However, contrary to these events, FGF-2 inhibits proliferation of ER+ breast cancer cells by activation of cell cycle inhibitors p21WAF1/Cip1, p27KIP1 and p15INK4B resulting in dephosphorylation and activation of retinoblastoma protein (Rb) and cell cycle arrest [35, 48]. This evidence concerns the gene ESR1 and breast cancer.