Paclitaxel and docetaxel are the two presently clinically available representatives of the new class of taxane drugs. They share major parts of their structures and mechanisms of action, but differ in several other aspects. For instance, there is a difference in their tubulin polymer generation, and docetaxel appears twice as active in depolymerization inhibition. In vitro docetaxel also tends to be more potent in different cell lines and investigational models. For more than 30 years, the chemotherapy drugs paclitaxel and docetaxel have been frontline therapies in the treatment of many forms of cancer - and two of the most successful naturally-derived compounds ever to become medicines. Paclitaxel, sold mainly under the brand name Taxol, was first isolated in 1971 from endophytic fungi in the bark of the Pacific yew tree Taxus brevifolia. It is a chemotherapeutic used mainly as a treatment for breast, lung, ovarian and pancreatic cancers, and works as a mitotic inhibitor - blocking cell growth by stopping mitosis, or cell division.