The promotion of ground-up shark cartilage as a cancer “cure” over the last decade has come at the expense of cancer patients and sharks alike, according to researchers.

Powdered shark cartilage first began sailing off health-food store shelves after the 1992 publication of I. William Lane’s book “Sharks Don’t Get Cancer,” which popularized the notion that substances in shark cartilage protect the animals from developing cancer, and can do the same in humans.

A central problem with that premise, however, is that sharks do get cancer. And no one knows, as Lane has argued, if that’s a rare occurrence, according to Gary K. Ostrander, a research professor in the departments of biology and comparative medicine at Johns Hopkins University in Baltimore.

In the journal Cancer Research, Ostrander and his colleagues detail 42 known cases of tumors in sharks and related species, including three previously unreported cases of cancer in spiny dogfish and tiger sharks. It even appeared that the animals’ cartilage itself was vulnerable to tumors.

The true incidence of cancer in sharks is not known, the researchers say, but even if it is rare, the cartilage-cure theory holds no water.

The Lane book, Ostrander said in an interview with Reuters Health, “created an illusion.”

That illusion, he explained, involves a distortion of research that has identified substances in cartilage from some animals - including sharks and calves - that seem to block the growth of new blood vessels. New blood vessel formation, known as angiogenesis, is vital for a tumor’s survival and growth, and researchers have for years been looking for ways to treat cancer by blocking angiogenesis.

However, the notion that swallowing powdered shark cartilage could pass along any molecules that block angiogenesis is “illogical,” according to Ostrander. He said that a colleague once likened the idea to eating tissue from a jackrabbit in order to run faster.

Moreover, Ostrander and his colleagues note in the report, no well-designed, controlled trials have shown cartilage extracts to be effective against cancer.

It’s still possible, according to Ostrander, that substances within shark cartilage may be of use in cancer treatment, but first they must be isolated, highly purified and researched. This could also allow for any beneficial compounds to be synthesized, rather than harvested from sharks.

Dwindling shark populations, Ostrander’s team believes, are a sign of the successful marketing of shark cartilage as medicine. “Shark populations are crashing in some areas because of this,” he said.

Ostrander and his colleagues blame the situation on the failure of scientists, the media and society as a whole to “deal with pseudoscience.”

“The increased power of electronic media,” they write, “has increased the potential harm of pseudoscience, turning what would otherwise be quaint cultural curiosities into potentially serious societal and ecological problems.”

SOURCE: Cancer Research, December 1, 2004.