Evidence of the lack of inhibition of the activated PI3K pathway by imatinib and the deficiency of PTEN expression due to PTEN (p.T321fs) mutation collectively in GIST-RX1 led us to investigate further the antitumor effects of the PI3K inhibitor LY294002 alone or in combination with imatinib in this model (Supplementary Figure 2). Here, PTEN is linked to gastrointestinal stromal tumor.