AGR3, a member of the protein disulfide isomerase (PDI) family, has been implicated in various biological processes and disease conditions. It has been found to be associated with pathways such as Wnt/β -catenin signalling [3]. In cancer research, understanding AGR3's function is crucial due to its potential role in carcinogenesis [2].

In breast cancer, AGR3 expression is associated with histological grade II, estrogen and progesterone receptor positivity, low ki67 expression, recurrence or distant metastasis, and lumen subtypes. In patients with low and intermediate histological grades, AGR3 expression is related to worse overall and disease-free survival, suggesting it could be a biomarker for early detection and prognosis prediction in luminal subtypes [1]. AGR3 promotes estrogen-receptor positive breast cancer cell proliferation in an estrogen-dependent manner, and also promotes tamoxifen resistance by activating the estrogen receptor signalling pathway [5,7]. It may also serve as a microenvironmental signalling molecule regulating breast cancer cell migration via Src signalling [6].

In colorectal cancer, AGR3 promotes the stemness of cancer cells by activating the Wnt/β -catenin signalling pathway, which is important for cancer initiation and progression [3].

In patients with frequent exacerbations of COPD, AGR3 expression in lung tissue is decreased, and it may play a role in maintaining airway epithelial junctions, as its loss might increase susceptibility to COPD exacerbations [4].

In conclusion, AGR3 plays significant roles in cancer progression, especially in breast and colorectal cancers, and in the susceptibility to COPD exacerbations. Its functions in promoting cell proliferation, stemness, and metastasis in cancer, and maintaining epithelial integrity in the context of COPD, highlight its importance as a potential biomarker and therapeutic target. The studies on AGR3 contribute to a better understanding of the underlying mechanisms of these diseases.