While mutations of the PI3KCA gene are rare in leukemia, events upstream of PI3K are commonly implicated in causing aberrant activation of this pathway, e.g. activating mutations of the receptor tyrosine kinases (RTKs), Fms-like tyrosine kinase 3 (FLT3) and KIT receptor tyrosine kinase, BCR-ABL1 fusion gene, or activating mutations in NRas and KRas [17–20]. The gene discussed is NTRK1; the disease is leukemia.