CD44 and breast carcinoma: FK506-binding protein like (FKBPL), a novel member of the immunophilin protein family,8,9 is a potent secreted antiangiogenic protein10,11 targeting the CD44 pathway.12 FKBPL is also a prognostic biomarker for breast cancer and predictive for endocrine therapy.13,14 Therapeutic peptide derivatives of FKBPL, AD-01 and ALM201, have highly potent antiangiogenic activity, and because of their CD44-mediated effect, these agents are also able to target CD44-positive cancer stem cells,15 further strengthening their therapeutic potential.