Fact or Fiction: Can Sharks Get Sick or Have Cancer?

Written by Samantha Stanich
Updated: July 27, 2023
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An old wives’ tale states that sharks can’t get cancer. However, this is a myth. Sharks can get sick and can get cancer. They are just like any other animal and vulnerable to parasites and a variety of illnesses.

There are at least 42 documented benign and malignant tumors in cartilaginous fish. These fish have cartilage skeletons rather than bones. Sharks are from the class Chondrichthyes, which means “cartilage fish”, as opposed to Osteichthyes, which are bony fish.

Shark in blue water

Sharks are amazing creatures, but they are not immune to cancer.

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Why Do We Think Sharks Can’t Get Cancer?

This myth started in 1970. Henry Brem and Judah Folkman of Johns Hopkins School of Medicine found that cartilage prevented the growth of new blood vessels into tissues. Angiogenesis is the creation of new blood vessels and is a crucial factor for malignant or cancerous tumors. A cancerous tumor needs nutrients and oxygen to grow. The tumor sends signals that stimulate more blood vessels to grow and carry blood. Doctors treat cancer with angiogenesis inhibitors to block this growth.

Brem and Folkman put live cartilage next to a malignant tumor in a rabbit. The tumor’s growth rate declined. Their research led other scientists to follow suit. Another researcher, Robert Langer, repeated Brem and Folkman’s experiment using shark cartilage. He reasoned that since sharks’ skeletons are composed entirely of cartilage, it would be an accessible source for potential use against cancer. Because just like the rabbit cartilage, the shark cartilage inhibited blood vessels from growing toward tumors, inhibiting tumor growth.

Then, in 1992, a best-selling book titled Sharks Don’t Get Cancer by Dr. I William Lane, added to the shark cartilage craze. The book claimed shark cartilage saved cancer patients and it was uncommon for sharks to have solid tumors. This claim brought instant fame to Lane. He had the “cancer cure,” and began selling shark cartilage pills. Many others followed Lane’s footsteps, and the result was devasting for sharks.

Why the Myth was Harmful to Sharks

As drug companies jumped on the bandwagon to sell “cancer-preventative” supplements, shark populations began to decline. A New York Times article states populations decline more than 70% since 1970 mainly due to overfishing. According to the IUCN Red List of Threatened Species, extinction threatens over one-third of shark species. So not only has this myth given false hope to cancer patients and diverted them from effective treatments, but it has added to the dramatic decline in shark populations.

In June 2020, cancer patients fined Lane’s company $1 million for false advertising. Unfortunately, stores still sell shark cartilage. It comes in powder or liquid form now. Shark cartilage is also advertised as a food or dietary supplement, and continues to be sold under the guise that sharks don’t get cancer.

Great White Shark breaching the sea surface after being lured to a cage diving boat by meat lures and wooden seal decoy, Gansbaai, South Africa

The decline in sharks is concerning because sharks help balance the ecosystem in our world’s oceans.

©Light and Vision/Shutterstock.com

What Sickness Affects Sharks?

Sharks do get cancer, along with other illnesses. Scientists found tumors in 23 different shark species. It would be naive to think that the pollution of the ocean doesn’t have a cancerous effect on marine life. In fact, sharks have high levels of mercury, microplastic, and other pollutants in their systems. Sharks are apex predators who ingest various prey. Their prey ingests mercury through algae, and sharks accumulate this mercury faster than they excrete it.

Sharks also get bacterial and viral infections and can suffer from parasites. Even though some species of sharks are one of the larger animals in the ocean, tapeworms and other parasites find them tasty. In fact, sharks are an incredible food and breeding source.

Caribbean Reef Shark swims over a shipwreck

Sharks are important predators and keep prey species populations at a healthy level.

©Greens and Blues/Shutterstock.com

Why Should We Continue to Study Sharks?

Sharks are basically living ancient artifacts. Their immune systems helped them survive over 400 million years on Earth. They have a natural resistance to diseases and viruses but are not immune to them. Their primitive immune systems may hold the key to how to improve treatments for humans. However, these animals are capable of getting sick and are not the ultimate answer to society’s cancer problems.

The photo featured at the top of this post is © iStock.com/ShaneMyersPhoto

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