An enrichment in mutations in genes coding for transcription factors (TFs), such as GATA3, CTCF, FOXA1, and MYC (31); and chromatin modifiers, such as the histone methyltransferases (KMT2B, KMT2D, KMT2E) and histone demethylases (KDM4A, KDM5B, KDM5C, KDM6A) (20), and SWI/SNF complex subunits (ARID1A, ARID2) (31), have also been observed in ER+ breast cancer. The gene discussed is PRDM9; the disease is breast cancer.