Selenium Trial Fails to Show Prevention Benefit

Results of a phase III study that lasted 10 years demonstrate that selenium does not prevent lung cancer. The study, presented at the annual meeting of the American Society of Clinical Oncology this past June, showed that daily supplements of selenium did not prevent recurrences or new primary cancers in early-stage lung cancer survivors. The trial, dubbed ECOG E5597, was stopped early when preliminary results showed the supplement offered no benefit in progression-free survival.

Past animal and epidemiological studies had suggested that a deficiency of selenium, a dietary supplement, was associated with cancer risk. An earlier skin cancer study suggested it had preventive effects in lung, colorectal, and prostate cancers. However, the SELECT study (Selenium and Vitamin E Cancer Prevention Trial), published in 2009, produced negative results after examining selenium and vitamin E for prostate cancer prevention.

The E5597 lung cancer trial also had disappointing results. Of the 1561 individuals who underwent surgery for stage 1 lung cancer, patients were randomized to receive either selenium or a placebo. The selenium group actually had a slightly higher incidence of cancers, but the difference was not statistically significant, meaning it could be due to chance. Overall survival in the selenium group was also slightly lower.

Daniel Karp, MD, lead investigator of the study, said during his ASCO presentation that former and current smokers had a higher rate of developing another cancer while on selenium than never smokers. Karp, a professor of thoracic/head and neck medical oncology at M.D. Anderson Cancer Center in Houston, explained the supplement could actually work against individuals who have a smoking history because of the tobacco carcinogens. And while a slight improvement in five-year overall survival appeared in the 94 never-smokers involved in the trial, Karp said the difference was too small to be significant, “but this is the one group where the selenium actually seemed to show at least a slight trend toward benefit in survival.”

These findings suggest that future studies looking at supplements for prevention may be conducted in more select groups of patients. It also shows that an association of a deficiency of a certain factor or vitamin with cancer does not necessarily mean that replacing it will change the risk — the deficiency might be reflection of cancer risk but not causing it. Also, individual components may not be as important as balanced intake of numerous dietary factors. This is being explored with vitamin D, where deficiency seems to be associated with breast cancer recurrence risk, but experts are not recommending routine supplementation of vitamin D without prospective trials. “We have to find better targeted ways…the new studies are going to have to be more biologically based,” Karp said.