properly integrated in the clinical and morphological setting. Molecular testing of adnexal tumours is valuable as it allows to strengthen the robustness of the diagnosis for a group of tumours displaying a wide morphological spectrum. It has allowed to refine the diagnostic criteria and to develop increasingly specific diagnostic immunostainings. Finally, molecular testing has been responsible for the identification of new entities or morphological subtypes of previously known entities. The aim of this review is to provide an update on cutaneous adnexal tumours associated with fusion genes and to evaluate the impact of molecular data on the diagnosis of these lesions.

Primary cutaneous apocrine carcinoma with RARA::NPEPPS fusion

Gene fusions have emerged as crucial molecular drivers of oncogenesis in a subset of cutaneous adnexal neoplasms, including poroid neoplasms and hidradenomas. We present a unique case of primary cutaneous apocrine carcinoma harboring RARA::NPEPPS fusion, broadening the spectrum of fusion-associated cutaneous adnexal neoplasms. A 77-year-old African American male presented with an ulcerated thigh nodule. Histopathologically, the predominantly dermal-based adenocarcinoma exhibited papillary, micropapillary, cribriform, and solid growth patterns with central comedonecrosis, set in a fibrotic/desmoplastic stroma. Immunophenotypically, the neoplastic cells were positive for CK7, CK19, GATA3, TRPS1, HER2, CK5/6, calretinin, p63, and DPC4 (no loss), while lacking immunoreactivity for CK20, CDX2, TTF1, napsin-A, PAX8, arginase-1, adipophilin, NKX3.1, uroplakin II, and D2-40. The immunoprofile and clinical and radiographic absence of any internal malignancy, including breast carcinoma, except for multiple lymphadenopathy, supported the diagnosis of primary cutaneous apocrine carcinoma. Next-generation sequencing unveiled the novel RARA::NPEPPS fusion, concurrent ERBB2 amplification, and multiple somatic mutations involving TP53, CDKN2A, BRCA2, PIK3CA, PIK3R1, and others. The patient developed widespread metastases within a year after the initial diagnosis, indicating the tumor's aggressive behavior. This novel fusion, unprecedented in any human malignancies including primary cutaneous adnexal carcinomas, may suggest a potential new subtype within primary cutaneous adnexal carcinoma.

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.

Gene fusions in poroma, porocarcinoma and related adnexal skin tumours: An update

Poroma is a benign sweat gland tumour showing morphological features recapitulating the superficial portion of the eccrine sweat coil. A subset of poromas may transform into porocarcinoma, its malignant counterpart. Poroma and porocarcinoma are characterised by recurrent gene fusions involving YAP1, a transcriptional co-activator, which is controlled by the Hippo signalling pathway. The fusion genes frequently involve MAML2 and NUTM1, which are also rearranged in other cutaneous and extracutaneous neoplasms. We aimed to review the clinical, morphological and molecular features of this category of adnexal neoplasms with a special focus upon emerging differential diagnoses, and discuss how their systematic molecular characterisation may contribute to a standardisation of diagnosis, more accurate classification and, ultimately, refinement of their prognosis and therapeutic modalities.

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.

Strategic Approach to Heterogeneity Analysis of Cutaneous Adnexal Carcinomas Using Computational Pathology and Genomics

Cutaneous adnexal tumors are neoplasms that arise from skin appendages. Their morphologic diversity and phenotypic variability with rare progression to malignancy make them difficult to diagnose and classify, and there is currently no established treatment strategy. To overcome these difficulties, this study investigated the transcription factor SOX9 expression, morphology, and genetics of skin adnexal tumors for understanding their biology, especially their histogenesis. We showed that cutaneous adnexal tumors and their nontumor counterparts of skin and appendages exhibit expression patterns similar to that of SOX9. Its expression intensity and pattern, as well as histopathologic evaluation of tumors, were analyzed using digital images of 69 normal skin adnexal 9-type organs and 185 skin adnexal 29-type tumors as references. It was possible to distinguish basal cell carcinoma from squamous cell carcinoma, sebaceous carcinoma, and pilomatrixoma with significant differences, along with porocarcinoma from squamous cell carcinoma. Furthermore, unsupervised machine learning "computational pathology" was used to derive a multiregion whole-exome sequencing fusion method termed "genocomputed pathology." The genocomputed pathology of three representable adnexal carcinomas (porocarcinoma, hidradenocarcinoma, and spiradenocarcinoma) was evaluated for total nine cases. We showed that there was more heterogeneity than expected within the tumors as well as the coexistence of components lacking driver fusion genes. The presence or absence of potential driver genes, such as PIK3CA, YAP1, and PTEN, in each region was identified, highlighting a therapeutic strategy for cutaneous adnexal carcinoma encompassing heterogeneous tumors.

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.

Genetic and Immunohistochemical Profiling of Mammary Hidradenoma and Comparison to Mucoepidermoid Carcinoma

Mucoepidermoid carcinoma (MEC) is exceedingly rare in the breast, with <45 cases reported in the literature. Although estrogen receptor/progesterone receptor/human epidermal growth factor 2 triple-negative, MEC is characterized as a special subtype of breast carcinoma with significantly better prognosis than conventional basal-type tumors. Cutaneous hidradenoma (HA) is considered a benign adnexal neoplasm showing histomorphologic overlap with MEC. Rare cases of HA have also been reported in the breast, but these are relatively uncharacterized. In this study, we examined the clinicopathologic, immunohistochemical (IHC), and genetic features of 8 breast HAs, in comparison to 3 mammary MECs. All cases were positive for MAML2 break-apart fluorescence in situ hybridization. Eight cases demonstrated a CRTC1::MAML2 fusion, and one MEC harbored a CRTC3::MAML2 fusion; the latter is a novel finding in the breast. Mutational burden was very low, with only one HA exhibiting a MAP3K1 pathogenic alteration. By IHC, both MEC and HA demonstrated cell type-dependent expression of high- and low-molecular-weight keratins and p63, as well as negative to low-positive estrogen receptor and androgen receptor. Smooth muscle myosin and calponin highlighted an in situ component in the 3 cases of MEC; expression of these myoepithelial markers was negative in HAs. Additional distinguishing characteristics included the growth pattern and tumor architecture, the presence of glandular/luminal cells in HA, and overall higher IHC expression of SOX10, S100 protein, MUC4, and mammaglobin in MEC. Morphologic findings were also compared to a series of 27 cutaneous nonmammary HAs. Mucinous and glandular/luminal cells were identified in significantly more mammary HAs than nonmammary lesions. The findings provide insight into the pathogenesis of MAML2-rearranged neoplasms of the breast, underscore the overlapping genetic features of MEC and HA, and highlight similarities to their extramammary counterparts.

Genetics of adnexal tumors: An update

Cutaneous adnexal tumors form a vast heterogeneous group that include frequent entities that are mostly benign, as well as rare tumors that are occasionally malignant. In contrast to cutaneous tumors arising from the interfollicular epidermis that develop as a result of accumulation of UV-induced DNA damage (basal cell carcinoma, squamous cell carcinoma), the oncogenesis of adnexal tumors is related to a broad spectrum of genetic mechanisms (e.g., point mutation, fusion genes, viral integration, etc.). In this setting, specific and recurrent genetic alterations have been progressively reported, and these allow better classification of these entities. For certain of them, immunohistochemical tools are now available, enabling precise integrated histological and molecular diagnosis since certain entities are linked to well-defined alterations. In this context, we aim in this review to summarize the main molecular tools currently available for the classification of adnexal tumors.

The Challenge of "Monomorphic" Mucoepidermoid Carcinoma-Report of a Rare Case with Pure Spindle-Clear Cell Morphology

BACKGROUND

Mucoepidermoid carcinoma is a malignant salivary gland tumor which, in most cases, is composed of variable proportions of mucous, epidermoid, and intermediate cells.

METHODS

We report a case of parapharyngeal mucoepidermoid carcinoma with highly unusual ("monomorphic") light microscopic features as well as atypical immunohistochemical properties. Molecular analysis was performed using the TruSight RNA fusion panel.

RESULTS

The tumor featured heretofore undescribed histopathological features: sheets and nests composed of monomorphic neoplastic (plump spindle to epithelioid) cells with no mucous, intermediate, glandular/columnar, or any other cell type identified. The neoplastic cells displayed variable clear cell change and only expressed cytokeratin 7. Despite this non-classical morphology, the presence of the classical CRTC1::MAML2 fusion was demonstrated.

CONCLUSIONS

Mucoepidermoid carcinoma featuring a uniform ("monomorphic") population of neoplastic cells is a novel observation. A confident diagnosis of mucoepidermoid carcinoma can be made upon detection of the CRTC1/3::MAML2 fusion. Our case increases the spectrum of histopathological appearances that mucoepidermoid carcinoma may display.

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

INTRODUCTION

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

METHODS

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

RESULTS

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

CONCLUSION

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

Two distinct pathogenic pathways of digital papillary adenocarcinoma - BRAF mutation or low-risk HPV infection

Digital papillary adenocarcinoma (DPA) is a rare neoplasm that can exhibit local recurrence and distant metastasis. We present a series of eight cases of DPA showing two distinct clinical presentations, morphologies, immunophenotypes, and molecular features. Four cases were characterized by painless, slow-growing nodules located on the digits. The lesions were small, well-defined, and confined in the dermis. Histopathologically, these tumors were composed of glandular structures lined by cuboidal epithelium with luminal papillary infoldings. Only rare mitotic figures and minimal squamoid differentiation were present, and cellular necrosis was absent. All four cases were positive for the BRAF V600E immunohistochemistry but negative for p16, low-risk and high-risk HPV in situ hybridization (ISH). In contrast, the remaining four cases were characterized by painful, rapidly growing masses on the digits. These four lesions were located in the deep dermis and consisted of a solid, tightly packed papillary architecture lined by atypical epithelioid cells with inconspicuous nucleoli. Cellular necrosis, numerous mitotic figures, and prominent squamoid differentiation were seen. All cases were negative for the BRAF V600E IHC. However, they showed strong, patchy to diffuse reactivity for p16 and were positive for low-risk HPV ISH and negative for high-risk HPV ISH. Our findings suggest that the current classification of DPA encompasses tumors that show two discrete pathogenic pathways - BRAF mutation or low-risk HPV infection. DPAs with low-risk HPV infection exhibit aggressive clinical features, high-grade morphology, marked squamoid differentiation, and wild-type BRAF. DPAs with BRAF V600E have less aggressive clinical features, low-grade morphologic findings, mild to absent squamoid differentiation, and negative HPV infection.

Atypical Nodular Hidradenoma Versus Low-Grade Hidradenocarcinoma in a Young Female Patient: A Case Report and Review of Literature

The objective of this study was to discuss an unusual postauricular mass in a pediatric patient. This mass had a broad differential including congenital anomaly, neoplasm, infection, and lymphovascular malformation. Atypical nodular hidradenoma is a rare adnexal tumor that is difficult to differentiate from hidradenocarcinoma. It is a rare entity, but especially rare in the pediatric population. This study aims to provide guidance on diagnosing hidradenoma and distinguishing it from hidradenocarcinoma through case presentation with a review of the literature. The patient in this report underwent wide location resection with close surveillance and has been disease-free during follow-up.

Clinicopathological and genomic copy number variation analysis in nodular hidradenoma and hidradenocarcinoma with focus on prognostically important features

Nodular hidradenoma is a cutaneous adnexal tumor of sweat gland origin, characterized by its diverse but overlapping histomorphologic features with other skin tumors. In addition, distinction of benign hidradenoma and its malignant counterpart hidradenocarcinoma can be challenging, especially in prognostic prediction. We retrospectively reviewed pathological features of 29 cases, including benign nodular hidradenoma (n = 17) and hidradenocarcinoma (n = 12), with clinical follow-up ranging from 18 to 216 months. Genomic copy number variation (CNV) was studied in selected cases (n = 18) by single nucleotide polymorphism microarray. None of the benign hidradenomas (0/17) or low-grade hidradenocarcinomas (0/6) had recurrence or metastasis after complete excision, whereas all 6 high-grade hidradenocarcinomas (6/6) showed locally destructive disease, recurrence, or local metastases. In benign hidradenomas, CNV abnormality was absent in all clear cell hidradenomas (0/5) but was detected in a considerable portion of poroid hidradenoma (3/5), with number of abnormalities ranging 2, 4, and 9. In malignant cases, regardless of morphological classification, both low-grade hidradenocarcinomas demonstrated limited CNV abnormalities in 2 areas (2/2), whereas all high-grade hidradenocarcinomas contained 8 or more CNV abnormalities (6/6). No disease-associated death was recorded in the cohort except one case was lost to follow-up after the development of metastatic disease. Overall, the findings support that genomic CNV abnormalities may serve as a sensitive but less specific tool in detecting malignancy in these tumors, and potentially have a role in predicting clinical behavior particularly in the tumors of nonporoid morphology.

MAML2 Gene Rearrangement Occurs in Nearly All Hidradenomas: A Reappraisal in a Series of 20 Cases

ABSTRACT

Hidradenoma is a benign cutaneous adnexal neoplasm that occurs across a wide age range and at a variety of anatomic sites. Its most characteristic morphologic feature is the presence of diverse cell types including squamoid, clear, plasmacytoid, and mucinous cells. Hidradenoma is morphologically and molecularly similar to mucoepidermoid carcinoma, and both tumors are characterized by recurrent CRTC1-MAML2 cytogenetic translocations. Previous studies have suggested that approximately half of hidradenomas possess this translocation. This finding raised the question of whether translocation-negative hidradenomas might have an alternate molecular basis. Here, we sought to reevaluate the frequency of MAML2 translocation in hidradenoma in a series of 20 cases. We find that 90% show evidence of MAML2 translocation, suggesting that this genetic event is a nearly invariant feature of hidradenoma. These results inform our molecular understanding of this tumor and may be useful in challenging cases to distinguish hidradenoma from its histologic mimics.

MAML2-Rearranged Mucoepidermoid Carcinoma of the Parotid Gland: A Report in a 20-Month-Old Toddler

Malignancies of salivary gland origin are rare in children. Mucoepidermoid carcinoma (MEC) is the most common histologic type of salivary gland neoplasm in pediatrics. We report a rare case of parotid MEC in a 20-month-old female patient. The tumor was composed of nests of epidermoid cells with nuclei appearing vesicular, pleomorphic, and hyperchromatic with an admixture of mucous cells and cystic spaces within a prominent connective tissue stroma. Immunohistochemically, the epidermoid cells showed cytokeratin 7 and P63 positivity, and mucous cells were positive for mucicarmine. Molecularly, this case was positive for MAML2 rearrangement by FISH. To our knowledge, this is one of the youngest cases of MEC of the parotid gland reported in the English literature.

Molecular pathology of skin adnexal tumours

AIMS

Tumours of the cutaneous adnexa arise from, or differentiate towards, structures in normal skin such as hair follicles, sweat ducts/glands, sebaceous glands or a combination of these elements. This class of neoplasms includes benign tumours and highly aggressive carcinomas. Adnexal tumours often present as solitary sporadic lesions, but can herald the presence of an inherited tumour syndrome such as Muir-Torre syndrome, Cowden syndrome or CYLD cutaneous syndrome. In contrast to squamous cell carcinoma and basal cell carcinoma, molecular changes in adnexal neoplasia have been poorly characterised and there are few published reviews on the current state of knowledge.

METHODS AND RESULTS

We reviewed findings in peer-reviewed literature on molecular investigations of cutaneous adnexal tumours published to June 2021.

CONCLUSIONS

Recent discoveries have revealed diverse oncogenic drivers and tumour suppressor alterations in this class of tumours, implicating pathways including Ras/MAPK, PI3K, YAP/TAZ, beta-catenin and nuclear factor kappa B (NF-κB). These observations have identified novel markers, such as NUT for poroma and porocarcinoma and PLAG1 for mixed tumours. Here, we provide a comprehensive overview and update of the molecular findings associated with adnexal tumours of the skin.

Clear Cell Proliferations of the Skin: A Histopathologic Review

ABSTRACT

Cutaneous clear cell proliferations encompass a heterogenous group of several primary cutaneous neoplasms and metastatic tumors with different histogenesis. Many of these clear cell proliferations may seem strikingly similar under the microscope resulting in challenging diagnosis. In many of these clear cell lesions, the reason for the clear or pale appearance of proliferating cells is unknown, whereas in other ones, this clear cell appearance is due to intracytoplasmic accumulation of glycogen, mucin, or lipid. Artifacts of tissue processing and degenerative phenomenon may also be responsible for the clear cell appearance of proliferating cells. Awareness of the histopathologic findings as well as histochemical and immunohistochemical techniques are crucial to the accurate diagnosis. This review details the histopathologic features of clear cell cutaneous proliferations, classifying them according their type of differentiation and paying special attention to the histopathologic differential diagnosis among them.

Update on Molecular Genetic Alterations of Cutaneous Adnexal Neoplasms

Cutaneous adnexal tumors recapitulate follicular, sweat gland, and/or sebaceous epithelia, and range from benign tumors to aggressive carcinomas. Adnexal tumors can be hallmarks for inherited tumor syndromes. Oncogenic drivers of adnexal neoplasms modulate intracellular pathways including mitogen-activated protein kinase, phosphoinositide-3-kinase, Wnt/β-catenin, Hedgehog, nuclear factor κB, and Hippo intracellular signaling pathways, representing potential therapeutic targets. Malignant progression can be associated with tumor suppressor loss, especially TP53. Molecular alterations drive expression of specific diagnostic markers, such as CDX2 and LEF1 in pilomatricomas/pilomatrical carcinomas, and NUT in poromas/porocarcinomas. In these ways, improved understanding of molecular alterations promises to advance diagnostic, prognostic, and therapeutic possibilities for adnexal tumors.

Poroid adnexal skin tumors with YAP1 fusions exhibit similar histopathologic features: A series of six YAP1-rearranged adnexal skin tumors

BACKGROUND

Adnexal skin tumors are diagnostically challenging with few known molecular signatures. Recently, however, YAP1-MAML2 and YAP1-NUTM1 fusions were identified in poroid adnexal skin tumors.

METHODS

Herein, we subjected eight poroid adnexal skin tumors (three poromas and five porocarcinomas) to fusion gene analysis by whole transcriptome sequencing and next-generation DNA sequencing analysis.

RESULTS

YAP1 fusions were identified in six cases. YAP1-NUTM1 fusions were identified in two poromas and three porocarcinomas. A single case of porocarcinoma harbored a YAP1-MAML2 fusion. Two cases were negative for gene fusion. All cases that harbored YAP1-NUTM1 fusions showed nuclear protein in testis (NUT) expression by immunohistochemistry, with NUT being negative in the YAP1-MAML2-positive case. In this case series, we provide a detailed histopathologic description of six YAP1-fused poroid skin tumors, which we show harbor reproducible histopathologic features, to include broad, bulbous tumor tongues with admixtures of basaloid, poroid cells punctuated by squamatized cuticles and ductules, with uniform tumor nuclei featuring frequent grooves and pseudonuclear inclusions.

CONCLUSIONS

Awareness of the characteristic histopathologic features of YAP1-fused poroid adnexal skin tumor is a step toward a more reproducible classification of adnexal skin tumors as well as a step toward targeted therapy for metastatic and/or unresectable examples of this poroid group of neoplasms.

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

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

NUT Is a Specific Immunohistochemical Marker for the Diagnosis of YAP1-NUTM1-rearranged Cutaneous Poroid Neoplasms

YAP1-NUTM1 fusion transcripts have been recently reported in poroma and porocarcinoma. NUTM1 translocation can be screened by nuclear protein in testis (NUT) immunohistochemistry in various malignancies, but its diagnostic performance has not been thoroughly validated on a large cohort of cutaneous epithelial neoplasms. We have evaluated NUT immunohistochemical expression in a large cohort encompassing 835 cases of various cutaneous epidermal or adnexal epithelial neoplasms. NUT expression was specific to eccrine poromas and porocarcinoma, with 32% of cases showing NUT expression. All other cutaneous tumors tested lacked NUT expression, including mimickers such as seborrheic keratosis, Bowen disease, basal cell carcinoma, squamous cell carcinoma, Merkel cell carcinoma, nodular hidradenoma, and all other adnexal tumors tested. Remarkably, NUT expression was more frequent in a distinct morphologic subgroup. Indeed, 93% of poroid hidradenoma (dermal/subcutaneous nodular poroma, 13/14) and 80% of poroid hidradenocarcinoma cases (malignant poroid hidradenoma, 4/5) showed NUT expression, in contrast to 17% and 11% of classic poroma (4/23) and porocarcinoma cases (4/35), respectively. RNA sequencing of 12 NUT-positive neoplasms further confirmed the presence of a YAP1-NUTM1 fusion transcript in all cases, and also an EMC7-NUTM1 gene fusion in a single case. In the setting of a cutaneous adnexal neoplasm, nuclear expression of NUT accurately and specifically diagnosed a specific subgroup of benign and malignant poroid tumors, all associated with a NUTM1 fusion, which frequently harbored a poroid hidradenoma morphology.

Effects of the MAML2 genetic variants in glioma susceptibility and prognosis

BACKGROUND

Abnormal expression of the mastermind-like transcriptional co-activator 2 (MAML2) gene is oncogenic in several human cancers, including glioma. However, the relevance of MAML2 variants with glioma remains unknown. We aimed to investigate the role of MAML2 polymorphisms in glioma risk and prognosis among the Chinese Han population.

METHODS

Seven MAML2 single-nucleotide polymorphisms (SNPs) were genotyped using Agena MassARRAY system among 575 patients with glioma and 500 age- and gender-matched healthy controls. Logistic regression was used to estimate the association between MAML2 polymorphisms and glioma risk by calculating odds ratios (ORs) and 95% confidence intervals (CI). Kaplan-Meier survival analysis and univariate, multivariate Cox proportional hazard regression analyses for hazard ratios (HRs) and 95% CIs were performed to evaluate the contribution of MAML2 polymorphisms to glioma prognosis.

RESULTS

MAML2 rs7938889 and rs485842 polymorphisms were associated with the reduced risk of glioma (OR = 0.69, P=0.023; and OR = 0.81, P=0.032, respectively). Rs7115578 polymorphism had a lower susceptibility to glioma in males (OR = 0.68, P=0.034), while rs4598633 variant with a higher risk in females (OR = 1.66, P=0.016). Additionally, rs7115578 AG genotype represented a poorer prognosis of glioma (HR = 1.24, P=0.033) and astrocytoma (log-rank P=0.037, HR = 1.31, P=0.036). Furthermore, rs11021499 polymorphism had lower overall survival (OS) and progression-free survival (PFS) in patients with low-grade glioma.

CONCLUSION

We provided some novel data suggesting MAML2 polymorphisms might contribute to glioma risk and prognosis. Future studies are warranted to validate these findings and characterize mechanisms underlying these associations.

Clinicopathologic Characterization of Hidradenoma on Acral Sites: A Diagnostic Pitfall With Digital Papillary Adenocarcinoma

Hidradenomas are benign sweat gland tumors that typically present as small nodules in adulthood. Their anatomic distribution is wide and rarely includes acral sites. In this setting, reliable separation from digital papillary adenocarcinoma is important, but notoriously difficult. Hematoxylin and eosin-stained sections of 25 hidradenomas on acral skin were retrieved. The clinical presenting features and morphologic findings were recorded, and follow-up was obtained. Immunohistochemistry was performed for AE1/3, CK5/6, EMA, CEA, SMA, S100, p40, and p63. The tumors presented as solitary nodules on the hands (n=17) and feet (n=8) of adults (age range: 20 to 81 y; median: 50 y), with an equal sex distribution. Histologically, the well-circumscribed tumors were lobular, with a solid and cystic growth within dermis. Duct and squamous differentiation and vascularized hyaline stroma were frequent. The majority (n=18) were poroid hidradenomas. Scattered cytologic atypia and mitotic activity (median: 2/10 HPF) were common, and a pseudoinfiltrative growth of strands in a hyaline to sclerotic matrix was noted in 5 tumors. No papillary structures, atypical mitoses, or tumor necrosis were present. Immunohistochemically, all tumors expressed AE1/3, CK5/6, p40, and p63 strongly and diffusely. Luminal differentiation was highlighted by epithelial membrane antigen and carcinoembryonic antigen staining. S100 and SMA staining was absent. Follow-up (1 to 288 mo; median: 61 mo), available for 20 patients, showed no local recurrences and no disease-related mortality. Acral hidradenomas and digital papillary adenocarcinomas share a well-circumscribed dermal growth pattern containing solid, cystic, and tubular areas with mitotic activity and at least focal cytologic atypia. Lack of papillary structures and the diffuse positivity for p40 and p63 in the absence of S100 and SMA expression are helpful features in favor of acral hidradenoma.

Next-generation sequencing implicates oncogenic roles for p53 and JAK/STAT signaling in microcystic adnexal carcinomas

Microcystic adnexal carcinoma is a locally aggressive sweat gland carcinoma characterized by its infiltrative growth and histopathologic overlap with benign adnexal tumors, often posing challenges to both diagnosis and management. Understanding the molecular underpinnings of microcystic adnexal carcinoma may allow for more accurate diagnosis and identify potential targetable oncogenic drivers. We characterized 18 microcystic adnexal carcinomas by targeted, multiplexed PCR-based DNA next-generation sequencing of the coding sequence of over 400 cancer-relevant genes. The majority of cases had relatively few (<8) prioritized somatic mutations, and lacked an ultraviolet (UV) signature. The most recurrent mutation was TP53 inactivation in four (22%) tumors. Frame-preserving insertions affecting the kinase domain of JAK1 were detected in three (17%) cases, and were nonoverlapping with TP53 mutations. Seven (39%) cases demonstrated copy number gain of at least one oncogene. By immunohistochemistry, p53 expression was significantly higher in microcystic adnexal carcinomas with TP53 mutations compared with those without such mutations and syringomas. Similarly, phospho-STAT3 expression was significantly higher in microcystic adnexal carcinomas harboring JAK1 kinase insertions compared with those with wild-type JAK1 and syringomas. In conclusion, microcystic adnexal carcinomas are molecularly heterogeneous tumors, with inactivated p53 or activated JAK/STAT signaling in a subset. Unlike most other nonmelanoma skin cancers involving sun-exposed areas, most microcystic adnexal carcinomas lack evidence of UV damage, and hence likely originate from a relatively photo-protected progenitor population in the dermis. These findings have implications for the biology, diagnosis, and treatment of microcystic adnexal carcinomas, including potential for therapeutic targeting of p53 or the JAK/STAT pathway in advanced tumors.

Genetic variant of MAML2 in the NOTCH signaling pathway and the risk of bladder cancer: A STROBE-compliant study

The NOTCH signaling pathway plays a crucial role in cell phenotype and transformation. Single nucleotide polymorphisms (SNPs) may regulate gene expression to trigger bladder cancer susceptibility. Here, we aimed to explore the relationships between genetic variants in the NOTCH pathway and bladder cancer progression.We screened SNPs located in NOTCH pathway genes using the 1000 Genomes Project dataset (CHB). A case-control cohort study including 580 bladder cancer cases and 1101 controls was conducted to genotype the candidate SNPs. The expression quantitative trait locus (eQTL) and bioinformatics analyses were performed to explore the biological function of the SNPs' host gene and their relationship. Kaplan-Meier analysis was performed to assess the association between host gene expression and bladder cancer patient prognosis.The rs7944701 in the intron of mastermind-like 2 (MAML2) had the strongest signal and was related to bladder cancer risk (OR = 1.329, 95% CI = 1.115-1.583, P = .001). eQTL analysis showed that rs7944701 with a C allele was negatively associated with mastermind-like 2 (MAML2) expression (TT versus TC/CC). Bioinformatics analysis indicated that MAML2expression was lower in bladder cancer tissues than in non-tumor tissues (P = 5.46 × 10). Additionally, bladder cancer patients with high MAML2 expression had a significantly poorer prognosis (HR = 1.53, 95% CI = 1.29-1.82, P = .010).The rs7944701 in MAML2 was strongly associated with bladder cancer susceptibility in a Chinese population. This genetic variant and its host gene could be a potential novel biomarker for individuals suffering from bladder cancer.

"Pancreatic Mucoepidermoid Carcinoma" Is not a Pancreatic Counterpart of CRTC1/3-MAML2 Fusion Gene-related Mucoepidermoid Carcinoma of the Salivary Gland, and May More Appropriately be Termed Pancreatic Adenosquamous Carcinoma With Mucoepidermoid Carcinoma-like Features

"Mucoepidermoid carcinoma (MEC)" has been accepted as a synonym for pancreatic adenosquamous carcinoma (ASC). Pancreatic ASC can show salivary gland-type MEC-like morphology. CRTC1/3-MAML2 fusion gene is a characteristic molecular feature of MEC of the salivary gland. We conducted this study to clarify whether the pancreatic ASC with salivary gland-type MEC-like morphology (Pan-MEC) is a pancreatic counterpart of salivary gland-type MEC (Sal-MEC). We retrospectively analyzed 37 pancreatic ASCs including 16 Pan-MECs and 21 tumors without MEC-like features (ASC-NOS [not otherwise specified]), and we investigated (1) clinicopathologic features, (2) the presence of CRTC1/3-MAML2 fusion gene by reverse transcription polymerase chain reaction, (3) the presence of rearrangement of MAML2 gene by fluorescence in situ hybridization, and (4) mucin core proteins by immunohistochemistry. We also compared 16 Pan-MECs with 20 Sal-MECs by immunohistochemistry for mucin core protein. There were no significant differences of any clinicopathologic characteristics and survival analysis between the Pan-MECs and ASCs-NOS. Of note, the pancreatic ASCs (including Pan-MEC and ASC-NOS) were significantly more aggressive than conventional pancreatic ductal adenocarcinoma. In addition, all Pan-MECs were histologically high-grade. CRTC1/3-MAML2 fusion gene and MAML2 gene rearrangement were not detected in any ASCs including Pan-MECs. There were significant differences of MUC5AC and MUC6 between the Pan-MECs and Sal-MECs, but no significant differences of mucin core protein between the Pan-MECs and pancreatic ASCs-NOS. Pan-MEC is histologically and biologically high-grade and unrelated to CRTC1/3-MAML2 fusion gene, unlike Sal-MEC which is related to CRTC1/3-MAML2 fusion gene. Pan-MEC is not a pancreatic counterpart of CRTC1/3-MAML2 fusion gene-related Sal-MEC.