Many chemotherapeutic drugs are derivatives, usually synthetic, of plants.
For example, vincristine and vinblastine are derivative of the Madagascar periwinkle whose vinca alkaloids have significant anticancer actions. There are more varieties of cytotoxic herbs than there are chemotherapeutic drugs. Hartwell researched all references to cancer herbs spanning 5000 years and 2,500,000 herbs. Of these, at least 3000 possess some anti-cancer activity. This is the same figure used by the U.S. Department of Agriculture.