FGFR1 and gastrointestinal stromal tumor: Importantly, despite the high levels of expression of FGFR1, 2 and VEGFR1 observed in IM-resistant GIST 430 cells, the aforementioned RTKs were not co-localized and co-immunoprecipitated as well (Figure 4B,D, respectively), thereby suggesting that the overproduction of FGF2 and VEGF-A ligands in IM-resistant GISTs plays an important role in the complex formation between FGFRs and VEGFRs.