SET and chordoma: Poorly differentiated chordomas (PDCs) are a recently recognized distinct subgroup of chordoma, which occurs predominantly in children, and is characterized by the expression of brachyury, an embryonic transcription factor encoded by the TBXT gene, and by loss of the SWI/SNF chromatin remodelling factor subunit, INI1, encoded by the SMARCB1 gene1–5.