Both XBP1-u and XBP1-s are highly expressed and can drive the development of a variety of tumors, including colorectal cancer, hepatocellular carcinoma, multiple myeloma, ovarian cancer, breast cancer, melanoma, and bladder cancer, by regulating various aspects of tumorigenesis (Table 2) [34,100,101,102,103,104,105]. The gene discussed is XBP1; the disease is breast cancer.