Danielle N. Margalit, MD
Men who take the dietary antioxidant beta-carotene while they are undergoing radiation therapy for prostate cancer do not have an increased risk of prostate cancer death or metastases, new data suggest.
The investigators had believed that the use of a supplemental antioxidant such as beta-carotene might weaken the oxidizing effect of radiation therapy and reduce treatment efficacy, thereby potentiating cancer recurrence.
Danielle N. Margalit, MD, Dana-Farber Cancer Institute, Boston, Massachusetts, and colleagues conducted a prospective study of Physicians’ Health Study (PHS) participants who received radiation therapy for prostate cancer while randomized to receive either 50 mg of beta-carotene on alternate days, or placebo. The landmark PHS study was started 30 years ago to determine the benefits and risks of aspirin and betacarotene in the primary prevention of cardiovascular disease and cancer.
The primary endpoint of the present analysis was time from the start of radiation therapy to lethal prostate cancer, defined as the date of death from prostate cancer or participant-reported bone metastases among living participants.
With a median follow-up of 10.5 years, there was no significant difference between the risk of lethal prostate cancer with the use of beta-carotene versus placebo during radiation therapy (hazard ratio = 0.72; 95% CI, 0.42-1.24; P
After controlling for patient age at the time of radiation therapy, prostate-specific antigen serum level, Gleason score, and clinical stage, the difference remained nonsignificant.
The 10-year freedom from lethal prostate cancer was 92% (95% CI, 87%-95%) in the beta-carotene arm and 89% (95% CI, 84%-93%) in the placebo arm.
Margalit et al identified as study strengths the inclusion of randomized exposure status, a large sample size, duration of follow-up, and the use of lethal outcomes as the outcome measure.
Potential limitations of the study included the availability of limited information about participants’ dietary sources of antioxidants, the use of concomitant androgen-deprivation therapy, and the rate of local tumor recurrence. As a result, the investigators were not able to examine the association between antioxidant use and local tumor r ecurrence after radiation therapy.
They also cautioned that their findings may not be extrapolated to all tumor types treated with radiation therapy given that “different tissues may have variable levels of amounts of antioxidants, tumor hypoxia, and other factors that may influence the interaction between antioxidants and radiation therapy.”
Additional research is needed to test the safety of other popular dietary antioxidants such as vitamins E and C for use with concomitant radiation therapy, the researchers noted.
Margalit DN, Kasperzyk JL, Martin NE, et al. Betacarotene antioxidant use during radiation therapy and prostate cancer outcome in the Physicians’ Health Study. Int J Radiat Oncol Biol Phys. 2012;83(1):28-32.