PIK3CA and precursor B-cell acute lymphoblastic leukemia: Moreover, although KMT2A (MLL1)-r has one of the lowest frequencies of somatic mutations in childhood B-ALL, mutations in kinase-PI3K-RAS signaling pathway components (FLT3, KRAS, NRAS, NF1, PTPN11, PIK3CA, and PIK3R1) have been described in 47% of these cases [45].