CREBBP and acute lymphoblastic leukemia: The identification of subclonal KRAS codon 12 and 13 mutations in our initial analyses led us to investigate microclonal mutations (MAF < 10%) at ALL hotspot loci in KRAS, NRAS, FLT3, PTPN11, and CREBBP. Utilizing the high-coverage sequencing data we revealed an extraordinary level of intra- and inter-tumoral heterogeneity, with microclonal Ras pathway hotspot mutations detected in over 50% of patients.