CDK4 and breast cancer: Fibroblast growth factor receptor (FGFR) signaling pathway is activated in a variety of tumor types including BC.[43,44] Among the five FGFRs, FGFR1-4 has been confirmed that they cancer progression, CDK4/6 resistance, and endocrine resistance.[45] Studies have shown that FGFR1 amplification activates PI3K/Akt and Ras/MEK/ERK signaling pathways in endocrine resistant BC cells.[46] The FGFR pathway is activated primarily by FGFR2 amplification, which allows FGFR1 to mediate endocrine resistance.