FGF2 and breast cancer: After screening a library of recombinant secreted microenvironmental proteins, fibroblast growth factor 2 (FGF2) was discovered to be an essential regulator of anti-estrogen resistance, mechanistic target of rapamycin complex 1 (mTORC1) inhibition, and phosphatidylinositol 3-kinase inhibition in ER+ BC [158].