Organometallic chemistry has allowed the design and emergence of a new class of metal-based bioactive molecules and a variety of drugs used or still tested against cancer. In this field, beyond the well-known cisplatin, major contributions have focused on the functionalization of clinically validated purely organic drugs with complexes derivatized by a metallocene group. This approach, which exalts the anti-cancer properties of the organic moiety, has been successfully used to design ferrocifens. These complexes involve a ferrocenyl group covalently grafted onto the tamoxifen skeleton, the current gold standard for endocrine breast cancer therapy. Based on the same strategy, several original ruthenocene (Rc)-tamoxifen derivatives and osmocene (Os)-tamoxifen derivatives have been recently synthesized and successfully tested against breast and other cancer cells. The development of such potent metallodrugs was made possible thanks to the accurate mechanistic understanding of the metallodrugs activation provided by the synergistic combination of electrochemical and biological approaches.