Control experiments verified the induction of KIT phosphorylation on Y721, the docking site for the p85 subunit of PI3K [1], by exogenous KITLG in GIST-T1 cells containing a heterozygous activating KIT mutation (Figure 1A; see reagent concentrations, exposure times, replicate numbers and other statistical details in the figures and their legends). This evidence concerns the gene KIT and gastrointestinal stromal tumor.