FGFR1 is a receptor tyrosine kinase activated upon binding of the FGF ligand, which activates RAS-MAPK and PI3K-AKT pathways. Altered function of FGFR1 in cancer may lead to increased cell proliferation and decreased apoptosis. Simple variants in FGFR1 are seen in about 1% of all tumors, including about 2% of colorectal cancers and skin tumors. Preclinical studies have shown that breast and lung tumors with FGFR1 variants respond to FGFR1 inhibitors.