TAT-PiET -PROTAC is a proteolysis-targeting chimera ( PROTAC )-modified TAT-PiET. TAT-PiET is a cell-penetrating peptide targeting the extra-terminal (ET) domain of BRD4. TAT-PiET -PROTAC can disrupt the interaction between the breast cancer oncogene BRD4/JMJD6 and inhibit the growth of breast cancer cells. TAT-PiET -PROTAC also resists the endocrine resistance of ERα-positive breast cancer cells and is a potential inhibitor of breast cancer. TAT-PiET -PROTAC can be used for the synthesis/research of Radionuclide-Drug Conjugates (RDCs).