A functional study has demonstrated that XBP1 promotes cell growth and XBP1‐mediated cancer cell proliferation by upregulating matrix metalloproteinase‐9.35 Some studies have shown that XBP1s overexpression prevents cell cycle arrest in breast cancer cell lines and that XBP1 may participate in cell cycle regulation.36 Indeed, XBP1 is an important regulator of cell cycle and proliferation. This evidence concerns the gene XBP1 and breast cancer.