FGFR1 and acute myeloid leukemia: Furthermore, bone marrow microenvironment-mediated resistance has been reported, involving upregulation of FLT3 ligand and fibroblast growth factor 2 (FGF2) by mesenchymal stromal cells, which activate AML cells via wild-type FLT3 and fibroblast growth factor receptor 1 (FGFR1) [21].