NUT carcinoma t(15;19)
46,XY,t(15;19)(q14;p13.1)
Also known as: BRD4-NUTM1, NUT midline carcinoma, t(15;19)
46,XY,t(15;19)(q14;p13.1) is the translocation of NUT carcinoma, fusing BRD4 with NUTM1. It defines an aggressive midline carcinoma of children and young adults, and it is one of the few carcinomas simple enough for the karyotype itself to be diagnostic.
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What the notation means
46 is the number of chromosomes counted in the cell. That is the normal number: 22 pairs of autosomes, the chromosomes other than X and Y, plus one pair of sex chromosomes. XY lists the sex chromosomes, here one X and one Y, the usual male set. These two fields open every karyotype because they describe the whole cell. Any abnormality is written after them.
A TRANSLOCATION (t): two chromosomes exchange segments. (15;19) lists the two chromosomes that exchanged segments, 15 and 19. The lower number is written first, or the sex chromosome if one is involved, so that the same translocation is always written the same way. (q14;p13.1) gives one breakpoint on each chromosome, in the same order as the chromosomes, so the breakpoints are 15q14 on 15 and 19p13.1 on 19. Each chromosome keeps its own centromere and takes the segment beyond the other's break.
Clinical notes
t(15;19), NUT carcinoma
BRD4::NUTM1. This translocation means NUT carcinoma, an aggressive midline carcinoma of children and young adults with median survival under a year. Almost no other carcinoma is defined by a single rearrangement: solid tumours usually carry complex genomes, and this one was diagnosable from its karyotype before its gene was known. NUT immunohistochemistry is the practical test, and the BRD4 partner made the disease the proving ground for BET inhibitors.