– Anterior gradient protein (AGR) 3 is a highly related homologue of pro-oncogenic AGR2 and belongs to the family of protein disulfide isomerases. AGR3 was found in breast, ovary, prostate, and liver cancer, it is associated with the level of differentiation, slowly proliferating tumors, and more favorable prognosis of breast cancer patients. AGR3 is a specialized member of the PDI family that plays an unexpected role in the regulation of CBF and mucociliary clearance in the airway. AGR3 had been characterised as a novel potential biomarker both for breast cancer prognosis and early breast cancer detection from blood.