KMT2A and breast cancer: To determine whether Myb transcriptional elongation in the MLL-AF9 cells is blocked at the SL-dT motif, as reported in ER+ breast cancer and colon cancer, we used intronic RT-qPCR primers corresponding to sequences before and after the SL-dT region (pre-SL and post-SL), as well as exonic RT-qPCR primers representing exons 1, 2 and 9 (refs. 17,30), as depicted in Fig. 3a.