Antioxidant supplementation and cancer patients receiving curative-intent chemotherapy

Much of the advice in the lay press regarding the benefits of antioxidants for people undergoing cancer treatment does not qualify or differentiate between curative and palliative cancer treatment or the type of cancer treatment involved.

Curative treatment of most tumour types is based on the administration of multiple cycles of regularly scheduled chemotherapy. Chemotherapy dose intensity, a function of dose and frequency of administration, has been shown to correlate with outcome for some tumour types in prospective clinical studies.1 For this reason, granulocyte colony-stimulating factor support is standard treatment in most curative treatments of breast cancer as it enables dose intensity to be kept constant, which significantly improves disease-free and overall survival.2 Antioxidant supplements may compromise cancer patients’ chemotherapy dose, and therefore dose intensity, by protecting tumour cells from oxidative damage.3,4 The primary mechanism of action of many chemotherapy agents, such as the alkylating agents, anthracyclines, podophyllin derivatives, platinum compounds and camptothecins, is the generation of reactive oxygen species, which induces apoptosis in cancer cells. Antioxidant supplements may inhibit reactive oxygen species, thereby protecting cancer cells from death.3,4

Although an often-cited 2007 systematic literature review to support antioxidant use proposed no evidence of significant decreases in chemotherapy efficacy associated with antioxidant supplementation, many of the 19 included studies were small and underpowered, only four studies were double-blinded, and the presented survival data were premature.5 As most of the study subjects included in the review had advanced or relapsed disease, the results are not applicable to patients with earlier, more chemo-sensitive disease such as the curative population.5

To date, there is not sufficient evidence to determine whether antioxidants exert a positive or a negative effect with adjuvant cancer treatment.6 However, considering the narrow therapeutic window of anticancer drugs, relatively small changes in dose intensity that may occur due to antioxidant activity could compromise treatment effectiveness. This is especially important in the curative-intent patient population, because reducing the effective chemotherapy dose intensity may adversely affect disease-free and overall survival.