Sharks and Cancer: Here’s What We Know

posted: 07/05/15
by: Danny Clemens

Editor's Note: I ran a story a few days ago about the use of shark liver oil in the cosmetic industry -- specifically, how shark liver oil is rich in squalene, a compound valued for its moisturizing properties. The article sparked an impassioned conversation on social media (yes, we read your comments!) about another controversial use of shark-derived products: cancer treatment. Many people believe that sharks are immune to cancer, and that a compound found in their cartilage can be used to prevent and treat cancer in humans. In response to reader inquiries, I dug into the history of shark-based cancer treatments to settle the debate once and for all.

Gray nurse shark
Klaus Stiefel via Flickr

First and foremost: sharks do suffer from cancer. Researchers have observed sharks of various species that have developed tumors, including a great white with a foot-long mass on its mouth. The shark's malady was described in detail as part of a November 2013 study in the Journal of Fish Diseases.

"The main take-home message from the study is that it adds to the growing evidence of tumor formation in sharks, contrary to popular belief that sharks do not suffer from such anomalies," remarked study co-author Rachel Robbins.

Scientists do concede, however, that the incidence of cancer in sharks (and other marine wildlife, for that matter) is relatively low compared to humans. However, cancer rates are much higher in marine animals that have been exposed to pollution -- as pollution has penetrated every last corner of the earth in recent decades, marine animal cancer rates have risen steadily.

How did this pervasive myth about shark immunity come about? Scientific American notes a 1970's study in which Johns Hopkins researchers found that "cartilage prevented the growth of new blood vessels into tissues". Since malignant tumors are blood-hungry masses, a compound capable of preventing the flow of blood to malignant tumors should stop tumors dead in their tracks, right? Subsequent studies replicated the results of the Johns Hopkins study in other animals, including sharks.

Shark cartilage as a cancer treatment broke into the mainstream in 1992, when a best-selling book detailed a doctor's questionable clinical trial using cartilage to treat cancer. Conducted in Mexico, the trial followed cancer patients who took oral doses of powdered shark cartilage, seemingly to fantastic results. The market for shark cartilage pills in the Western hemisphere exploded, and the belief that sharks are immune to -- and can cure -- cancer has continued to pervade pop culture through past two decades.

There's only one problem: with the exception of the "shoddy" Mexican study, there is almost no scientific evidence to back up these claims.

In recent decades, more than a dozen clinical studies have been conducted in the United States in an attempt to link shark cartilage treatments to cancer. Of those dozen, only seven have stood up to the peer-review process, and none showed compelling evidence that shark cartilage treatments were successful.

Why are these products on the market with such little science to back them up? The cartilage treatments aren't classified as drugs, but rather "dietary supplements", which, according to the National Cancer Institute, precludes them from "premarket evaluation and approval by the U.S. Food and Drug Administration (FDA) [...] unless specific disease prevention or treatment claims are made".

In fact, the FDA hasn't approved cartilage as a treatment for cancer -- or any other medical ailment, for that matter.

And, get this -- Lane Labs, the company behind the wildly popular 1992 book, has been subject to decades-long litigation from the Federal Trade Commission for truth in advertising disputes. The agency found that, "in addition to the unsubstantiated efficacy claims, the defendants falsely represented that clinical studies have shown that BeneFin and SkinAnswer are effective in preventing, treating, and curing cancer, and falsely represented that the Food and Drug Administration has evaluated the effectiveness of BeneFin".

The company was eventually ordered to stop producing its powdered cartilage product and pay a hefty settlement to its customers.

All things considered, it seems appropriate to conclude that there is little to no scientific evidence that shark cartilage is an effective treatment for cancer in humans.

That being said, researchers are still actively investigating the possibility of using proteins found in shark immune systems as vessels to deliver tumor-fighting drugs.


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