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Guess What? Sharks Do Get Cancer

WebMD Health News

April 5, 2000 (Atlanta) -- Sharks have captured people's imagination, for better or worse, since men drew sea serpents and dragons on maps. Until recently, little has been known about them -- an open invitation to myth.

Now, science seems to be shattering one legend about the fabled fish: that they never get cancer -- a notion that has prompted thousands of cancer patients to ingest shark-cartilage supplements. In a study discussed at a recent cancer research meeting, scientists documented about a dozen cases of apparent cancer in sharks -- including a cancer of the cartilage.

Scientists have known for some time that sharks get cancer, researcher Gary Ostrander, PhD, tells WebMD. "Why this is significant is that for some time now, there's been a myth that's continually being perpetuated that sharks don't get cancer, and as a result of that, there's a huge industry that's sprung up of selling shark cartilage," he says.

There is a reason this came about, says Ostrander, a professor of biology at Johns Hopkins University. "Early ... studies in the '80s showed properties of the shark, in cartilage, that prevent blood vessels from growing. ... [C]learly tumors need this, but it's just a big leap from that to shark cartilage [supplements]."

Ostrander says the use of shark cartilage supplements is problematic for two reasons: It gives cancer victims false hope, and "people are killing sharks and harvesting sharks around the world at a rampant rate."

At the meeting, Ostrander and study co-author John C. Harshbarger, PhD, presented documentation of more than 40 benign and cancerous tumors in sharks and close relatives such as skates and rays.

Harshbarger says that among the 40 examples, some of which date back about 90 years, are 11 or 12 he believes would be considered cancer. There was even one case of a cartilage tumor, albeit benign. Harshbarger is director of the Registry of Tumors in Lower Animals at George Washington University.

Carl Luer, PhD, senior scientist at the Mote Marine Laboratory in Sarasota, Fla., says he's been trying to shed light on the mystery surrounding the low rate of cancer in sharks for 21 years. Currently, he's focusing on what role the immune system might play.

He notes, as did the researchers, that few of the examples presented by Ostrander and Harshbarger were malignant tumors.

"The scientific community has for some time stated that the incidence is low, as opposed to nonexistent," he says, "but I think that the promoters of some of the food supplements that are out there are the ones that are really misstating the case."

A big impetus to the interest in using shark cartilage to treat cancer came from a 1992 book titled Sharks Don't Get Cancer by biochemist I. William Lane, PhD. The book, which Ostrander calls a "very, very poorly written, very selective interpretation of a lot of people's data," is actually "sort of the underlying subject of this study," Joyce Steel, spokesperson for Lane Labs in Allendale, N.J., tells WebMD.

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