According to the WHO, brachyury is considered the diagnostic hallmark of a chordoma [14] because of its frequent occurrence (up to 79/80 chordoma cases, according to Miettinen et al., 2015 [15]) and high specificity in distinguishing a chordoma from morphological mimics such as a chondrosarcoma and mucinous adenocarcinoma [13]. The gene discussed is TBX1; the disease is chordoma.