RUNX1 and acute myeloid leukemia: An RUNX1 frameshift mutation in exon 4 (c.497_498insGA) with a variant allele frequency (VAF) of 31.1% could be detected in the mediastinal EM from initial diagnosis (Figure 3(a)), however, suggesting the existence of two molecularly and anatomically distinct AML clones at time of diagnosis as the RUNX1 mutation was not detected in the BM.