Can Sharks Get Cancer?

In this installment of Ask a Marine Biologist, Dr. David Shiffman tackles a frequently asked question about sharks.

Question: Can sharks get cancer?

Answer: Yes, sharks absolutely get cancer. Cancer in sharks was first documented before the U.S. Civil War, and is not a new discovery. So no, conspiracy theorists in my Twitter mentions, cancer in sharks is in fact totally unrelated to Fukushima radiation. I remain stunned that so many people wrongly believe that the Fukushima nuclear reactor accident is responsible for every modern-day ill in the oceans—we’ve been dumping all kinds of crap in there for decades—but that’s a rant for another time.

Sharks have some pretty remarkable traits that have long attracted the interest of the medical research community, sure. These include sharks’ amazing ability to heal from wounds, their relatively strong immune system, and the presence of some antibiotic compounds in their liver. Some of this research might lead to treatments for all kinds of human medical conditions. However, just eating the ground-up dried shark pills sold by pseudoscientific snake-oil salespeople won’t cure cancer any more than me eating LeBron James would improve my very limited basketball skills.

The claim that sharks don’t get cancer is at best science fiction, and before anyone makes any Deep Blue Sea jokes, I’d remind you that in the movie, the Aquatica facility that used genetically engineered super-sharks for medical research was explicitly studying Alzheimer’s and other neurodegenerative conditions, not cancer, which is why they gave them giant super-shark brains. (God, no one pays attention to the classics anymore.)

My fear is that this myth, grounded in pseudoscience and perpetuated in books like the widely read Sharks Don’t Get Cancer (1992) and its 1996 follow-up Sharks Still Don’t Get Cancer, might give desperate people false hope and lead them to make bad decisions. People who have been diagnosed with a terrible disease (and their loved ones) are often willing to try anything to find a cure, no matter the cost, and unscrupulous people might try to sell them something they know doesn’t work. This is a pretty terrible thing to do, without even getting into how you probably shouldn’t kill threatened species of wildlife for a “cure” that doesn’t work.

Do sharks get cancer at a lower rate than other animals? That’s an interesting question, and the answer is that we don’t really know. The study I mentioned above explicitly points this out, noting that scientists just haven’t done a systematic comparison across all species of sharks yet. We probably never will do this because many species of sharks are pretty hard to keep in captivity in a biomedical lab. Regardless, the claim that sharks don’t get cancer at all is demonstrably nonsense, as is the related claim that eating bits of dried up shark will cure your cancer.

Ask a Marine Biologist is a biweekly column where Dr. David Shiffman answers your questions about the underwater world. Topics are chosen from reader-submitted queries as well as data from common internet searches. If you have a question you’d like answered in a future Ask a Marine Biologist column, or if you have a question about the answer given in this column, email Shiffman at WhySharksMatter@gmail.com with subject line “Ask a marine biologist.”

Dr. David Shiffman is a marine conservation biologist specializing in the ecology and conservation of sharks. An award-winning public science educator, David has spoken to thousands of people around the world about marine biology and conservation, and has bylines with the Washington Post, Scientific American, New Scientist, Gizmodo and more. Follow him on Twitter, Facebook and Instagram, where he’s always happy to answer any questions about sharks.