Beta-Carotene Safe With Radiotherapy for Prostate Cancer

Low-dose beta-carotene supplements do not increase the risk of metastases or cancer mortality in men undergoing radiation therapy for prostate cancer, research shows.

The findings, based on a prospective analysis of 383 participants in the Physicians' Health Study (PHS), is "reassuring," lead author Dr. Danielle N. Margalit from the Dana Farber Cancer Institute in Boston told Reuters Health.

However, she added, "The study cannot be directly used to comment on the safety of other antioxidants, or for other cancers."

Dr. Margalit reported the findings in Miami Sunday at the American Society of Therapeutic Radiation Oncology's annual meeting.

Concerns had been raised that patients taking antioxidants during radiation therapy might be at increased risk of treatment failure, given that the supplements might counteract the pro-oxidant effects of radiation, Dr. Margalit explained in an interview.

The largest study to suggest this might be the case found that among head and neck cancer patients randomized to placebo or beta-carotene plus vitamin E, smokers who took the antioxidants were at increased risk of disease recurrence.

In the current study, Dr. Margalit and her colleagues looked at PHS participants having radiotherapy for prostate cancer who had been randomized to take 50 mg of beta-carotene on alternate days or placebo.

During a median of 10.5 years of follow-up after radiation therapy, there was no significant difference between the groups in the risk of the study's primary endpoints, death from prostate cancer or bone metastases, according to the research team.

The hazard ratio for lethal prostate cancer was 0.72 for the beta-carotene group versus the placebo group (P=0.24), and the difference remained non-significant after adjustment for age at radiation therapy, prostate specific antigen level, Gleason score, and clinical stage.

At 10 years, 92% of men in the beta-carotene group and 89% in the placebo group remained free of prostate cancer recurrence.

Fewer than 5% of patients in the study smoked, so Dr. Margalit and her team were not able to look at whether beta-carotene might have a different effect in smokers.

The issue of whether taking antioxidants during radiation therapy can be harmful is "definitely very controversial," Dr. Margalit said. High-dose antioxidant supplements are often marketed to patients undergoing radiation, she added. "We do find that some patients spend quite a lot of money buying high-dose antioxidant products. This study does not make any comment on the safety of these products."

At Dana Farber, she added, she and her colleagues recommend that patients take a standard multivitamin. The findings lend support to this recommendation, Dr. Margalit said, and also show that patients on radiation therapy need not be afraid to eat antioxidant-rich fruits and vegetables.
She and her colleagues are planning a similar analysis of PHS results to determine if vitamin C and vitamin E may influence the effectiveness of radiation therapy in prostate cancer patients, once a similarly long follow-up period has been reached for the second part of the study.