KMT2A and acute lymphoblastic leukemia: Interestingly, there was a large difference between the levels of total cfDNA measured from the MLL-1 cohort (maximum 600 pg/μL) and MLL-2 (maximum 7000 pg/μL) and MLL-7 (maximum 6000 pg/μL), indicating variability between PDXs of the same ALL subtype (Figure 2A).