FKBPL and breast cancer: FK506-binding protein-like (FKBPL) and AD-01 (one of the its derivatives) are novel biological agents that have an effective role in inhibiting tumor growth initiation, angiogenesis, and metastasis of BC cells as well as BCSCs through targeting CD44 pathway and downregulating DLL4, a Notch ligand, and Notch4 (118, 119).