RUNX1 and leukemia: However, the potency of the leukemic phenotypes observed needs to be placed in the context of the low penetrance of ETV6-RUNX1 as an oncogene; thus, of the 1% of children born harboring this mutation only 1% progress to leukemia, and those with the pre-leukemia have no discernible phenotype and only modest pre-leukemic clonal size (Mori et al., 2002).