Supplementation may help cancer patients adhere to treatment.
CHICAGO—Antioxidant supplements can ease chemotherapy toxicity in cancer patients, perhaps enabling them to complete more treatments, according to researchers. This, in turn, could translate into better survival.
Lead investigator Keith Block, MD, co-founder and medical/scientific director of the Block Center for Integrative Cancer Treatment in Evanston, Ill., noted that there has been considerable debate over the past 15 years whether antioxidants interfere with the efficacy of cancer chemotherapy.
He and co-investigator Robert Newman, PhD, professor of cancer medicine at MD Anderson Cancer Center in Houston, systematically reviewed the medical literature to evaluate the effects of concurrent use of antioxidants with chemotherapy. “Overall, the review suggested overwhelming evidence that antioxidant supplementation does not interfere with the use of chemotherapy,” Dr. Block said.
Stressing the benefits of better compliance with chemotherapy, he pointed to a recent study of colon cancer patients showing that those who received a full five to seven months of chemotherapy had higher survival rates than those who only received one to four months of treatment, he pointed out. The mortality rates were twice as high among the 30% of patients who dropped out of the chemotherapy treatment early compared with the group that completed the course of treatment.
The investigators looked at 845 studies published between 1966 and December 2006 from six scientific databases. Of these, 30 trials involving 1,964 patients with a variety of cancer types met inclusion criteria. The vast majority of patients had advanced or relapsed disease.
The antioxidants evaluated were glutathione (nine studies), melatonin (six studies), vitamin A (one study), an antioxidant mixture (three studies), N-acetylcysteine (two studies), vitamin D (five studies), selenium (one study), L-carnitine (one study), Co-Q10 (one study) and ellagic acid (one study).
In 18 of the 30 studies, patients who received oral or IV antioxidant supplements experienced significantly lower toxicity than the control groups. Glutathione, melatonin, and vitamin D showed the most consistent and promising effects. Only the vitamin A study found significantly greater toxicity in the antioxidant group compared with controls, although this was not surprising because the toxicity of high-dose vitamin A is well documented.
Several studies found fewer chemotherapy dose reductions, fewer treatment interruptions, and less need to discontinue treatment prematurely among the antioxidant groups.
Of the 19 studies in the review that reported tumor response and/or survival rates, all but one of the antioxidant groups experienced the same or better re-sponse than the control group. No studies reported significantly worse survival in the antioxidant group.
“Each antioxidant had its own benefits,” Dr. Block said. “The glutathione studies demonstrated that the supplement groups were more likely to complete their prescribed number of chemotherapy cycles compared to the controls. The selenium studies showed more patients who were in the antioxidant arm were able to receive optimal chemotherapy dosing.”
Study findings were reported here at the American Society of Clinical Oncology annual meeting.