Shark Cartilage

Shark Cartilage

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The rising popularity of shark cartilage extract as an anti-cancer treatment is a triumph of marketing and pseudoscience over reason, with a tragic fallout for both sharks and humans, according to a Johns Hopkins biologist writing in the December 1, 2004, issue of Cancer Research.

"Since shark cartilage has been promoted as a cancer cure, not only has there been a measurable decline in shark populations, but cancer patients also have been diverted from proven, effective treatments," said Gary K. Ostrander, a research professor in the departments of Biology and Comparative Medicine at The Johns Hopkins University.
In the paper, titled "Shark Cartilage, Cancer, and the Growing Threat of Pseudoscience," Ostrander writes, "Crude shark cartilage is marketed as a cancer cure on the premise that sharks don't get cancer. That's not true, and the fact that people believe it is an illustration of just how harmful the public's irrationality can be."

In fact, Ostrander's paper details more than forty examples of tumors in sharks and related species, dating back to the mid-1800s. In the paper, Ostrander and a team of researchers from the Registry of Tumors in Lower Animals not only dissect what they call the "fallacious arguments" that have successfully convinced desperate cancer patients to purchase and ingest crude shark cartilage extract, but they also call for society to become more scientifically literate and, thus, less vulnerable to skillfully mass-marketed illogical claims.

"People read on the Internet or hear on television that taking crude shark cartilage extract can cure them of cancer, and they believe it without demanding to see the science behind the claims," Ostrander said. "This shows how the electronic media have increased the potential harm of pseudoscience, turning what would otherwise be quaint cultural curiosities into potential serious societal and ecological problems. The only way to combat this is to ensure that government leaders and media professionals receive adequate scientific training based on reason, and that they also develop critical thinking skills."

Ostrander traces the popularity of crude shark cartilage as a cancer treatment and preventive measure to I. William Lane's 1992 book titled Sharks Don't Get Cancer, which was further publicized by the CBS News program 60 Minutes in 1993. Though Lane acknowledges in the book that sharks do, in fact, get cancer, he bases his advocacy of crude cartilage extracts on what Ostrander calls "overextensions" of some early experiments in which the substance seemed to inhibit tumor formation and the growth of new blood vessels that supply nutrients and oxygen to malignancies.
"The fact is that it is possible that highly purified components of cartilage, including from sharks, may hold some benefit for treatment of human cancers," Ostrander said. "The key will be to isolate these compounds and design a way to deliver them to the site of the tumor. Lane and others ignore these existing barriers and suggest that consuming crude cartilage extracts by mouth or rectum could be curative of all cancers--an approach for which there is no scientific basis." --Johns Hopkins University

For more than a decade, shark cartilage has been touted as a rich source of anticancer agents. Although shark cartilage extracts have not yet shown efficacy against cancer in controlled clinical trials, the general public--especially cancer patients desperate for a cure--appear to have embraced the idea. Ecologists fear that continued growth of the shark cartilage industry could have a negative impact on shark populations, which are vulnerable to overfishing.

One of the main justifications made for studying the anticancer activity of shark cartilage is the assertion that sharks rarely develop cancer. Ostrander et al. describe evidence that this assumption may be incorrect. Gathering information from the National Cancer Institute's "Registry of Tumors in Lower Animals" and from the scientific literature, they identified 42 cases of tumors in sharks and their close relatives, about one-third of which were malignant. The authors point out the need for systematic surveys to determine the true incidence of cancer in sharks, and they discuss several alternative explanations for why sharks might have a low incidence of cancer, none of which require the presence of protective agents in cartilage.--PAK

Cancer Res. 64, 8485 (2004).