PIK3R1 and acute lymphoblastic leukemia: Of the 33 cancer-associated mutations that were present in more than 2% of cells, 31 targeted PI3K/RAS genes, a category of genes that is often mutated in KMT2A-r infant ALL.5,27 The mutations included KRAS (n = 14, 8 cases), NRAS (n = 10, 9 cases), FLT3 (n = 5, 5 cases), PIK3CA (n = 1) and PIK3R1 (n = 1) (Figure 2B; Suppl.