NUT midline carcinoma (NMC), also known as t(15; 19) carcinoma, is a form of rare, aggressive, poorly differentiated cancer that is defined by the presence of a gene rearrangement in the NUT gene, which encodes a nuclear protein normally expressed in the testes. To date, under 1000 total NMC cases have been reported, with the first report coming from Kubonishi et al. in 1991 [
Approximately 70% of NMC cases present with a translocation of the BRD4 gene, resulting in a roughly 6.4 kb BRD4-NUT fusion gene. In the remaining 30% of NMC cases, NUT fuses with BRD3 or other unknown genes [
In many instances, NMC can be misdiagnosed as another form of poorly differentiated tumor. The only definitive way to diagnose NMC is through the detection of NUT gene translocation via either immunohistochemistry, fluorescence in situ hybridization (FISH), or gene sequencing.
Herein, we report on 5 cases of NMC who presented to our institution, including one case arising in the maxillary gingiva, which has never been described previously. We summarize both the clinical and pathological features of NMC and discuss the differential diagnosis for these tumors in order to better understand this rare and aggressive disease.
This study was approved by the Institutional Review Board of the Department of Pathology, Ruijin Hospital, Shanghai Jiaotong University School of Medicine. In total, 5 cases of NMC were retrospectively analyzed as a part of this study. For each of these cases, complete clinical data were reviewed, and all available hematoxylin and eosin- (H&E-) stained slides were analyzed independently by two experienced pathologists (LT. Z. and X. Y.). In addition, patient follow-up was conducted via telephone interview.
Available tissue sections were used for immunohistochemistry (IHC) analyses of these 5 NMC cases. Surgical tissue sections were sectioned at 4
Translocations of the NUTM1 gene at 15q14 were analyzed via FISH using the ZytoLight SPEC NUTM1 Dual Color Break Apart Probe. Samples were first fixed for 24 h with 10% neutrally buffered formalin at room temperature, embedded at a temperature below 65°C, and sliced into 2–4
Key clinical findings for patients in this study are compiled in Table
Clinicopathological characteristics of NUT carcinomas.
Case | Gender | Age (years) | Location | Size (cm) | Treatment | Died of disease |
---|---|---|---|---|---|---|
1 | Female | 59 | Orbit | 1 × 1 × 1 | Without treatment | 4 months |
2 | Female | 35 | Larynx | 3 × 2 × 1 | Cisplatin chemotherapy | 9 months |
3 | Female | 38 | Gingiva | 2 × 1.5 × 1 | Surgical resection | AWD |
4 | Male | 26 | Lung | 2 × 2 × 2 | Etoposide chemotherapy | 5 months |
5 | Male | 69 | Lung | 5 × 4.8 | Etoposide chemotherapy | 6 months |
AWD: alive with diseases.
NUT carcinoma imaging characteristics. MRI scans revealing a 1 cm mass infiltrating the right orbit (a). CT scans revealing the presence of a 2 cm × 1.5 cm ovoid shadow at the apex of teeth 11-12 surrounded by dense white lines and an unclear boundary (b). CT scans indicating the presence of an area of soft tissue of irregular density within the right lung hilum, with contrast-enhanced images revealing the presence of nonhomogeneous enhancement and local necrosis (c).
The remaining 2 cases of NMC in the present study were found in the lungs of affected patients. Case 4 was a 26-year-old male who presented with fever, shortness of breath, and a dry cough that had been present for 5 days. The symptoms of this patient had been progressing rapidly, and he exhibited pronounced shortness of breath and difficulty lying on his back. A tube endoscopy of this patient revealed the presence of enlarged protuberances, nodular hyperplasia, and mucosal protuberance at the anterior wall of the lower trachea, together with obstruction of the right middle bronchial lumen. CT scans revealed atelectasis of the middle and lower lobes of the right lung, with dense patchy shadows that were evenly enhanced following enhancement, together with mediastinal and right lower hilar lymphadenopathy. Case 5 was a 69-year-old male that had presented with chest tightness and asthma over the preceding 10 days. CT scans revealed the presence of soft tissue masses with poorly defined margins in the right hilum of the lung (Figure
For these cases, hemorrhage and necrosis were frequently detected within tumors. From a morphological perspective, these tumors were composed of poorly differentiated cells arranged in clusters that were separated by fibrous stroma. These tumors commonly exhibited poor adhesion and large areas of coagulative necrosis. Cells had relatively substantial nuclear and cytoplasmic contents, with uniform nuclei, numerous mitotic figures, and evident nucleoli. All 5 cases exhibited interstitial neutrophil infiltration. Keratosis was evident in cases 1 and 2, but not in case 3, while in cases 4 and 5, it was present in the gingiva and lung (Figure
NUT carcinoma histological features. NUT carcinomas of the gingiva exhibit fragmented tissue and tumor cell clusters, with locally visible bone fragments present within the gingiva (10x) (a). Poorly differentiated tumor cells with large nuclei are evident in dense clusters separated by fibrous stroma in another region of the gingival NMC tumor (40x) (b). Abrupt regions of focal keratinization are evident in the case of orbital NMC (100x) (c). Focal necrosis is evident in the case of laryngeal NMC (d). Neutrophil infiltration is prominent in the case or laryngeal NMC (200x) (e). Focal squamous differentiation is evident in the case of orbital NMC (100x) (f).
IHC staining of these tumor samples confirmed all cells to be positive for NUT (Figures
NUT carcinoma immunohistochemical and molecular features. Diffuse nuclear NUT IHC staining for the case of gingival NUT carcinoma (100x) (a), laryngeal NUT carcinoma (100x) (b), orbital NUT carcinoma (100x) (c), and lung NUT carcinoma (100x) (d). Diffuse nuclear EGFR IHC staining for the case of lung NUT carcinoma (100x) (e). NUT break-apart probe FISH revealed the presence of distinct red and green signals consistent with NUT gene translocations in all 5 cases (1000x) (f).
FISH was conducted using a NUT-specific probe to identify NUT gene locus rearrangements with an appropriate probe such that distinct red and green signals corresponded to translocations within this region. All 5 NMC cases in the present study presented with dual color FISH probe staining consistent with the translocation of the NUT gene locus (Figure
NMC has a poor prognosis. As reflected in Table
NMC is a form of rare, aggressive, and poorly differentiated disease that can affect many organs but that most often originates in the midline regions of the head and neck, lung, and mediastinum, although it has also been reported in other tissues including the kidney, bladder, liver, salivary glands, and pancreas [
The exact etiology of NMC remains to be fully clarified. Previous studies have found it to be unrelated to Epstein–Barr virus or hepatitis B virus infections. NMC patients have also not been found to exhibit a history of smoking. Somatic gene rearrangements of the NUT gene locus appear to be the basis for the development of NMC, with a single clonal translocation of the MUT (NUTM1) gene in the q14 region of chromosome 15 being evident in 100% of NMC cases. In roughly 70% of these cases, the NUTM1 gene exhibits a reciprocal translocation with BRD4 on chromosome 19p13.1 [
Based on morphological findings alone, NMC diagnosis can be extremely challenging as microscopic findings are largely nonspecific and can range from a completely undifferentiated carcinoma to a carcinoma with squamous differentiation and abrupt keratinization that may be either focal or prominent. NMC tumor cells are often epithelioid in appearance, with a rounded or ovoid nucleus, clearly visible nucleoli, high rates of mitosis, and clear evidence of necrosis and neutrophil infiltration. NUT expression was evident in all tumors upon IHC staining, with speckled nuclear positivity in >50% of tumor cells using a highly specific monoclonal nuclear NUT antibody [
In the present study, strong NUT staining was evident in all 5 cases, whereas all 5 were negative for CD34, chromogranin, and synaptophysin, and only 1 was positive for EGFR. NUT translocation was detectable by FSH in all cases. A combination of IHC and FISH analysis allows for NUT diagnosis with sensitivity and specificity values approaching 100%.
NMC has an extensive differential diagnosis including squamous cell carcinoma, small-cell carcinoma, basal cell carcinoma, Ewing sarcoma, metastatic germ cell tumor, mucosal melanoma, lymphoma, and rhabdomyosarcoma. NUT carcinoma is frequently misdiagnosed as poorly differentiated squamous cell carcinoma, as NMC tumors often exhibit local squamous differentiation and squamous cell carcinoma marker expression. However, squamous cell carcinoma is NUT-negative upon IHC analysis. NMC has a significantly poorer prognosis than does squamous cell carcinoma, making accurate diagnosis essential in order to accurately predict patient outcomes.
It is important that NMC be differentiated from small-cell carcinomas. Small-cell carcinomas exhibit a histological morphology similar to that of midline carcinomas, but without abrupt focal keratinization. These tumors also typically stain positive for neuroendocrine markers, CD56, and TTF-1, whereas they stain negative for NUT. Basal cell carcinomas may exhibit squamous epithelial differentiation and focal keratinization, but these tumors most often arise in superficial areas closely associated with the epidermis. Cells surrounding these tumor clusters are typically arranged in a palisade formation, with clear melanin deposition within tumor cells. Ewing sarcoma tumors do not exhibit squamous differentiation, with diffuse positive CD99 IHC staining and negative CK and NUT staining. FISH can confirm the presence of an EWS-FLI-1 fusion gene in these tumors.
NMC is a very aggressive disease, with patients having a median survival of only 7 months [
In summary, NMC is a form of rare yet highly aggressive and invasive cancer. Morphological features of NMC include focal keratinization and poorly differentiated clusters of tumor cells. In addition to better-documented sites, NMC tumors can arise in the orbit and the gingiva. NUT gene rearrangement was evident in all NMC cases, as detected by FISH. As additional cases of NMC continue to be identified and studied, further insight into the cellular and molecular origins of these tumors will be gained, thereby helping to identify viable therapeutic strategies and to improve patient prognosis.
The data used to support the findings of this study are available from the corresponding author upon request.
The authors declare that there are no conflicts of interest regarding the publication of this paper.
Luting Zhou and Xiang Yong contributed equally to this work.
This work was supported by the Shanghai Science and Technology Commission (17ZR1417500).