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Summary: A well-designed study comparing a shark cartilage powder with a placebo (a dummy supplement) found that the shark product did not help people with advanced cancer live longer. Many people dropped out of the study early. The shark cartilage also did not improve participants' overall quality of life, and may have made some people feel worse. The full report was published in the May 23 online version of the journal Cancer.

Why it's important: Shark cartilage supplements are still sold in many US stores and through dozens of commercial sites on the Internet. And while supplement companies are not allowed to claim that their products can treat medical illnesses like cancer, many "natural" health Web sites still carry claims that shark cartilage can help fight cancer. These unproven claims could mislead cancer patients into using a product that does not work.

What's already known: Research has shown that some types of shark cartilage can slow the growth of new blood vessels (a process called angiogenesis) in lab tests and in animal studies. Without an expanding supply of blood, the growth of cancer cells into tumors should slow down, too.

Before this trial began, studies of shark cartilage use by people with cancer were inconclusive or poorly designed. However, public interest was very high due the book Sharks Don't Get Cancer and a 1993 report on TV's 60 Minutes program, which showed cancer patients in Cuba apparently doing well after treatment with shark cartilage. The research in Cuba was never published.

"Basically, there was some rationale for its use," said Charles Loprinzi, MD, lead researcher on the study and a professor at the Mayo Clinic College of Medicine. He added, "It decreases angiogenesis and [there was] anecdotal information about it. We set out to say, 'Is there a benefit and can patients tolerate it?'"

What was found: Researchers from the North Central Cancer Treatment Group (NCCTG) ran a scientifically-rigorous, double-blind study of 83 people with advanced, incurable breast or colon cancer who received standard cancer care. They were randomly assigned to get either a shark cartilage powder mixed into a drink 3-4 times a day (up to 96 grams) or an inactive (placebo) powder that looked and smelled like the real thing.

By 1 month, only about half of the patients remained in either group. "A lot of patients could not tolerate it for long," said Loprinzi. "The main problem was the taste and smell of the product." Researchers compared survival and quality of life data for both the placebo group and the shark cartilage group.

"It did not prolong survival and there was no evidence that it improved quality of life," explained Loprinzi.

The bottom line: Cancer patients considering taking shark cartilage supplements should take into account the lack of evidence of benefit before doing so. Loprinzi said it's not all that surprising when a treatment that has to get through the digestive system fails to work. Another clinical trial of a liquid form of shark cartilage is still in progress, according to Ted Gansler, MD, director of medical content for the American Cancer Society.

Gansler added that other drugs with anti-angiogenesis actions look more promising. "Drugs that inhibit the growth of blood vessels to nourish cancers are now already FDA–approved and in late stage clinical trials."

"The combination of laboratory research followed as appropriate by clinical trials is the best way to distinguish treatments that are safe and effective from those which are not," said Gansler.

Citation: "Evaluation of Shark Cartilage in Patients with Advanced Cancer." Published online May 23, 2005 in Cancer (Print issue: July 1, 2005). First author: Charles L. Loprinzi, MD, Mayo Clinic and Mayo Foundation, Rochester, Minnesota.