Demystified molecular pathology of NUT midline carcinomas.

NUT midline carcinoma (NMC) is a rare, highly lethal cancer that occurs in children and adults of all ages. NMCs uniformly present in the midline, most commonly in the head, neck or mediastinum, as poorly differentiated carcinomas with variable degrees of squamous differentiation. This tumour is defined by rearrangement of the nuclear protein in testis (NUT) gene on chromosome 15q14. In most cases, NUT is involved in a balanced translocation with the BRD4 gene on chromosome 19p13.1, an event that creates a BRD4-NUT fusion gene. Variant rearrangements, some involving the BRD3 gene, occur in the remaining cases. NMC is diagnosed by detection of NUT rearrangement by fluorescence in situ hybridisation or reverse transcriptase PCR. Due its rarity and lack of characteristic histological features, most cases of NMC currently go unrecognised.