Do Sharks Really Not Get Cancer?

According to a popular theory, sharks don’t get cancer, so medicines made from shark cartilage can prevent cancer in people. But there are some big flaws in that thinking.
A great white shark.
A great white shark. / Mark Chivers/Moment/Getty Images

Take shark cartilage, the doctor on the daytime talk show recommends. As the thinking goes, sharks don’t get cancer, so the pills will keep you from getting it, too.

The pills are based on the fact that shark cartilage has demonstrated anti-angiogenic properties—that is, it slows or stops the development of blood vessels. Since tumors need networks of blood vessels to survive and grow, cutting off vessel growth should starve, shrink, and destroy a tumor. It seems to work for the sharks, argues 1990s best-sellers like Sharks Don’t Get Cancer: How Shark Cartilage Could Save Your Life and Sharks Still Don’t Get Cancer.

There are two big problems here, though. The first is that, while some anti-angiogenesis therapies and medications are effective and have been approved by the FDA for treating cancers, cartilage pills aren’t one of them. The pills don’t make good on the claims made about them. Cartilage pill makers base their promotions around a very small body of research that shows, according to a 2005 study published in the scientific journal Cancer, only a “modest ability to slow the growth of new blood vessels in laboratory cell cultures and in animals” and, in a series of trials that have been critiqued for poor controls and methodology, mixed results in humans. Another study suggested that a group of patients with advanced cancer went into remission thanks to cartilage treatment, but the results weren’t published in a peer-reviewed journal and the National Cancer Institute later called the study “incomplete and unimpressive.” 

The overwhelming majority of peer-reviewed and published evidence goes against shark cartilage’s supposed anti-cancer abilities. In numerous trials in both humans and mice, researchers have concluded that shark cartilage provides no benefit against cancers. Both the FDA and FTC have pulled shark cartilage products from the market and/or fined their manufacturers for making unproven claims about anti-cancer properties.

But ... Do Sharks Get Cancer?

The second problem is that the very foundation of the cartilage pill cure—the idea that sharks don’t get cancer—isn’t true.

Sharks get cancer. We knew that even before people started claiming that they didn’t and using that to market cartilage pills. The first tumor recorded on a cartilaginous fish was found on a skate in 1853, and the first found on a shark followed in 1908. Since then, researchers have found some 40 instances of cancerous tumors in at least 24 shark species. These tumors were found in various parts of the body—including in the cartilage and on the face of an unfortunate great white shark.

So, yes, there are sharks with cancer, and using bits and pieces of them in pills won’t do anything for you.

A version of this story was published in 2014; it has been updated for 2024.

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