WEE1 inhibitor AZD1775 disrupts endoplasmic reticulum proteostasis and activates the protein kinase RNA‐like ER kinase and inositol‐required enzyme 1α (IRE1α) arms of the unfolded protein response in ovarian cancer cells with mutant p53, which is mediated by NF‐κB‐induced senescence‐associated secretory phenotype. Here, TP53 is linked to ovarian cancer.