An estradiol‐cisplatin hybrid conjugate showed antiproliferative activity in the low micromolar range, which was more potent than cisplatin alone in estrogen‐dependent and estrogen‐independent breast cancer cell lines MCF‐7 and MDA‐MB‐231, respectively.111 Additionally, this conjugate displayed high affinity toward the estrogen receptor α and was superior to cisplatin in inducing tumor regression in the MCF‐7 human breast cancer tumors in a mouse model. This evidence concerns the gene ESR1 and breast cancer.