Are Microbial Endophytes the 'Actual' Producers of Bioactive Antitumor Agents?

For millenia, plants have been a major source of medications against human and animal diseases. In the case of anticancer agents, a significant number of current agents can trace their source back to nominally plant secondary metabolites, with examples being taxol, vinca alkaloids, camptothecin (CPT), and their modified derivatives. However, it is now becoming apparent that these and other plant-derived materials, plus similar agents from marine sources may well have a microbe in their background. In this short Opinion, evidence for such claims are presented for some of the agents currently in use or in preclinical and clinical trials against cancer.