Cancer Fighter Fails Big Test

New research sheds doubt on the benefits of selenium in connection with lung cancer prevention. A 10-year study led by researchers at the MD Anderson Cancer Center showed no benefits from the essential trace mineral.

Selenium is hypothesized to work by lessening the negative impact of free radicals in the body. The mineral helps make special proteins, called antioxidant enzymes, which play a role in preventing cell damage. Studies have shown that selenium levels are linked to a reduced risk of prostate and other cancers.

Consequently, for years, many thought selenium was a potential lung cancer cure, though there has been speculation that extremely high levels of selenium may actually increase the risk of cancer.

Plant foods, such as vegetables, are the most common dietary sources of selenium. How much selenium is in the vegetables you eat depends on how much of the mineral was in the soil where the plants grew, according to Medline Plus, a service of the U.S. National Library of Medicine and the National Institutes of Health.

Fish, shellfish, red meat, grains, eggs, chicken, liver, and garlic are all good sources of selenium. Meats produced from animals that ate grains or plants found in selenium-rich soil have higher levels of selenium.

Brewer's yeast, wheat germ, and enriched breads are also good sources of selenium, which is often available in multivitamin and mineral supplements.


Results from the decade-long study initiated by the Eastern Cooperative Oncology Group were presented at the American Society of Clinical Oncology's 2010 annual meeting by Daniel D. Karp, M.D., professor in the Department of Thoracic/Head and Neck Medical Oncology at The University of Texas MD Andersen Cancer Center.

“Several epidemiological and animal studies have long-suggested a link between deficiency of selenium and cancer development,” Karp says. “Interest and research escalated in the late 1990s after a skin cancer and selenium study, published in 1996, found no benefit against the skin cancer, but did suggest an approximate 30 percent reduction of prostate and lung cancers. Our lung cancer research and another major study for the prevention of prostate cancer evolved from that finding.”

Follow-up clinical studies investigating the naturally occurring mineral, however, have proven disappointing, according to MD Anderson, which provides cancer care at satellite locations in the greater Houston area.

The center seeks to eliminate cancer in Texas, the nation, and the world through programs that integrate patient care, research and prevention, and through education for undergraduate and graduate students, trainees, professionals, employees and the public. MD Anderson provides radiation treatment and medical oncology, along with a range of supportive services.

In 2009, the National Cancer Institute abandoned SELECT, an international study of more than 35,000 men investigating if either selenium or Vitamin E, alone or in combination, could reduce the risk of prostate cancer. Both treatments failed to exhibit any benefit.

Some 219,440 people were diagnosed with lung cancer in 2009 and 159,390 died from the disease, making it the leading cause of cancer death in both men and women, according to the American Cancer Society.

When lung cancer is caught as early as Stage One, and the tumor is surgically removed, about 80 percent of the cases can be cured. In this population, a chemoprevention agent is reportedly desirable, since the risk of recurrence in Stage One patients after surgery accumulates by 1 percent to 2 percent annually. By example, a patient’s risk of developing a new cancer at 10 years is about 10 percent to 20 percent, Karp says.

The study further reported that from 2000 to 2009, the International NCI-sponsored Phase III study enrolled 1,522 Stage One, non-small cell, lung cancer patients, all of whom had their tumors surgically removed and were cancer-free for at least six years after surgery.

Participants were randomly selected to receive either 200 micrograms of selenium or a placebo. The study’s primary endpoints were the reduction of the development of a new cancer, or second primary, and/or the recurrence of initial cancer.

The study was halted early after an interim analysis found the progression-free survival was superior in the placebo arm: 78 percent taking the placebo were alive without recurrence after five years, compared to 72 percent taking the selenium.

A total of 216 secondary primary tumors developed, of which 84 (38.9 percent) were lung cancers. Of those on selenium, 1.9 percent developed a second primary tumor after the first year, compared to 1.4 percent taking the placebo. In total, 3.66 percent of the participants in the selenium group developed a secondary primary tumor of any type after one year, compared to 4.1 percent in the placebo group.

We don’t really think that these results prove selenium is worthless; it just means the mineral does not appear helpful for lung cancer patients. More research will be needed to determine other regimens and to answer additional questions.

Possibly other treatments, from genetic engineering to synthetic cell experiments, also may lead to a better understanding of lung cancer and solving mysteries associated with the disease.

Scientific and medical research are never exact. The notion of a single treatment for all types of cancers seems unlikely.

Still, sometimes the search for treatments and cures in one area of focus leads to unintended but beneficial discoveries in other areas. This could be one of those times.

TechMan, WMB co-author, blogs about trends, issues and ideas affecting business, industry, health, technology and consumers.