Risk Management of Complementary Alternative Medicines in Cancer

Purpose: Cancer patients widely use complementary alternative medicines. Although some remedies have been shown to be of benefit, there is also a risk of potentially serious interactions with conventional cancer therapies and diagnostic procedures. The aim of this review is to identify the main factors which might make complementary medicines potentially unsafe in cancer.

Method: Systematic review of potential interactions with chemo- and radiotherapy and review of the purported mechanisms of action.

Results: Four factors were identified. These included the potential modification of the clinical course, interaction with the pharmacodynamics and pharma-cokinetics of conventional therapies and potential alterations of investigations. Complementary immunostimulants may be contraindicated in lymphomas and other cancers in which suppression of the immune system is desired. Phytoestrogens could stimulate growth of hormone sensitive cancer cells. Antioxidants should not be used in chemotherapies whose mechanisms of action rely on cell damage through oxidative stress. Many remedies can interact with the cytochrome P450 system thereby potentially changing plasma levels of conventional medicines. However, in vitro effects or findings from animal studies may not translate into clinically relevant effects. Some remedies may interfere with the membrane transporter proteins thereby contributing to multi-drug resistance. Finally some complementary medicines remedies may interfere with unsealed source radiotherapy or nuclear scans.

Conclusions: Predicting the safety profile of complementary medicines is complex and may depend on personal and genetic factors. In cancer therapy, where the therapeutic margin of chemotherapies is very narrow, potential risks and benefits need to be meticulously evaluated.