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Antioxidants and Chemoradiotherapy |
Dietary supplements and antioxidants during and post-therapy are commonly used by cancer patients. There is evidence that antioxidants can reduce the effectiveness of cytotoxic therapy and radiation therapy. It is currently advised that during chemoradiotherapy, the use of antioxidants be avoided.
One of the rationales for the use of supplements and antioxidants is to reduce the toxicity of therapy. It is estimated that over 50% of cancer patients use supplements, vitamins, and antioxidants. Radiation therapy and some chemotherapy agents produce free radicals, which can be bound to vitamin C, E, and antioxidants, thus preventing the oxidative action that can damage cancer cells.
It is known that vitamin C and some antioxidants protect cancer cells from radiation and chemotherapy. Thus, the effectiveness of treatment is reduced, as well as possibly the toxicities. Oncologists, in general, feel the use of these substances is contraindicated.
There is also evidence that the use of carotenoids, beta-carotene, and vitamin A may promote the growth and occurrence of lung cancer rather than preventing lung cancer.
Clinical evidence suggests that the antioxidants may reduce the effectiveness of chemotherapy a few percentage points, which could relate to a large number of potential deaths because of the reduction in therapeutic activity.
In 1974, Cameron and Campbell showed the possibility that vitamin C could be useful in cancer therapy. Pauling and Cameron subsequently published survival benefits from vitamin C. (Cameron and Pauling, "Supplemental Escorbate in the Supportive Treatment of Cancer and Prolongation of Survival Times in Terminal Human Cancers." (Proceeding in the National Academy of Science, 1976: 73: 3685-3689.)
Two subsequent randomized, double-blind trials failed to confirm their claims and showed no objective improvement in survival or disease progression. Other studies in breast and other cancers with combination vitamins, minerals and antioxidants failed to show a difference when compared to placebo-treated patients.
The two trials, Alpha-tocopherol, beta-carotene cancer prevention study and the beta-carotene retinol! efficacy trial (CARETs), demonstrated increased risk for developing lung cancer in high-risk cohorts receiving beta-carotene supplementation. Other studies evaluating 400 IU of daily vitamin E versus a placebo had no significant effects on mortality in studies of prostate, lung, oral, colorectal, breast and melanoma. Those on vitamin E were more likely to also develop heart failure. This was also shown in the head and neck trial.
Thus, in conclusion, noting the principle of medicine primunmon nocere (do no harm) reflects the role of antioxidants with chemoradiotherapy and its harm. Patients should be advised accordingly.
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