For instance, 5-fluorouracil (5-FU), a major anti-tumor drug used for treating various tumors including colon carcinoma, esophageal squamous cell carcinoma, and breast cancer, induces the activation of the IRE1α/XBP1 pathway, leading to the upregulation of ATP binding cassette (ABC) transporters, which are crucial for drug resistance [131]. This evidence concerns the gene XBP1 and breast cancer.