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

Cytomorphology of metastatic colonic MXD4::NUTM1-rearranged sarcoma

This report describes the cytologic features of a recently described MXD4::NUTM1-rearranged colonic sarcoma metastatic to the midclavicular soft tissue. Thirteen years ago, a 65-year-old woman presented with a cecal mass and subsequent liver mass. The cecal mass was diagnosed as malignant undifferentiated spindled and epithelioid neoplasm based on morphology and lack of tumor immunoreactivity with a panel of epithelial, smooth muscle, skeletal, melanoma, hematologic, and GIST markers. The liver mass showed morphologic and immunophenotypic similarity to the epithelioid component of the patient's cecal mass, albeit devoid of the spindled component. Fine needle aspiration of the midclavicular soft tissue mass showed singly scattered to clustered epithelioid to rhabdoid tumor cells with centrally to eccentrically located nuclei, prominent nucleoli, and moderate eosinophilic cytoplasm. Immunohistochemical stains performed on the concurrent biopsy showed the tumor cells were positive for NUT and negative for all other additional markers with retained normal expression of SMARCA2 and SMARCA4. Next-generation sequencing showed the presence of MXD4::NUTM1 gene fusion. Due to the identical cytomorphologic findings with the epithelioid component of the patient's prior cecal and liver masses, the tumor was deemed as consistent with a NUTM1-rearranged sarcoma. To our knowledge, this case represents the first reported cytologic features of a NUTM1-rearranged sarcoma on fine needle aspiration. Familiarity with the cytologic features, inclusion of this entity in the differential diagnosis of tumors with epithelioid and/or rhabdoid morphology, and performance of ancillary tests (immunohistochemistry and molecular) will be helpful in arriving at the right diagnosis.

Immunodetection of NUT Protein: Implementation, Indications, and Results in a Tertiary Reference Center

The immunodetection of NUT protein is a reliable tool to identify NUT carcinoma, a rare and still underdiagnosed tumor entity. The technique was implemented in 2017 in our department, a tertiary reference center with a large recruitment in all tumor types, including head and neck and thoracic tumors. We evaluated its use over a 6-year period (2017-2022) to (a) describe the indications for the technique, (b) determine the number of NUT carcinomas detected and confirmed by Fluorescence in situ hybridization, and (c) describe briefly the characteristics of these tumors. Over the study period, 382 NUT immunodetections were performed; the annual number of requests varied from 45 to 83. All 21 pathologists of the department made at least one request (range: 1 to 94; annual mean: 18.2). 54.7% of immunodetections were performed for internal cases, 37% for cases submitted for consultation, and 8.3% for cases submitted for confirmation of a suspected diagnosis. The main indications were poorly differentiated tumors of the head and neck region (39%) and the thorax (19.6%), and difficult-to-classify soft tissue tumors (11.8%). Twelve cases of NUT carcinoma were detected by immunohistochemistry and confirmed by Fluorescence in situ hybridization. Seven were from the head and neck region (4.7% of the tumors tested), 4 from lung or mediastinum (5.3%), 1 from an unknown primary at the time of diagnosis. In conclusion, the implementation of NUT immunodetection in the daily workflow of a pathology department improves the detection of NUT carcinoma. This becomes essential with the emergence of potential targeted therapies.

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.

The expanding universe of NUTM1 fusions in pediatric cancer

NUT midline carcinoma family member 1 (NUTM1) fusions were originally identified in poorly differentiated and clinically aggressive carcinomas typically located in the midline structures of children and young adults, and collectively known as NUT (midline) carcinomas. Next-generation sequencing later uncovered NUTM1 fusions in a variety of other pediatric and adult cancers of diverse location and type, including hematologic malignancies, cutaneous adnexal tumors, and sarcomas. A vast array of NUTM1 fusions with bromodomain containing 4 (BRD4) or bromodomain containing 3 (BRD3), which are characteristic of NUT carcinoma, and with several other fusion partners have been identified and associated with variable prognosis. These non-kinase fusions are thought to cause epigenetic reprogramming, thereby promoting proliferation, and hindering the differentiation of cancer cells. Many questions about both the function of the naïve NUTM1 protein, which is mostly restricted to the germ cells of the testis and is related to spermatogenesis and the oncogenic mechanisms of the various NUTM1 fusions in both adult and pediatric cancer, are still unanswered. Moreover, whether there is a relationship defined by the presence of NUTM1 fusions between conventional NUT carcinoma and other NUTM1-rearranged neoplasms remains to be elucidated. This review will focus on recent discoveries of NUTM1 fusions found in pediatric cancers, their prognostic impact, and emergence as novel oncogenic drivers.

NUTM1-fusion positive malignant neoplasms of the genitourinary tract: A report of six cases highlighting involvement of unusual anatomic locations and histologic heterogeneity

Tumors with NUTM1 fusions occur predominantly in the thoracic cavity and head and neck region. However, recent literature expanded the location of NUTM1-translocated malignancy to soft tissue, brain, and visceral organs. In this study, we describe the first series of six NUTM1-translocated carcinomas and sarcomas occurring in the genitourinary tract. The sites of origin were kidney (n = 2), bladder (n = 3), and penis (n = 1). All tumors occurred in adulthood (range: 30-78 years). The histologic features were heterogeneous, showing epithelial, spindle cell, or primitive small blue round cell morphology. Glandular architecture, keratinization, rhabdoid cells, or myxoid-to-edematous stromal component were also noted. In three cases, features were in keeping with a carcinoma (two from kidney and one from bladder), whereas the remaining three were classified as malignant undifferentiated neoplasm (MUN)/sarcoma. Fusion partners detected in four cases tested by either FISH and/or RNA sequencing were BRD4 in two kidney tumors, MXD1 in a bladder sarcoma, and MXD4 in a penile sarcoma. NUT immunostain showed diffuse spiculated positivity in five cases. Immunopositivity for various cytokeratins was noted in two tumors. The outcome of NUTM1-rearranged genitourinary malignancy was dismal: four of five cases with follow-up developed distant metastasis, and three suffered disease-specific death. In conclusion, NUTM1-rearranged carcinoma and sarcoma can affect the genitourinary tract, including kidney, bladder, and penis. Histologic features and keratin immunoexpression are highly variable. A NUTM1-fusion positive malignancy may be included in the differential diagnosis of a MUN of the genitourinary tract given the dismal outcome and the existing BET-targeted therapy for tumors with BRD3/4::NUTM1 fusion.

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.

Cytomorphology of NUTM1-rearranged sarcoma involving pleural fluid

We describe an exceedingly rare cytology case of a NUTM1-rearranged sarcoma involving pleural fluid. A 48-year-old female presented with progressive abdominal pain. Computed tomography (CT) scan of the abdomen revealed a 5.6 cm soft tissue mass in the right hemi-abdomen. Needle core biopsy of the mass showed a small round cell tumor. Extensive work-up including next generation sequencing (NGS) demonstrated a NUTM1:MXI1 rearranged sarcoma. The patient was first treated with ifosfamide, carboplatin, and etoposide (ICE) chemotherapy. She responded initially and then progressed with multiple masses in the abdomen and pleural effusion. The cytology of the pleural effusion showed clusters and single small round blue cells. Some of them displayed rhabdoid morphology. Immunostains of NUT antibody on cell block demonstrated strong positivity of NUT. NUTM1-rearranged sarcoma is an emerging class of mesenchymal neoplasm and the cytomorphology of this neoplasm in liquid-based cytology (LBC) is yet to be described. We herein reported the first cytology case of NUTM1-rearranged sarcoma in pleural fluid.