Tesetaxel is a taxane derivative patented by Daiichi Pharmaceutical Co., Ltd. as antitumor agent. Preclinical research suggests that tesetaxel may overcome P-glycoprotein-mediated multidrug resistance, thereby facilitating extended intracellular retention and possibly clinical effectiveness. Tesetaxel exhibited potent cytotoxicity against various human and murine cancer cell lines and was particularly potent against cell lines expressing P-glycoprotein. Orally administered tesetaxel showed potent in vivo antitumor activity in murine syngeneic and human xenograft models. The cytotoxic effect of tesetaxel, unlike that of other taxanes, was not influenced by the level of P-glycoprotein expression or by the presence of a P-glycoprotein modulator. In patients with metastatic breast cancer, tesetaxel was shown to have significant, single-agent antitumor activity in two multicenter, Phase 2 studies.