KAI1/CD82 is a tumor metastasis suppressor in various cancers without affecting tumor formation [27]; it is significantly downregulated in estrogen receptor (ER)‐positive breast cancer, and the ER antagonist fulvestrant was able to reverse ER‐mediated gene repression, induce significant KAI1/CD82 upregulation, and inhibit breast cancer cell proliferation and migration [28]. Here, ESR1 is linked to breast cancer.