Shark Cartilage Quackery

The 1992 publication of William Lane's book, Sharks Don't Get Cancer, sparked a heated controversy between money-grubbing opportunists and medical orthodoxy. Although sharks do, in fact, occasionally develop cancer, shark cartilage was promoted as a natural "cancer cure" and all around wonder drug. In 1995, the world market for shark cartilage products exceeded US$ 30 million. Today, dozens of such products are on the market. Is there any evidence that shark cartilage is effective against cancer?

A provocative 1983 paper by oncologists Anne Lee and Robert Langer reported that two glycoprotein compounds from shark cartilage appeared to prevent tumor angiogenesis (formation of new blood vessels around cancerous growths) in tissue cultures. Since then, numerous papers have reported similar angiogenic properties of shark cartilage in vitro (literally, "in glass", meaning: in a laboratory container). In principle, this mechanism could be helpful in treating cancer in humans.

Unfortunately, there is no conclusive evidence that shark cartilage preparations sold as 'food supplements' do any good against cancer in the human body. As shark cartilage products are taken orally, it seems unlikely that the two glycoproteins allegedly responsible for angiogenic activity reach the blood stream at all, since such large, complex molecules are not usually absorbed by the intestinal tract. However, some macromolecules can cross the intestinal lining and thus may find their way to a solid cancer via the blood circulation. But even if this is true, many of the commercially available shark cartilage 'food supplements' contain only binding agents or fillers with no angiogenic activity.

No reliable dose-response data exist nor do studies confirming that the supposedly angiogenic glycoproteins are taken up and transported by the human blood circulation. The ultimate test of the efficacy of any drug must be the clinical trial. But, to date, no well-controlled clinical study has been published that demonstrates the efficacy of shark cartilage 'food supplements' against cancer.

According to a 1998 report by E. Ernst in the respected medical journal The Lancet, the U.S. National Cancer institute began a clinical trial of shark cartilage against tumors in 1994, but it was terminated when each batch of shark cartilage provided by advocates of the controversial treatment was found to be contaminated. Ernst's Lancet article goes on to state that preliminary results were reported from a clinical trial conducted in the U.S.: 50% of cancer patients who took about 100 mg of dried shark cartilage powder daily reported, "improvements in quality of life and appetite and a reduction in pain." While details of these studies have been debated by shark cartilage advocates in a subsequent letter to The Lancet, it is worth noting that no clinical study demonstrating the efficacy of shark cartilage as an anti-cancer agent has been published in a peer-reviewed medical journal.

Cancer patients are understandably desperate for any treatment that enhance their quality or quantity of life. In their search for a cure, those diagnosed with cancer often turn to so-called 'complementary' or 'alternative' medicine. Unfortunately, many purported alternative cancer treatments are at best highly dubious and at worst border on the cruelest sort of medical quackery. While there is absolutely no clinical evidence that shark cartilage offers any benefit to cancer patients, there is some evidence that it may actually do harm.

Physicians should advise their patients accordingly, and patients should be aware that many advocates who claim 'miraculous' properties for the shark cartilage products they sell may be motivated more by economic opportunism than by altruistic humanitarianism.

 

ReefQuest Centre for Shark Research
Text and illustrations R. Aidan Martin
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