Tesmilifene is a small-molecule antineoplastic drug and chemopotentiator that was under development by YM BioSciences for the treatment of breast cancer. Tesmilifene was developed as a selective ligand of the antiestrogen binding sites without estrogen receptor affinity. Tesmilifene potentiates the cytotoxicity of a variety of chemotherapy drugs in vitro and in vivo. Tesmilifene in combination with doxorubicin provides an unexpected and very large survival advantage over doxorubicin alone in a randomized trial in phase III clinical trial in advanced breast cancer. Unfortunately, Tesmilifene application associated with high rate disease and treatment-related adverse events and poor quality of life. Based on these results further development of Tesmilifene was discontinued