XBP1 and breast cancer: Previous studies reported that in breast cancer, lung cancer, oral squamous cell carcinoma, and hepatocellular carcinoma, XBP1-s promotes metastasis by directly upregulating the transcription of EMT-inducing factors, such as Snail and zinc finger E-box (ZEB), leading to poor prognosis and a low survival rate [42,111,112,125,126].