Botanical medicines for the treatment of cancer: rationale, overview of current data, and methodological considerations for phase I and II trials.

There appears to be exceptional and growing public enthusiasm for botanical, or "herbal", medicines, especially amongst cancer patients. This has recently begun to be matched by increasing scientific attention. Whilst it is known that plant extracts are active against cancer, the standard approach has been to isolate, synthesize and administer the single chemical compound thought responsible for this effect. However, different components in a botanical may have synergistic activities. There is also some evidence that the presence of multiple compounds in a botanical extract can buffer the toxic effects of a single constituent. Though many of the botanicals popular among patients are probably not of benefit (e.g. Mistletoe, Pau D'arco), several botanicals have shown promise in Phase III (Sho-saiko-to, PSK) or Phase II (PC-SPES) trial. Quality control of botanicals poses significant challenges: small differences in genetics, soil, temperature, moisture and time of harvesting can lead to significant differences in the concentration of important constituents. Phase I and II methodology is also problematic: botanicals have low toxicity and are unlikely to cause rapid tumor regression. There is currently minimal regulation of botanical medicines.