For a long time, people believed something remarkable about sharks.

They believed sharks never get cancer.

This idea became so popular that some companies even started selling “shark cartilage” supplements, claiming it could prevent or cure cancer in humans.

It sounded convincing.

Sharks are ancient creatures.
They’ve survived for hundreds of millions of years.
Their bodies are mostly made of cartilage instead of bone.

So people assumed their biology must contain some kind of natural cancer-proof system.

But the real story is more complicated.

The belief that sharks don’t get cancer mainly started in the 1990s.

Some early researchers noticed that very few cancer cases had been documented in sharks, and that observation slowly turned into a much bigger claim: that sharks were essentially immune to cancer.

The idea spread quickly.

Books were written about it.
Supplements were marketed around it.
And the myth stuck.

But the problem was simple.

Very few sharks had actually been studied.

As marine biologists began studying sharks more closely, they started finding something important:

Sharks can get cancer.

Tumors have been discovered in multiple shark species, including cancers in organs, tissues, and even cartilage.

So the original claim wasn’t true.

Sharks are not cancer-proof.

However…

They do appear to get cancer less frequently than many other animals.

And that’s where things get interesting.

Researchers think sharks may have strong DNA repair mechanisms.

Every time a cell divides, there’s a chance for genetic mistakes to happen.
Those mistakes can sometimes turn into cancer.

But sharks seem to have highly efficient systems for detecting and repairing damaged DNA before it becomes a problem.

Some studies have also found that sharks may have genes that help them maintain genome stability — meaning their genetic code stays more stable over time.

This doesn’t make them immune.

But it may make them better at preventing dangerous mutations from spreading.

Scientists are very interested in these mechanisms because understanding how animals resist cancer could eventually help medical research.

But the idea that shark cartilage can cure cancer?

That part has been thoroughly tested and there’s no scientific evidence supporting it.

The myth turned out to be stronger than the science.

The Bigger Lesson

Nature is full of creatures that seem almost indestructible.

But when we look closely, the truth is usually more nuanced.

Sharks aren’t cancer-proof.

They’re just very good at managing the risks that come with living for a long time.

And that alone makes them fascinating.

If you enjoy understanding the why behind things that seem ordinary,
there’s a lot more like this coming.