Administration of antineoplastic agents during cancer chemotherapy results in a much greater degree of oxidative stress than is induced by cancer itself and may overcome the antioxidant defenses of cancer cells, with the resulting lipid peroxides reducing or halting cancer cell proliferation and interfering with antineoplastic activity.
Supportive nutritional therapy with antioxidants during chemotherapy, which reduces the generation of lipid peroxides that results from the treatment, may overcome the growth-inhibiting effects of oxidative stress and maintain responsiveness to antineoplastic agents.
ROS are not involved in the mechanism of action of most anticancer drugs in current use (except bleomycin), hence it is unlikely that dietary supplementation with antioxidants can interfere with the mechanism whereby antineoplastic agents are cytotoxic to cancer cells.
Elena J . Ladas et al reviewed 31 observational studies of antioxidant status and cancer outcomes and 21 intervention trials of antioxidants among patients receiving chemotherapy with or without radiation for different malignancies.
Effects of supplementation on chemotherapy-related toxicities
12 clinical trials investigating the effects of antioxidant supplementation on chemo-related toxicities were documented.
In patients with ovarian cancer treated with cisplatin and cyclophosphamide, those who received 3 months of selenium supplementation had significantly higher (p<0.05) neutrophil counts and less nausea/vomiting, abdominal pain, weakness, malaise and anorexia than controls.
Selenium administration reduced cisplatin-induced nephrotoxicity in the acute stages (24 to 48 hrs), but not over long term (>72 hrs). One out of four trials investigating the effects of antioxidant supplementation on cardiac toxicity found that vitamin E with nifedipine prevented a decrease in left ventricular ejection fraction among patients on anthracycline-based therapy. However, vitamin E was not shown to prevent chronic doxorubicin-induced cardiotoxicity.
Legha and associates reported that vitamin E did not compromise the antitumour activity of doxorubicin. Clinical studies showed that CoQ10 may provide a safe and effective means of reducing or preventing the development of the cardiomyopathy associated with chronic administration of anthracyclines. Antioxidant supplemetation had no significant effect on mucositis, alopecia or skin ulceration.
Effect of antioxidants on recurrence rates and survival
3 out of 6 clinical trials found no effect on recurrence or survival. Two reported a survival benefit with supplemetation and one study reported significant findings (reduction in recurrence) in the short term (year 1) but not in overall survival.
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