We investigated the role of the transcriptional mediator subunit 23 (MED23) in everolimus drug resistance, invasion and metastasis during breast cancer treatment and its molecular mechanism. We also evaluated the endocrinotherapy and prevention method for breast cancer. Breast cancer cell strains were established that can continuously express MED23, as well as inducible MED23-shRNA expression plasmids. The inductive agent, doxycycline (Dox), was added to the water for long‑term silencing of MED23 in intratumoral cells. We conducted experiments on the role of MED23 in the regulation of invasion and metastasis of breast cancer using cell culture, western blotting, MTT proliferation experiment, fluorescent quantitative PCR and chromatin immunoprecipitation (ChIP). The silencing of MED23 significantly inhibited cellular growth and proliferation as well as soft agar cloning. Silencing of MED23 strengthened the sensitivity of the everolimus-resistant breast cancer cell strains BT474 and MCF‑7/ADM cells to everolimus medication. The silencing of MED23, in combination with everolimus, inhibits the cell cycle progress of breast cancer cells. ChIP indicated that the mutual regulation of HER2 and MED23 also participates in the formation of the everolimus drug resistance mechanism. Therefore, MED23 plays an important role in everolimus drug resistance, invasion, and metastasis of breast cancer. As a potential molecular therapeutic target of breast cancer, MED23 overcomes drug resistance in clinical endocrinotherapy and controls the distal relapse and metastasis in breast cancer by the targeted silencing of MED23.

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