Today we take a look at the longstanding myth that sharks do not get cancer, a claim often touted by supplement vendors who sell shark cartilage. Scientists disagree.
The misconception that sharks do not suffer from diseases (including cancer) has been promulgated by doctors and supplement companies pitching shark cartilage as a cure for cancer and a remedy for many joint-related problems. There is, however, no verifiable study of any shark-related product as an effective treatment for any human ailments.
Spreading of the myth may be attributed to books written in the 1990s by Dr I. William Lane and Linda Comac entitled “Sharks Don’t Get Cancer” (1992) and the follow up “Sharks Still Don’t Get Cancer” (1996). The first book was also the subject of a segment by the news journal 60 minutes.
Just like humans and the rest of the animal world, sharks suffer from bacterial infections, parasites, and infectious disease. The theory that sharks suffer from cancer less frequently is also difficult to document as afflicted animals are often eaten by others oceanic predators or simply sink to the bottom of the ocean floor where they decompose.
Specific Shark Cartilage Claims
Shark cartilage is believed by some to prevent or slow the spread of cancer because of certain “antiangiogenic” properties that limit or prevent the vascularization (blood flow) to and from tumors. While shark and cow cartilage have both inhibited tumor growth in some lab studies, they have not been shown to treat or benefit human illness.
In August of 2003, National Geographic featured an article on shark cartilage and cancer. The article includes an interview with Carl Luer, a researcher with the MOTE Marine Laboratory Center for Shark Research who has been studying cancer in sharks for 25 years. Although Luer thinks sharks might have a lower incidence of disease, he calls the belief that sharks do not get cancer an unfounded viewpoint. Below is a quote from the article by Luer:
“You have people catching and killing millions of sharks, grinding up their cartilage, and making misstatements to try to convince people that eating it will make them cancer-free… Unfortunately, there is no logical reason to conclude that freeze-dried shark cartilage pills taken orally could “seek out” a malignant tumor in a cancer patient and inhibit the blood vessels feeding it… Also, there is no reason to think that shark cartilage contains anything which is not found in other animal cartilage.”
More than 100 million sharks are harvested annually for their fins or cartilage which is used in dietary supplements. Eventually this kind of harvesting may send some shark species to the brink of extinction and create havoc in delicate ocean ecosystems.
Cancerous Tumors Found on Sharks
Despite scientists knowing for more than 150 years that sharks do get cancer, the myth persists that the most misunderstood predator in the ocean is immune to disease.
According to a December 2013 article in NBC News (since removed from the web), a large tumor had been found on the lower jaw of a great white shark. The tumor, measuring over a foot long and a foot wide, was found on a Great White swimming near the Neptune Islands off South Australia. A bronze whaler shark was also recently photographed with a mass protruding from it’s head along with several smaller masses found along the length of its body.
The article features information from a science study on shark tumors which appeared in the Journal of Fish Diseases, and includes a brief interview with Rachel Robbins, a shark biologist and co-author of the study. In an interview with LiveScience, Robbins is quoted as saying, “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.”
In all, scientists have now documented tumors on 23 species of sharks.
Sharks are not immune to cancer or the other maladies that affect the rest of the animal kingdom. In turn, there is no current scientific evidence that shark cartilage can treat or cure cancer in humans.
Select Scientific Studies on Shark Cartilage and Cancer
- Shark Cartilage, Cancer and the Growing Threat of Pseudoscience
- Evaluation of shark cartilage in patients with advanced cancer: a North Central Cancer Treatment Group trial
- First reports of proliferative lesions in the great white shark, Carcharodon carcharias L., and bronze whaler shark, Carcharhinus brachyurus Günther
Updated June 7, 2016
Originally published April 2014