Guess What? Sharks Do Get Cancer

From the WebMD Archives

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.

Lane Labs produces a popular shark cartilage product called Benefin. Researchers are not the only group going after the product: In December, the FDA sought a permanent injunction against the marketing of Benefin for "unproven claims for unapproved drugs." The government filed suit against the company, charging that it unlawfully promoted and marketed the product as a treatment for cancer.

The FDA says the products can be tested as potential cancer therapy in clinical trials, but must now be marketed as dietary supplements.

Steel says the claims against Lane Labs and shark cartilage are unjustified.

"We make absolutely no claims as to its effect on cancer or any other disease," she tells WebMD. "What we do do is provide people with research information ... and give them the whole picture about what has been going on with shark cartilage so that they can make their own decisions based on the medical evidence."

She points to one 600-patient clinical study planned by the National Institutes of Health's National Cancer Institute in conjunction with the Mayo Clinic. The cancer study, she says, will use shark cartilage from Lane Labs.

William Lane responded to the study by Harshbarger and Ostrander in writing, calling their conclusions "nonsense." Lane says in his book that he also documented 30 tumors found among 7,500 shark records catalogued by the Smithsonian.

Both Lane and Steel also dispute the ecological claims, saying sharks are killed for their meat, and the cartilage is a byproduct of that harvesting.

James Dillard, MD, is the medical director for Oxford Health Plan's alternative medicine program in New York. He says it's important not to dismiss all alternative approaches "out of hand."

"Do we think that shark cartilage is going to be the cure for cancer? No, probably not, but honestly, we do need to see the results of [the clinical trial] that's going to be coming out, just to put the nail in that coffin," Dillard tells WebMD.

The point may be moot, he says, because ingesting shark cartilage is an ineffective process. He says people "forget this thing called the gut, which just shreds everything."

So, are there elements to sharks that may lead to therapies for humans? Perhaps there are. Are sharks less vulnerable to cancer because of something like their immune system, or is it just -- as suggested by Ostrander and Harshbarger -- that sharks live in the open ocean, away from cancer-causing substances?

Only time -- and science -- will tell, Dillard says.

  • The popular idea that sharks don't get cancer has spawned an entire industry of supplements containing ground-up shark cartilage. Researchers say this notion is a myth.
  • One researcher says that the use of shark cartilage is bad for cancer patients because it gives them false hope, and bad for the ecosystem because so many sharks, which are top-level predators, are being killed.
  • Clinical trials have shown that shark cartilage has no benefit for cancer patients, but another trial, sponsored by the National Institutes of Health, is under way.