FGFR1 and breast cancer: Analysis of FGF ligand expression in MDA-MB-231 cells revealed increased expression of ligands known to bind FGFR1, including FGF1, FGF19, FGF21 and FGF23 [24], suggesting that breast cancer cells express multiple potential regulators of FGFR1 activation that may act redundantly to induce FGFR signaling in osteoclasts.