Pathologic characteristics of NUT midline carcinoma arising in the mediastinum. Am J Surg Pathol. 2012;36:1222-1227. [PMID: 22790861 DOI: 10.1097/pas.0b013e318258f03b]

Molecularly Defined Thoracic Neoplasms

Molecularly defined neoplasms are increasingly recognized, given the broader application and performance of molecular studies. These studies allow us to better characterize these neoplasms and learn about their pathogenesis. In the thorax, molecularly defined neoplasms include tumors such as NUT carcinoma, SMARCA4-deficient undifferentiated tumor (DUT), primary pulmonary myxoid sarcoma with EWSR1::CREB1 fusion, hyalinizing clear cell carcinoma, and SMARCB1-deficient neoplasms. Overall, these tumors are rare but are now more often recognized given more widely available immunostains such as NUT (NUT carcinoma), BRG1 (SMARCA4-DUT), and INI-1 (SMARCB1-deficient neoplasm). Furthermore, cytogenetic studies for EWSR1 to support a hyalinizing clear cell carcinoma or primary pulmonary myxoid sarcoma are, in general, easily accessible. This enables pathologists to recognize and diagnose these tumors. The diagnosis of these tumors is important for clinical management and treatment. For instance, clinical trials are available for patients with NUT carcinoma, SMARCA4-DUT, and SMACRB1-deficient neoplasms. Herein, our current knowledge of clinical, morphologic, immunophenotypic, and molecular features of NUT carcinomas, SMARCA4-DUT, primary pulmonary myxoid sarcomas, hyalinizing clear cell carcinoma, and SMARCB1-deficient neoplasms will be reviewed.

Nuclear Protein in Testis (NUT) Carcinoma: A Comprehensive Immunohistochemical Analysis of 57 Cases With Consideration of Interpretation and Pitfall Recognition

CONTEXT.—

Nuclear protein in testis (NUT) carcinoma is an aggressive carcinoma defined by NUTM1 gene rearrangement. Diagnostic challenges include morphologic overlap with poorly differentiated squamous cell carcinoma, small cell carcinoma, thoracic SMARCA4-deficient undifferentiated tumor, and other small round blue cell tumors.

OBJECTIVE.—

To comprehensively study the immunohistochemistry (IHC) features of a large cohort of NUT carcinomas.

DESIGN.—

Fifty-seven NUT carcinoma cases were identified from 2012-2022, including 38 thoracic/mediastinal, 13 head and neck/sinonasal, and 6 from other sites. Pathology reports and available slides were reviewed. Comprehensive IHC studies were performed on available cases.

RESULTS.—

Keratin stains showed variable positivity and were entirely negative in 15% (8 of 55) of cases. p40 was only positive in 65% (24 of 37) of cases, implying inferior sensitivity when compared to p63 (87% sensitivity, 20 of 23 cases) and other squamous cell markers. Neuroendocrine markers were focally/weakly positive in few cases; however, INSM1 was positive in 54% (7 of 13) of cases, indicating a possible diagnostic pitfall. TTF-1 was mostly negative with focal positivity in 26% (10 of 38) of cases. Occasional CD34 (15%, 3 of 20 cases) and CD99 (21%, 3 of 14 cases) positivity could also cause potential diagnostic confusion. S100, desmin, CD45, and SALL4 were rarely positive. BRG1 and INI1 were retained in all cases. Ki-67 proliferative index was high (median, 60%). PD-L1 was negative in all tested cases.

CONCLUSIONS.—

This comprehensive IHC study demonstrates the immunohistochemical spectrum of NUT carcinoma. The findings can help narrow the differential diagnosis and recognize potential pitfalls.

A Novel NUTM1-NSMCE2 Fusion Gene in a Pediatric Chest NUT Carcinoma

Nuclear protein of the testis carcinoma is an exceedingly rare and poorly differentiated carcinoma characterized by BDR4::NUTM1 gene translocation. Typically, the tumor affects young adults, and no standardized recommendations for therapeutic management have been available since 2022; the clinical course remains mostly dismal. We report the successful multimodal treatment of a 13-year-old boy affected by a primary chest NUT-carcinoma with a novel NUTM1 rearrangement that remains in complete continuous remission at 30 months from diagnosis.

Oral and oropharyngeal NUT carcinoma: a multicentre screening study of poorly differentiated oral cancer

BACKGROUND AND AIMS

Nuclear protein testis (NUT) carcinoma (NC) is a rare and highly aggressive tumour characterised by chromosomal rearrangement of the nuclear protein testis family member 1 (NUTM1) gene, also known as the NUT gene. NC occurs mainly in the head and neck, mediastinum and lung. In general, primary NC in the oral cavity is extremely rare and reported sporadically.

METHODS

A total of 111 formalin-fixed and paraffin-embedded specimens of poorly differentiated oral and oropharyngeal tumours were collected from 10 hospitals. NUT protein IHC staining was performed on these samples, and fluorescence in-situ hybridisation (FISH) and RNA sequencing detection were further carried out for NUT IHC-positive cases.

RESULTS

The expression of NUT protein in tumour cells was detected in five cases (five of 111, 4.5%). The tumours in these cases were located in the oral floor, lip, base of the tongue, gingiva and hard palate. FISH detection results showed BRD4::NUT rearrangement in three patients and a non-BRD4::NUT rearrangement pattern in two patients. RNA sequencing results confirmed BRD4::NUT rearrangement in two cases.

CONCLUSIONS

To our knowledge, this is the first and largest retrospective study of oral NC, and we found that NC is easily misdiagnosed as poorly differentiated oral squamous cell carcinoma (SCC) or poorly differentiated carcinoma. The morphology and immunophenotype of four NC cases were similar to SCC, and abrupt keratinisation was observed in three cases. Therefore, it is necessary to detect NUT protein for NC screening in oral malignant tumours with these morphologies, especially for young patients who are more likely to be misdiagnosed with other types of cancer.

Utility of Immunohistochemistry in the Diagnosis of Pleuropulmonary and Mediastinal Cancers: A Review and Update

CONTEXT.—

Immunohistochemistry has become a valuable ancillary tool for the accurate classification of pleuropulmonary and mediastinal neoplasms necessary for therapeutic decisions and predicting prognostic outcome. Diagnostic accuracy has significantly improved because of the continuous discoveries of tumor-associated biomarkers and the development of effective immunohistochemical panels.

OBJECTIVE.—

To increase the accuracy of diagnosis and classify pleuropulmonary neoplasms through immunohistochemistry.

DATA SOURCES.—

Literature review and the author's research data and personal practice experience.

CONCLUSIONS.—

This review article highlights that appropriately selecting immunohistochemical panels enables pathologists to effectively diagnose most primary pleuropulmonary neoplasms and differentiate primary lung tumors from a variety of metastatic tumors to the lung. Knowing the utilities and pitfalls of each tumor-associated biomarker is essential to avoid potential diagnostic errors.

Neuroendocrine and squamous cell phenotypes of NUT carcinoma are potential diagnostic pitfalls that discriminating it from mimickers, such as small cell and squamous cell carcinoma

INTRODUCTION

NUT carcinoma is a rare cancer associated with a poor prognosis. Because of its rarity, its diagnosis is challenging and is usually made by excluding other diagnoses. Immunohistochemical analysis is a reliable technique that contributes to a correct diagnosis, but overestimating the expression of neuroendocrine (NE) markers may result in an incorrect diagnosis. In this study, we established the immunohistochemical phenotypes of NUT carcinoma compared with tumors that mimic its phenotype to identify potential diagnostic pitfalls.

METHODS

Eight cases of NUT carcinoma were examined along with eight basaloid squamous cell carcinomas and thirteen cases of small cell carcinoma using an immunohistochemical panel consisting of various antibodies.

RESULTS

Of the eight NUT carcinomas, three patients had a smoking history. All the cases examined for INSM1 were positive (6/6, 100%), although the staining was somewhat weak. Among the NE markers, synaptophysin was variably positive in two NUT carcinomas (2/6, 33%); however, all cases were negative for ASCL1, chromogranin A, and CD56. Moreover, the squamous cell markers, p40 and CK5/6, were weakly expressed in 4/6 (67%) and 3/6 (50%) of the NUT carcinomas, respectively.

CONCLUSIONS

For tumors with an ambiguous morphology, applying the neuroendocrine phenotype of NUT carcinoma may be misleading; particularly, when distinguishing it from small-cell carcinoma. Similarly, null or weak expression of squamous cell markers may be observed in NUT carcinoma, but this differs from squamous cell carcinoma, which consistently demonstrates strong positivity for squamous cell markers.

Thymic epithelial tumours: histopathological classification and differential diagnosis

The epithelial and lymphoid compartments of the thymus can give rise to a wide variety of tumours, including thymomas, thymic carcinomas, lymphoreticular proliferations, germ cell tumours, and sarcomas. While some of these have close similarity to their counterparts in other organs, both in terms of histology and immunohistochemistry, as well as molecular features, others are unique to the thymus. The epithelial tumours, which can develop in the thymus, will be discussed in this review, with a particular emphasis on resolving differential diagnosis by means of morphology, immunohistochemical profiles, and molecular diagnostics.

NUT carcinoma and thoracic SMARCA4-deficient undifferentiated tumour: facts and controversies

NUT carcinoma and thoracic SMARCA4-deficient undifferentiated tumour are unique entities in the 5th edition of the World Health Organisation (WHO) Classification of Thoracic Tumours, whose definitions include molecular genetic abnormalities. These aggressive tumours require rapid work-ups on biopsies, but a broad list of differential diagnoses poses challenges for practising pathologists. This review provides an update on their key clinicopathological and molecular characteristics, as well as controversies regarding tumour classification and diagnostic strategy. Phenotypical assessment plays a substantial role in diagnosis because recurrent and predictable clinicopathological findings exist, including robust immunohistochemical phenotypes. Accurate diagnosis is crucial for appropriate management and a clearer understanding of the disease.

MRI Findings and Differential Diagnosis of Anterior Mediastinal Solid Tumors

The anterior mediastinum is the most common location of mediastinal tumors, and thymic epithelial tumors are the most common mediastinal tumors. It is important to differentiate thymic epithelial tumors from malignant lymphomas and malignant germ cell tumors because of the different treatment strategies. Dynamic contrast-enhanced MRI and diffusion-weighted imaging can provide additional information on the differential diagnosis. Chemical shift imaging can detect tiny fat tissues in the lesion and is useful in differentiating thymic hyperplasia from other solid tumors such as thymomas. MRI findings reflect histopathological features of mediastinal tumors, and a comprehensive evaluation of MRI sequences is important for estimation of the histopathological features of the tumor. In this manuscript, we describe the MRI findings of anterior mediastinal solid tumors and the role of MRI in the differential diagnosis.

Role of radiotherapy in the management of rare solid thoracic tumors of the adults

Thoracic tumors include more than one hundred histopathological subtypes. Rare thoracic malignancies can be defined as representing less than 1% of all thoracic tumors. The European Rare Cancer Surveillance Project (RARECARE) identified rarity as an incidence less than 6 for 100,000 people, with significant difference of prevalence between them. Modalities of treatment for these pathologies include surgery, radiotherapy, and systemic therapies. In this article, we aim to discuss role and techniques of radiotherapy in management of rare solid thoracic tumors in adults, focusing on different anatomical locations such as lung parenchyma, mediastinum, vessels, chest wall and pleural cavity.

Diagnosis of thoracic SMARCA4-deficient undifferentiated tumor in cytology

INTRODUCTION

Although alterations in SMARCA4-deficient occur in non-small cell lung carcinoma (SD-NSCLC), thoracic SMARCA4-deficient undifferentiated tumor (TSDUT) is recognized as a distinct entity in the 2021 World Health Organization Classification of Thoracic Tumors because of unique morphologic, immunophenotypic and molecular features, and worse survival compared with SD-NSCLC. Cytologic diagnosis of TSDUT is clinically important because of its aggressive behavior and because it is often diagnosed by fine-needle aspiration because TSDUTs are usually unresectable at presentation. Here, we identify cytologic features that can be used for recognition of TSDUT and distinction from SD-NSCLC.

MATERIALS AND METHODS

Cytomorphologic features were investigated in cytology specimens from patients with TSDUT (n = 11) and compared with a control group of patients with SD-NSCLC (n = 20).

RESULTS

The presence of classic rhabdoid morphology, at least focally, was entirely specific for TSDUT (n = 6, 55%) compared with SD-NSCLC (n = 0) in this study. TSDUT more frequently showed tumor necrosis (n = 11, 100% vs. n = 8, 40%; p = .001), dominant single-cell pattern on aspirate smears or touch preparation slides (n = 8 [of 9], 80% vs. n = 3, 15%; p = .010), nuclear molding (n = 5, 45% vs. n = 1, 5%; p = .013), and indistinct cell borders (n = 11, 100% vs. n = 5, 25%; P < .001) compared with SD-NSCLC, respectively.

CONCLUSIONS

Cytomorphologic features occurring more frequently in TSDUT include tumor necrosis, dominant single-cell pattern, nuclear molding indistinct cell borders, and focal rhabdoid cells. Presence of these features in a cytology specimen of an undifferentiated tumor, particularly in a patient with a thoracic mass, should raise suspicion for TSDUT and prompt appropriate ancillary workup.

Primary pulmonary NUT midline carcinoma: An elusive and a rare diagnostic entity

Nuclear protein in testis (NUT) midline carcinoma is a poorly differentiated tumor, is more common in midline anatomic sites, and involves young adults and children mainly. Primary pulmonary NUT midline carcinoma (NMC) is a rare and poorly defined entity in the prevailing literature. Being a highly aggressive and fatal neoplasm, it gets incumbent for the oncologists and the pathologists to be aware of this entity as it holds distinct management protocol and prognosis. Currently, BET inhibitors (BETi) and histone deactylase inhibitors have shown promising results as targeted therapies in clinical trials in head and neck NMC. We present a case report of NMC of primary pulmonary location in a young male with widespread bony metastasis.

Clinical and molecular features of pulmonary NUT carcinoma characterizes diverse responses to immunotherapy, with a pathologic complete response case

PURPOSE

Nuclear protein in testis (NUT) carcinoma is an uncommon malignant cancer characterized by NUTM1 rearrangement. We aimed to investigate the clinicopathological and molecular features and immunotherapy of pulmonary NUT carcinoma.

METHODS

Immunohistochemistry (IHC) for NUT (C52B1) and programmed cell death ligand 1 (PD-L1: 22C3) and fluorescence in situ hybridization (FISH) for NUTM1 break and BRD4-NUTM1 fusion were performed on six pulmonary NUT carcinoma samples.

RESULTS

The 6 pulmonary NUT carcinoma samples were obtained from 5 males and 1 female, with ages ranging from 31 to 73 years (average, 46 years). Five tumors occurred in the lobes, with one in the trachea. Pathologically, all cases showed primitive-appearing round to epithelioid cells growing in nests and sheets. Squamous differentiation and abrupt keratinization were observed. All tumors expressed the NUT protein and p63, and 4 tumors showed focal synaptophysin, but PD-L1 expression was not observed. All cases displayed NUTM1 rearrangement, 5 had BRD4-NUTM1 fusion, and one had an unknown partner. Three patients presented regional lymph node involvement at diagnosis. Five patients underwent intensive radiation and/or chemotherapy. Furthermore, 2 patients (1 and 2) received a combination of PD-L1 inhibitor and chemotherapy. Patient 1 exhibited a poor response and soon showed tumor progression and metastasis; however, patient 2 responded remarkably and achieved pathologic complete response (pCR) without uncontrollable adverse events. The overall survival time was 2.9 months.

CONCLUSIONS

Pulmonary NUT carcinoma exhibits poorly differentiated morphological features with diffuse NUT staining, low PD-L1 expression, and NUTM1 rearrangement. Despite its poor prognosis, it presents a diverse response to immunotherapy. Immune checkpoint inhibitors (ICIs) need to be further explored in NUT carcinoma.

NUT Carcinoma in Children and Adolescents: The Expert European Standard Clinical Practice Harmonized Recommendations

BACKGROUND AND AIMS

Nuclear protein of the testis (NUT) carcinoma (NC) is a rare and highly aggressive tumor mainly occurring in adolescents and young adults, defined by the presence of a somatic NUTM1 rearrangement. The aim is to establish internationally harmonized consensus recommendations for the diagnosis and treatment of adolescents and young adults with NC in the framework of the European Reference Network for Paediatric Oncology.

METHODS

The European Cooperative Study Group for Pediatric Rare Tumors developed recommendations according to the Consensus Conference Standard Operating procedure methodology and reviewed by external "experts." No evidence of level I to II exists. Recommendations were developed based on published prospective (level III), but more frequently retrospective series (level IV), case reports (level V), and personal expertise (level V). In addition, "strength" of recommendations were categorized by grading (grade A to E).

RESULTS

Histology is mandatory for the diagnosis of NC, including immunolabeling with anti-NUT antibodies and molecular biology (NUTM1 rearrangement) (level V; grade A). Treatment of NC usually combines aggressive approaches in multimodal regimens. Chemotherapy should be considered as first-line treatment (neoadjuvant vincristine-adriamycin-ifosfamide/cisplatin-adriamycin-ifsofamide or vincristine-doxorubicin-cyclophosphamide/ifosfamide-etoposide) for unresectable or metastatic tumor (ie, 3 courses), rapidly followed by local treatment (level IV; grade B). Referral to a specialized surgical oncology center is highly recommended (level V; grade A). In localized NC, a complete microscopic surgical resection should be attempted whenever and as soon as possible, followed by primary irradiation (60 to 70 Gy) and involved lymph nodes area (level IV; grade B). For head and neck tumors, a systematic neck dissection might be considered, even if N0 (level V; grade C). Adjuvant postirradiation chemotherapy is recommended, for a total of 9 to 12 courses (level IV; grade B). For first-line resected tumors, concomitant adjuvant chemotherapy to radiotherapy may be discussed (level IV; grade B). Targeted therapies and immunotherapeutic regimens should be delivered in the setting of prospective trials (level V; grade B).

CONCLUSIONS

This project leads to a consensus strategy based on international experience with this very rare disease.

NUT Carcinoma—An Underdiagnosed Malignancy

NUT carcinoma (NC) is a rare and highly aggressive malignancy with a dismal prognosis and a median survival of 6–9 months only. Although very few cases of NC are reported each year, the true prevalence is estimated to be much higher, with NC potentially widely underdiagnosed due to the lack of awareness. NC primarily occurs in midline structures including thorax, head, and neck; however, other sites such as pancreas and kidney are also affected, albeit at lower frequencies. NC is characterized by a single translocation involving the NUTM1 (NUT midline carcinoma family member 1) gene and different partner genes. The resulting fusion proteins initiate tumorigenesis through a mechanism involving BET (bromo-domain and extra-terminal motif) proteins such as Bromodomain-containing protein 4 (BRD4) and inordinate acetylation of chromatin, leading to the dysregulation of growth and differentiation genes. While no clinical characteristics are specific for NC, some histologic features can be indicative; therefore, patients with these tumor characteristics should be routinely tested for NUTM1. The diagnosis of NC using immunohistochemistry with a highly specific antibody is straightforward. There are currently no standard-of-care treatment options for patients with NC. However, novel therapies specifically addressing the unique tumorigenic mechanism are under investigation, including BET inhibitors. This review aims to raise awareness of this underdiagnosed cancer entity and provide all patients the opportunity to be properly diagnosed and referred to a clinical study.

Nuclear protein of the testis midline carcinoma of the thorax

Nuclear protein of the testis (NUT) midline carcinoma (NMC) is a rare tumor that typically presents in the head, neck, and chest region. NMC is characterized by rearrangement of the NUTM1 gene. It mainly affects children and young adults and is rapidly progressive and lethal. Reportedly, the prognoses of NMCs of the head and neck improve following aggressive initial surgical resection +/- postoperative chemoradiotherapy (CRT) or radiotherapy (RT). However, as NMC of the thorax was identified later, treatments to improve its prognosis are yet to be identified. Our review reveals that NMC is an extremely rare cancer, and most patients remain undiagnosed. Furthermore, this review outlines the clinical characteristics of NMC of the thorax and the prospects for its treatment.

NUT carcinoma of the thorax in a 7-year-old child

We present a rare case of NUT midline carcinoma of the thorax in a 7-year-old-male who presented with nonspecific abdominal pain. The patient was initially evaluated with an abdominal ultrasound, which was negative, followed by an abdominopelvic CT that demonstrated a partially visualized infiltrative mediastinal mass. Subsequent, chest CT showed a large, aggressive appearing heterogenous middle mediastinal mass with pulmonary parenchyma, hilar, and posterior mediastinal invasion. Given its epicenter in the middle mediastinum and its irregular and invasive appearance, the primary consideration was NUT midline carcinoma, subsequently confirmed on biopsy.

Immunotherapy in head and neck squamous cell carcinoma and rare head and neck malignancies

The dismal prognosis of recurrent/metastatic (R/M) head and neck squamous cell carcinoma (HNSCC) prompted recent advances in the field of therapeutic approaches beyond cytotoxic cancer therapy. In recent years, the deeper and increasing knowledge on the genomic landscape and the upcoming new data on immunotherapy enacted by HNSCCs have led to successful therapeutic targeting of the immune system. Immune checkpoint inhibitors (ICIs) have changed state of the art in R/M patients and could have a potential role even in early disease. The purpose of this work is to summarize the role of immunotherapy for R/M HNSCC in clinical practice, with insights about future perspectives. Updated immunotherapy results in other R/M head and neck cancers such as thyroid, salivary glands, nasopharynx, sinonasal cancers, and nuclear protein in testis (NUT) are presented.

Thymic tumours and their special features

Thymic tumours are rare thoracic malignancies, that may be aggressive and difficult to treat. The pillars of the management include pathological review, consideration of differential diagnoses, staging and multidisciplinary discussion. Assessment of resectability is key to drive the treatment sequencing. Association with autoimmune diseases, especially myasthenia gravis, is observed, which impacts the oncological management. Networks are being built at the national and international levels. This article provides an overview of the most recent findings in the diagnosis, staging, histology, and management strategies of thymic tumours.

Thymic tumours are rare and heterogeneous tumours. Management is based on multidisciplinary discussion and networking.https://bit.ly/3kYAZ7u

NUTM1-Rearranged Neoplasms-A Heterogeneous Group of Primitive Tumors with Expanding Spectrum of Histology and Molecular Alterations-An Updated Review

Nuclear protein of testis (NUT), a protein product of the NUTM1 gene (located on the long arm of chromosome 15) with highly restricted physiologic expression in post-meiotic spermatids, is the oncogenic driver of a group of emerging neoplasms when fused with genes involved in transcription regulation. Although initially identified in a group of lethal midline carcinomas in which NUT forms fusion proteins with bromodomain proteins, NUTM1-rearrangement has since been identified in tumors at non-midline locations, with non-bromodomain partners and with varied morphology. The histologic features of these tumors have also expanded to include sarcoma, skin adnexal tumors, and hematologic malignancies that harbor various fusion partners and are associated with markedly different clinical courses varying from benign to malignant. Most of these tumors have nondescript primitive morphology and therefore should be routinely considered in any undifferentiated neoplasm. The diagnosis is facilitated by the immunohistochemical use of the monoclonal C52 antibody, fluorescence in situ hybridization (FISH), and, recently, RNA-sequencing. The pathogenesis is believed to be altered expression of oncogenes or tumor suppressor genes by NUT-mediated genome-wide histone modification. NUTM1-rearranged neoplasms respond poorly to classical chemotherapy and radiation therapy. Targeted therapies such as bromodomain and extraterminal domain inhibitor (BETi) therapy are being developed. This current review provides an update on NUTM1-rearranged neoplasms, focusing on the correlation between basic sciences and clinical aspects.

NUT Carcinoma: A Clinical, Morphological and Immunohistochemical Mimicker-The Role of RNA Sequencing in the Diagnostic Procedure

Background: NUT carcinoma is a highly aggressive and rare subset of squamous cell carcinoma with grim prognosis. It is under-recognized by both pathologists and oncologists. Recognition is challenging due to its rareness and the fact that its clinical and laboratory features as well as morphological and immunohistochemical characteristics may mimic other malignancies. Case presentation: An interesting case of NUT carcinoma in a 47-year-old male with a large tumor mass in the inferior part of the mediastinum and left lung and increased levels of serum alpha fetoprotein (AFP) is described. Immunohistochemical analysis of both the primary tumor in a bronchoscopy specimen and an excisional biopsy of a subcutaneous metastasis showed positivity for AFP and leukocyte common antigen (LCA) that were misleading and resulted in diagnostic pitfalls of mediastinal germ cell tumor (clinically) and hematolymphoid neoplasm (pathologic report). Immunohistochemical demonstration of NUT protein expression revealed the proper diagnosis, which was further confirmed by RNA sequencing revealing a BRD4-NUTM1 gene fusion.Conclusions: Since NUT carcinoma can show a wide spectrum of histological and immunophenotypic features and can clinically mimic other tumors, use of RNA sequencing with identification of specific NUTM1 fusion partner could be crucial when there are discrepant clinical and histopathological findings. As well, since the category of so-called NUTM1-rearranged neoplasms is rapidly expanding, identification of NUTM1 fusion partner may be essential for the appropriate clinical management.

Diagnostic Challenges in Fine-Needle Aspiration Cytology of Mediastinal Tumors and Lesions

CONTEXT.—

Mediastinal tumors/lesions are frequently encountered in daily cytopathology practice. These lesions are accessible through endoscopic/endobronchial ultrasound-guided or computed tomography-guided fine-needle aspiration cytology and represent a wide range of primary and metastatic tumors. This often poses diagnostic challenges because of the complexity of the mediastinal anatomic structures. Tumors metastatic to mediastinal lymph nodes represent the most common mediastinal lesions and must be differentiated from primary lesions.

OBJECTIVE.—

To provide an updated review on the fine-needle aspiration cytology of mediastinal tumors/lesions, with an emphasis on diagnostic challenges. This review encompasses thymic epithelial neoplasms, mediastinal lymphoproliferative disorders, germ cell tumors, neuroendocrine tumors, soft tissue tumors, and metastatic tumors. Differential diagnoses; useful ancillary studies, including targeted immunohistochemical panels; and diagnostic pitfalls are discussed.

DATA SOURCES.—

Data were gathered from a PubMed search of peer-reviewed literature on mediastinal tumors. Data were also collected from the authors' own practices.

CONCLUSIONS.—

Fine-needle aspiration cytology plays a vital role in evaluation of mediastinal lesions. Being familiar with the clinical and cytomorphologic features of these lesions, appropriately triaging the diagnostic material for ancillary testing, and correlating with radiologic findings are important in arriving at correct diagnoses and guiding management.

Skin adnexal carcinoma with BRD3-NUTM2B fusion

NUT carcinomas are genetically defined epithelial neoplasms. Most tumors harbor fusions of NUTM1 with BRD4 or BRD3. Their histopathologic features have been predominantly reported as undifferentiated or poorly differentiated squamous cell carcinoma, and clinically they tend to be aggressive cancers. However, recent studies have revealed a broader spectrum of NUTM1-rearranged neoplasms with several new fusion partners and associated variable histopathologic phenotypes and clinical behaviors, including benign and malignant cutaneous poroid tumors. We report herein a primary invasive carcinoma of skin adnexal origin with a previously undescribed fusion between BRD3 and NUTM2B. The tumor occurred on the shoulder of a 7-year-old girl and was excised with negative margins. A sentinel lymph node was positive. After follow-up of 23 months, and without systemic treatment, the child remains free of tumor. This case expands the spectrum of NUT carcinomas by including a skin adnexal variant with follicular infundibular differentiation, a novel genomic aberration, and preliminary evidence of a less aggressive clinical course.

NUT carcinoma of the lung

NUT carcinoma of the thorax is a rare and very aggressive tumor, whose definition is based on the demonstration of a nuclear protein in testis (NUTM1; also known as NUT) gene fusion on 15q14 with different partners from the bromodomain-containing proteins gene family. This fusion results in an activation of MYC oncoprotein responsible for the tumor's aggressivity. NUT carcinoma arises preferentially in young adults, presenting a large thoracic mass frequently associated with lymph nodes, bone or pleural metastases. At histology, this tumor is often poorly differentiated, mainly composed of sheets of small cells with scant cytoplasm, a round nucleus with a central nucleolus. Focal areas of squamous differentiation can be observed. Mitoses and necrosis are frequent, as well as neutrophilic infiltrate. The diagnosis is based on the detection of NUT protein expression by immunohistochemistry using the rabbit monoclonal antibody C52B1 in more than 50% of the tumor nuclei. This technique offers 87% sensitivity and nearly 100% specificity with reference to FISH or RT-PCR, which confirm the NUTM1 rearrangement. The differential diagnoses include basaloid carcinoma of the lung, small cell carcinoma, thymic carcinoma (basaloid variant), SMARCA4_deficient thoracic sarcoma, other NUTM1 rearranged undifferentiated tumors, small round cell tumors, non-Hodgkin lymphoma/leukemia, and melanoma. The prognosis of NUT carcinoma remains very poor, with a median survival of 6.7 months, and 1- and 2-year overall survival rates of 30% and 19%, respectively. NUT carcinoma is often refractory to conventional chemotherapy, but ifosfamide-based regimens or BET inhibitors could represent promising therapies.

Thoracic NUT carcinoma: Common pathological features despite diversity of clinical presentations

NUT carcinoma (NC), formerly known as NUT midline carcinoma, is a rare and very aggressive cancer. It is genetically defined by the presence of acquired chromosomal rearrangement of the NUTM1 (NUclear protein in Testis Midline carcinoma family member 1) gene at chromosome 15q14 with a member of the bromodomain-containing protein (BRD) family gene, usually BRD4. Although primarily reported in the head and neck, and mediastinum locations of younger individuals, it is now established that NC arises in multiple sites in patients of all ages, with no gender predilection. NC is very likely to be underdiagnosed because of a lack of awareness of both clinicians and pathologists on the one hand, and of a nonspecific histological presentation on the other hand. As it is indistinguishable from other poorly differentiated carcinomas, pathologists should consider NC as a differential diagnosis of any poorly differentiated tumour. Diagnosis is now easily made by immunohistochemistry, using a highly sensitive and specific NUT monoclonal antibody. Despite chemo- or chemo-radiotherapy, the prognosis of this tumour remains very poor. We report here a series of 3 cases of NC with different clinical and pathological presentations in order to draw attention on some common morphological features that can help clinicians and pathologists to think about this rare entity.

GOECP/SEOR radiotherapy guidelines for thymic epithelial tumours

Thymic epithelial tumours (TET) are rare, heterogeneous neoplasms that range from resectable indolent tumours to aggressive thymic carcinomas with a strong tendency to metastasize. The pathological diagnosis is complex, in part due to the existence of several different classification systems. The evidence base for the management of TETs is scant and mainly based on non-randomised studies and retrospective series. Consequently, the clinical management of TETs tends to be highly heterogenous, which makes it difficult to improve the evidence level. The role of technological advances in the field of radiotherapy and new systemic therapies in the treatment of TETs has received little attention to date. In the present clinical guidelines, developed by the GOECP/SEOR, we review recent developments in the diagnosis and classification of TETs. We also present a consensus-based therapeutic strategy for each disease stage that takes into consideration the best available evidence. These guidelines focus primarily on the role of radiotherapy, including recent advances, in the management of TETs. The main aim of this document is to promote the standardisation of clinical practice and lay the foundations for future studies to clarify the main unresolved questions related to the optimal management of TET.

Thoracic nuclear protein in testis (NUT) carcinoma: expanded pathological spectrum with expression of thyroid transcription factor-1 and neuroendocrine markers

AIMS

Nuclear protein in testis (NUT) carcinoma, an aggressive tumour driven by NUTM1 rearrangements, often involves the lung/mediastinum and shows squamous differentiation. We encountered an index patient with a thoracic NUT carcinoma diagnosed by molecular testing, showing extensive pleural involvement and diffuse thyroid transcription factor-1 (TTF-1) expression, initially suggestive of lung adenocarcinoma with pseudomesotheliomatous growth. We thus gathered an institutional series of thoracic NUT carcinomas to examine their pathological spectrum.

METHODS AND RESULTS

We searched for thoracic NUT carcinomas in our surgical pathology files and in 2289 consecutive patients with primary thoracic tumours investigated with RNA-based assays. We performed NUT immunohistochemistry on 425 additional lung adenocarcinomas. Collectively, we identified six patients (five men and one woman; age 31-80 years; four never-smokers) with thoracic NUT carcinomas confirmed by molecular testing (including five with positive NUT immunohistochemistry). They died at 2.3-12.9 months (median, 2.8 months) after presentation. Two patients were diagnosed by histopathological assessment, and the remaining four (including the index patient) were diagnosed by molecular testing. Analysis of the index case revealed expression of multiple neuroendocrine markers and TTF-1; no ultrastructural evidence of neuroendocrine differentiation was noted. No additional NUT-positive cases were found by immunohistochemical screening.

CONCLUSIONS

Although NUT carcinoma classically shows squamous differentiation, it can rarely express TTF-1 (even diffusely) and/or multiple neuroendocrine markers. This immunophenotypic spectrum may lead to diagnostic confusion with pulmonary adenocarcinoma, neuroendocrine tumour, and others. To circumvent this pitfall, NUT immunohistochemistry and/or NUTM1 molecular testing should be considered in primitive-appearing tumours, regardless of their immunophenotypic features.

Comprehensive genetic profiling of six pulmonary nuclear protein in testis carcinomas with a novel micropapillary histological subtype in two cases

Nuclear protein in testis (NUT) carcinoma (NC) is a rare and aggressive neoplasm associated with a rearrangement of the NUT gene on chromosome 15q14. To date, genomic alterations of NCs, especially those in the lung, are poorly understood. In this study, immunohistochemistry staining, fluorescence in situ hybridization, and two next-generation sequencing (NGS) panels of 56 and 701 genes were used to explore the clinical, pathological, and genetic profiling of pulmonary NCs. Six pulmonary NC cases were confirmed, with a mean age of 41 years (range: 22-69 years) and a median survival time of 6.5 months (range: 2-19 months). Morphologically, typical abrupt keratinization was observed in four of six cases (67%), and two patients presented a mixed pattern of classical squamous component and micropapillary adenocarcinoma morphology. We also identified a case with NUT gene amplification instead of rearrangement. Furthermore, NGS analysis demonstrated the following fusions: BRD4-NUTM1 (2/4 cases) and NSD3-NUTM1 (2/4 cases), and the analysis highlighted 53 gene mutations, including 50 (94.3%, 50/53) single-nucleotide variations (SNVs) and three (5.7%, 3/53) long insertions/deletions. SNVs of MUC16 were the most common and occurred in three cases (75%). Moreover, SNVs of EPHA8, FANCA, TRIO, and USP6 were detected in two of four cases (50%). These 53 mutated genes were involved in 13 functional pathways based on enrichment analysis, especially in the PI3K-Akt signaling pathway. Finally, none of the cases showed obvious copy number variations and had low tumor mutational burden and stable microsatellite sites.

Common and rare carcinomas of the thymus

Thymic carcinoma encompasses a diverse group of rare tumors that occur almost exclusively in the prevascular (anterior) mediastinum. Thymic carcinomas have a worse outcome than thymomas with a median time to death of under 3 years. These tumors lack the typical lobulation of thymomas, exhibit commonly more cytologic atypia, are associated with a desmoplastic stromal reaction, and lack thymocytes, features that distinguish them from thymomas. The most common thymic carcinoma is squamous cell carcinoma; other subtypes include mucoepidermoid carcinoma, NUT carcinoma, and adenocarcinoma, among others. Largely due to multi-institutional and global efforts and meta-analysis of case reports and series, some of the thymic carcinoma subtypes have been studied in more detail and molecular studies have also been performed. Morphology and immunophenotype for the vast majority of thymic carcinoma subtypes are similar to their counterparts in other organs. Therefore, the distinction between thymic carcinoma and metastatic disease, which is relatively common in the prevascular mediastinum, can be challenging and in general requires clinical and radiologic correlation. Although surgical resection is the treatment of choice, only 46 to 68% of patients with thymic carcinoma can undergo resection as many other tumors present at high stage with infiltration into vital neighboring organs. These patients are usually treated with chemotherapy and/or radiation. The search for better biomarkers for prognosis and treatment of thymic carcinomas is important for improved management of these patients and possible targeted therapy.

NUT Carcinoma Arising from the Parotid Gland: A Case Report and Review of the Literature

NUT carcinoma is an aggressive carcinoma with an overall poor survival outcome. The mediastinum and head and neck area, especially the sinonasal region, are among the common sites of disease. Histopathological diagnosis of NUT carcinoma is often very challenging due to its overlapping features with other poorly differentiated carcinomas. We report a case of NUT carcinoma arising from the parotid gland of a young female patient. Primary NUT carcinoma of salivary gland is very rare, with only 15 such cases reported in the literature to date. Our case highlights the diagnostic challenges associated with such lesions.

Clinicopathological characteristics of primary lung nuclear protein in testis carcinoma: A single-institute experience of 10 cases

BACKGROUND

Nuclear protein in testis (NUT) carcinoma is a rare tumor associated with NUT rearrangement that can present as poorly differentiated to undifferentiated carcinoma, with or without abrupt squamous differentiation. It is often misdiagnosed as poorly differentiated carcinoma or undifferentiated carcinoma if NUT is not suspected. In this study, we retrospectively analyzed pulmonary NUT carcinoma cases diagnosed with NUT immunohistochemical staining and discuss the differential diagnosis to provide information for this rare and aggressive entity.

METHODS

Cases, diagnosed as "NUT carcinoma" in lung pleura and "metastatic NUT carcinoma from the lung" in lymph nodes were diagnosed between 2017 and 2019 at the Samsung Medical Center (SMC). Clinical features such as age, sex, treatment and follow-up period, and pathological reports were obtained by reviewing patients' electronic medical records.

RESULTS

A total of 10 NUT carcinoma cases were found in the SMC pathology database. Seven patients were men and six were non-smokers. Tumor cells showed various cellular features such as round, squamoid, and spindle. Some cases had initially been misdiagnosed as spindle cell neoplasm, round cell sarcoma, squamous cell carcinoma and small cell carcinoma. All cases showed diffuse strong nuclear expression of NUT immunohistochemical staining, and some were positive for p63 staining and negative for CD56 staining.

CONCLUSIONS

NUT carcinoma is often misdiagnosed because of its various morphologies. It is important to consider NUT as one of the differential diagnoses when encountering lung biopsy with undifferentiated morphology.

KEY POINTS

Due to various morphological features, NUT carcinoma can be misdiagnosed It is important to consider NUT carcinoma when diagnosing a poorly differentiated or undifferentiated tumor.

Advances in the pathogenesis and treatment of nut carcinoma: a narrative review

NUT carcinoma (NC) is a rare, highly invasive and fatal tumor and often misdiagnosed. It typically arises from the mediastinum and midline organs and has complicated pathogenesis and poor outcome. Genetically, its pathogenesis is related to a chromosomal rearrangement involving the NUTM1 gene. In most cases, the main oncoprotein is BRD4-NUT with a translocation between NUTM1 and BRD4 genes, but in a few cases, the oncoprotein is BRD3-NUT, or NSD3-NUT. Studies have shown that the histone hyperacetylation and BRD4 hyperphosphorylation may lead to the activation of cancer circuits. Abnormal production of microRNA, inactivation of tumor suppressor genes and abnormal activation of several signaling pathways are proposed as potential mechanisms underlying the pathogenesis of NC. Currently, there is no consensus on its standard treatment for NC. Extent of surgical resection with negative margins, initial radiotherapy and part of chemotherapy regimens may significantly associated with the improvement of progression-free survival (PFS) rate and overall survival (OS) rate. Some bromodomain and extraterminal inhibitors (BETis) have shown encouraging results in the clinical trials on NC, but delayed drug resistance is still an important issue that needs to be resolved. Histone deacetylase inhibitors are also found to possess the potential in the treatment of NC. Herein, we summarize recent advances in the pathogenesis and treatment of NC.

NUT Carcinoma in a Patient with Unusually Long Survival and False Negative FISH Results

Nuclear protein in testis (NUT) carcinoma is a rare and highly aggressive epithelial malignancy defined by rearrangement of the NUTM1 gene on chromosome 15q14. Histologically, NUT carcinoma is an undifferentiated carcinoma formed by sheets and nests of primitive and monotonous "round blue cells" with foci of abrupt keratinization in a subset. NUT carcinoma runs a fulminant clinical course and is almost always quickly lethal, with a median overall survival of only 6.7 months. There is no consensus regarding treatment for this disease, and most patients respond poorly to conventional chemotherapy and radiation. We report a case of NUT carcinoma in an African-American man who initially presented in 2009 with a tracheal mass at age 28. Although fluorescence in situ hybridization (FISH) assays for NUTM1 and BRD4 rearrangements were negative, he was diagnosed based on diffusely positive NUT immunostaining and BRD4-NUTM1 on RNA sequencing. Since his initial presentation, he has undergone multiple surgical procedures and radiation therapy. His tumor has recurred twice, but he has survived for 129 months and is currently alive without disease. Long-term survival of patients with NUT carcinoma is incredibly unusual, especially in patients with tumors that exhibit a BRD4 rearrangement. False negative FISH is a pitfall in diagnosing NUT carcinoma; NUT immunostaining and RNA sequencing are more sensitive diagnostic methods.

Clinical features, treatment, and survival outcome of primary pulmonary NUT midline carcinoma

Objective

NUT midline carcinoma (NMC), a rare type of squamous cell carcinoma, is genetically characterised by NUT midline carcinoma family member 1 (NUTM1) gene rearrangement. NMC can arise from the lungs; however, there is no standard for the management of primary pulmonary NMC. This study aimed to confirm the clinical features and report the treatments, especially with immune checkpoint inhibitors (ICIs), and outcomes of patients with primary pulmonary NMC.

Methods

A retrospective review of patients with primary pulmonary NMC was performed in the First Affiliated Hospital of Guangzhou Medical University between January 2015 and December 2018. Clinical manifestations as well as radiographic and pathological findings were recorded. Whole-exome sequencing (WES), a predictor for ICI response, was used to determine the tumour mutational burden (TMB). Treatments, especially by immune checkpoint blockade, and patient survival were analysed.

Results

Seven patients with primary pulmonary mass (four men and three women) with a mean age of 42 years (range, 23–74) who were diagnosed with NMC according to NUT immunohistochemistry staining were included for analysis. One patient had a rare fusion of CHRM5-NUTM1 by tumour sequencing. A wide range of TMB (1.75–73.81 mutations/Mbp) was observed. The initial treatments included chemotherapy (5/7, 71.4%), surgery (1/7, 14.3%), and radiotherapy (1/7, 14.3%). Five patients (5/7, 71.4%) received ICIs (programmed cell death protein 1 [PD1]/programmed cell death ligand 1 [PDL1] monoclonal antibody) as second- or higher-line treatments. The median overall survival (OS) was 4.1 months (range, 1.5–26.7 months).

Conclusions

Patients with primary pulmonary NMC have a poor prognosis and chemotherapy is often preferred. Checkpoint immunotherapy is a good option as the second- or higher-line treatment. TMB seems to be not associated with OS.

A Young Woman With a Rapidly Growing Thoracic Tumor

CASE PRESENTATION

A 38-year-old woman presented with 2 months of dry cough, progressive shortness of breath, central chest pain, nausea, vomiting, and dizziness. She was previously healthy and was not taking any medications. She denied fever, night sweats, or weight loss. She had a two pack-year smoking history and had quit smoking at 27 years of age. She denied drug use and had no recent travel history. Family history was pertinent for ovarian cancer, breast cancer, and colon cancer.

Salivary Gland NUT Carcinoma with Prolonged Survival in Children: Case Illustration and Systematic Review of Literature

NUT (midline) carcinoma is a rare, highly aggressive, poorly differentiated carcinoma that characteristically harbors a rearrangement of the NUTM1 gene. Most of these tumors occur in adolescents and young adults, arise from the midline structures of the thorax, head, and neck, and are associated with extremely poor outcomes. Rare cases originating from salivary glands have been reported with clinicopathologic features comparable to NUT carcinoma of other sites. Outcome studies regarding this subgroup are currently lacking. We report a case of NUT carcinoma arising in a submandibular gland of a 12-year-old boy. Diagnosis was confirmed by fluorescence in situ hybridization demonstrating fusion of the BRD4 (19p13.12) and NUTM1 (15q14) gene loci. A systematic review of all previously reported salivary gland NUT carcinomas (n = 15) showed exclusive occurrence of pediatric cases (n = 6) in males compared to adult patients (n = 9, male: female = 1:2; p < 0.05). The median survival was 24 and 4 months for pediatric and adult patients, respectively (95% confidence interval was 8-24 and 1-7 months, respectively; p < 0.01). The 1-year overall survival was 67% for pediatric and 11% for adult patients. Among all NUT carcinomas, pediatric salivary gland tumors may represent a distinct clinical subset associated with male predilection and comparatively prolonged survival.

Prevalence of NUT carcinoma in head and neck: Analysis of 362 cases with literature review

BACKGROUND

Nuclear protein in testis (NUT) carcinoma is a poorly differentiated carcinoma defined by the presence of NUT gene rearrangement. In the head and neck, the true prevalence of NUT carcinoma is unknown.

METHODS

We retrospectively investigated NUT expression with clinicopathologic features in 362 patients of poorly differentiated or undifferentiated carcinomas in the head and neck, and reviewed the literature reports.

RESULTS

Four (4/362, 1.1%) cases showed strong nuclear expression for NUT-specific monoclonal antibody, and all these tumors were in the sinonasal tract (4/40, 10%). The clinical outcome and histology were diverse unlike previously described. Although previous studies reported different frequency results according to study subjects, frequencies in sinonasal tract are relatively constant (10/80, 12.5%).

CONCLUSIONS

This is the largest study on the prevalence of NUT carcinoma in head and neck areas. It is important to include in the differential diagnosis of poorly differentiated carcinoma, particularly in the sinonasal tract.

The primary pulmonary NUT carcinomas and some uncommon somatic mutations identified by next-generation sequencing: a case report

Nuclear protein in testis (NUT) carcinoma (NUT-C) is an exceedingly rare and aggressive squamous tumor characterized by an acquired rearrangement of the NUT gene involving the NUTM1 (Nut midline carcinoma, family member 1, NUT) gene encoding the nuclear protein of the testis on 15q14. As a rare tumor, there is little information available on the clinicopathologic and molecular cytogenetic findings of NMC. We herein reported a case of a 69-year-old man diagnosed with lung NMC involving the rearrangement of chromosomal region 15q14 harboring the NUTM1 gene. It was exceptionally rare for the patient's involving of the lung but having the chance to be totally resected. After radical surgery, the patient accepted further four cycles of chemotherapy and remains disease-free after 10 months. The immunohistochemical staining of PDL1 was negative and next-generation sequencing technology identified genomic alterations in discoidin domain receptor tyrosine kinase 2 (DDR2), cyclin D1 (CCND1), B-cell leukemia/lymphoma 1 (BCL1), colony-stimulating factor 1 receptor (CSF1R), runt related transcription factor 1 (RUNX1) and death domain-associated protein 6 (DAXX6) from the paraffin-embedded tissue. This case will contribute to not only a better understanding of the molecular mechanism of the primary pulmonary NUT carcinomas but also the potential therapeutic option for the patient.

An Overview of Molecular Mechanism, Clinicopathological Factors, and Treatment in NUT Carcinoma

NUT carcinoma (NC) is a rare and poorly differentiated tumor, with highly aggressive and fatal neoplasm. NC is characterized by chromosomal rearrangement involving NUTM1 gene, but lack of specific clinical and histomorphological features. It is more common in midline anatomic sites, such as head and neck, mediastinum, and other midline organs. NC may occur at any age, but mainly in children and young adults. In addition, male and female are equally affected. Most clinicians lack a clear understanding of the disease, and NC diagnostic reagents are still not widely used; therefore, misdiagnosis often occurs in clinic. Due to the highly aggressive nature of the disease and the insensitivity to nonspecific chemotherapy or radiotherapy, many patients have died before the confirmation of NC. In fact, the true incidence of NC is much higher than the current statistics. In recent years, targeted therapy for NC has also made some progress. This article aims to summarize the molecular mechanisms, clinicopathological characteristics, and treatment of NC.

The first report of molecular characterized BRD4-NUT carcinoma in Brazil: a case report

Background

NUT midline carcinoma is a rare and aggressive subset of squamous cell carcinoma, which is characterized by the translocation of nuclear protein in testis gene that is mostly fused with bromodomain and extraterminal family proteins. We describe here the first Brazilian case of NUT midline carcinoma with BRD4-NUT fusion detected in a next-generation sequencing panel and we present the clinical evolution of this patient.

Case presentation

A 42-year-old Caucasian man was diagnosed with poorly differentiated squamous cell carcinoma of the left maxillary sinus, with negative in situ hybridization for Epstein–Barr encoding region and human papillomavirus genotyping. He received induction therapy, chemoradiotherapy with weekly systemic chemotherapy, and, concurrently, weekly intra-arterial chemotherapy. New imaging evaluation, 1 month after the end of the last treatment, revealed a good partial response in the primary lesion. However, positron emission tomography-computed tomography showed multiple suspicious lesions in his bones and lungs, which were histologically confirmed. He died exactly 2 months after metastatic disease was diagnosed.

Conclusions

NUT midline carcinoma is usually very aggressive. Currently, there is no standard of care for treatment of NUT midline carcinoma. The definitive diagnosis must be by demonstration of NUTM1 rearrangement. Immunohistochemical staining of greater than 50% of tumor nuclei on formalin-fixed paraffin-embedded tissue using the monoclonal rabbit antibody to NUT (clone C52B1), has a specificity of 100%, and sensitivity of 87% for the diagnosis of NUT midline carcinoma. Our case is the first Brazilian case of NUT midline carcinoma with BRD4-NUT fusion.

NUTM1 Gene Fusions Characterize a Subset of Undifferentiated Soft Tissue and Visceral Tumors

NUT midline carcinoma is an aggressive tumor that occurs mainly in the head and neck and, less frequently, the mediastinum and lung. Following identification of an index case of a NUTM1 fusion positive undifferentiated soft tissue tumor, we interrogated additional cases of primary undifferentiated soft tissue and visceral tumors for NUTM1 abnormalities. Targeted next-generation sequencing was performed on RNA extracted from formalin-fixed paraffin-embedded tissue, and results validated by fluorescence in situ hybridization using custom bacterial artificial chromosome probes. Six patients were identified: mean age of 42 years (range, 3 to 71 y); equal sex distribution; and, tumors involved the extremity soft tissues (N=2), kidney (N=2), stomach, and brain. On systemic work-up at presentation all patients lacked a distant primary tumor. Morphologically, the tumors were heterogenous, with undifferentiated round-epithelioid-rhabdoid cells arranged in solid sheets, nests, and cords. Mitotic activity was generally brisk. Four cases expressed pancytokeratin, but in only 2 cases was this diffuse. Next-generation sequencing demonstrated the following fusions: BRD4-NUTM1 (3 cases), BRD3-NUTM1, MXD1-NUTM1, and BCORL1-NUTM1. Independent testing by fluorescence in situ hybridization confirmed the presence of NUTM1 and partner gene rearrangement. This study establishes that NUT-associated tumors transgress the midline and account for a subset of primitive neoplasms occurring in soft tissue and viscera. Tumors harboring NUTM1 gene fusions are presumably underrecognized, and the extent to which they account for undifferentiated mesenchymal, neuroendocrine, and/or epithelial neoplasms is unclear. Moreover, the relationship, if any, between NUT-associated tumors in soft tissue and/or viscera, and conventional NUT carcinoma, remains to be elucidated.

A 47-year-old woman with nuclear protein in testis midline carcinoma masquerading as a sinus infection: a case report and review of the literature

BACKGROUND

Nuclear protein in testis midline carcinoma is a rare, highly metastatic undifferentiated carcinoma that typically arises in midline structures and is characterized by having a fusion involving the nuclear protein in testis, NUT, gene. Nuclear protein in testis midline carcinoma has been identified in patients of all ages and is often initially misdiagnosed due to the rapid timeline of symptom onset.

CASE PRESENTATION

Here we report the case of a 47-year-old Caucasian woman with a nuclear protein in testis midline carcinoma that was initially mistaken for a sinus infection. After symptom progression while on an aggressive antibiotic regimen, the source of her symptoms was correctly identified as a sella mass. Comprehensive analysis of the tumor was performed, and standard cytogenetic analysis identified a translocation of 15q and 19p. Further testing identified a NUT-BRD4 fusion and confirmed the diagnosis of nuclear protein in testis midline carcinoma. Despite definitive diagnosis and surgical, radiation, and, ultimately, systemic therapy, she progressed rapidly, developing widespread metastases, and ultimately died from the disease 5 months after diagnosis.

CONCLUSIONS

Based on this and other previous reports, aggressive therapy should be initiated once nuclear protein in testis midline carcinoma is diagnosed and close surveillance employed in an attempt to prevent and/or recognize metastases as early as possible. Aggressive therapy has shown little efficacy such that the average overall survival for patients with nuclear protein in testis midline carcinoma is very short, often less than 6 months. Thus, early enrollment into clinical trials testing novel therapies for the treatment of nuclear protein in testis midline carcinoma should be considered. Finally, additional reports of nuclear protein in testis midline carcinoma are needed to fully characterize this rare and highly aggressive cancer.

Best Practices Recommendations for Diagnostic Immunohistochemistry in Lung Cancer

Since the 2015 WHO classification was introduced into clinical practice, immunohistochemistry (IHC) has figured prominently in lung cancer diagnosis. In addition to distinction of small cell versus non-small cell carcinoma, patients' treatment of choice is directly linked to histologic subtypes of non-small cell carcinoma, which pertains to IHC results, particularly for poorly differentiated tumors. The use of IHC has improved diagnostic accuracy in the classification of lung carcinoma, but the interpretation of IHC results remains challenging in some instances. Also, pathologists must be aware of many interpretation pitfalls, and the use of IHC should be efficient to spare the tissue for molecular testing. The International Association for the Study of Lung Cancer Pathology Committee received questions on practical application and interpretation of IHC in lung cancer diagnosis. After discussions in several International Association for the Study of Lung Cancer Pathology Committee meetings, the issues and caveats were summarized in terms of 11 key questions covering common and important diagnostic situations in a daily clinical practice with some relevant challenging queries. The questions cover topics such as the best IHC markers for distinguishing NSCLC subtypes, differences in thyroid transcription factor 1 clones, and the utility of IHC in diagnosing uncommon subtypes of lung cancer and distinguishing primary from metastatic tumors. This article provides answers and explanations for the key questions about the use of IHC in diagnosis of lung carcinoma, representing viewpoints of experts in thoracic pathology that should assist the community in the appropriate use of IHC in diagnostic pathology.

An overview on the differential diagnostics of tumors of the anterior-superior mediastinum: the pathologist's perspective

The thymus is the main organ in the (anterior) (pre-vascular) mediastinum, playing a central role in the maintenance of both cellular and humoral immunity. The function of the thymus has been long underlooked due to its involution starting during young adulthood and unawareness regarding its immunological function. A variety of primary tumors and inflammatory/reactive/disreactive processes occur in the mediastinum and may involve the anterior-superior compartment and the thymus. Maldevelopment processes also take place in the pre-vascular compartment mediastinum. Although infective diseases do not currently represent the main processes in western countries, they may represent a diagnostic challenge in developing countries. The purpose of this review is to provide a short overview of the main thymic cellular components, their tumors, pseudotumors, in order to provide insights into their clinical setting and the features which assist pathologists in their differential diagnosis (DD). Specific differential diagnostic points are provided, both for "solid" tumors as well as for haematological malignancies, together with a morphological overview of cases of concern that occur in the anterior mediastinum. The main immunohistochemical characteristics of neoplastic/non-neoplastic pathology and updated specific references are also provided.

Nuclear Protein in Testis Carcinoma of the Thorax

Nuclear protein in testis (NUT) carcinoma (NUT-C) is an exceedingly rare and aggressive neoplasm. We herein report a case of a 57-year-old man with a rapidly progressing tumor of the thorax and left pleural effusion. The pathological features and immunohistochemical staining of specimens obtained by a transbronchial lung biopsy initially indicated poorly differentiated squamous cell carcinoma. However, given the clinical presentation along with the additional histopathologic features, NUT-C was considered. Immunohistochemical staining for NUT was positive in the pleural fluid cell block, confirming the diagnosis of NUT-C. This report indicates the utility of immunohistochemical staining for diagnosing NUT in the pleural fluid cell block.