ERN1 and breast cancer: Mechanistically, H2S‐mediated S‐sulfhydration of the protein chaperone glucose‐regulated‐protein 78 (GRP78) induced endoplasmic reticulum transmembrane protein kinase‐1α (IRE‐1α) dissociation from GRP78, which enhanced the phosphatase activity of IRE‐1α itself in BC‐TAMs, while the Cys420 site mutation of GRP78 interfered with these effects.