H3K79me2/3, a histone modification found at high levels at MLL-FP gene targets [16, 17], was observed to colocalize with MLL-AF4 at PROM1 in SEM, RS4;11, and the MLL-AF4 ALL primograft cells, further validating the gene as a bona fide MLL-AF4 target (Fig. 2b). The gene discussed is AFF1; the disease is acute lymphoblastic leukemia.