Besides secondary resistance mutations in KIT or PDGFRA, concomitant mutations in other signaling proteins, such as EGFR, PI3K, RAS, PTEN, NF1, TSC2, SDH, PP2A, FGFR1, FGFR3, and FGF4 have been reported in GIST patients and are associated with poor prognosis [37]. Here, PIK3CA is linked to gastrointestinal stromal tumor.