A Creepy Mystery: Cancer and Large Animals#

Cancer feels really mysterious and, well, creepy. As folks have tried to figure out how to beat it, they stumbled upon something in biology that still doesn’t make sense: Turns out, really big animals seem almost immune to cancer. This is totally backwards from what you’d expect. You’d think the bigger something is, the more cancer it should get.

To get why this is so strange, you gotta look at what cancer actually is.

Getting a Handle on Cells and Cancer#

Think of our cells like tiny robots made of gazillions of little bits. They’re guided by just chemical reactions, building stuff, taking it apart, getting energy, and making copies of themselves. These complex chemical dances are called pathways – like networks upon networks, all tangled up. Even smart scientists can barely grasp them all.

Normally, they work perfectly. But over many years, with trillions of these reactions happening in thousands of networks, things are bound to go wrong. It’s not a question of if a mistake will happen, but when. Little errors pile up, and this amazing cellular machine gets messed up.

Our cells have backup plans, though. They have “kill switches” that tell them to just, well, commit suicide if they’re too broken. But these aren’t perfect either. If a kill switch fails, a cell can turn cancerous.

Most cancer cells get wiped out by our immune system pretty fast. But it’s a numbers game. Give it enough time, and a cell might rack up enough mistakes, slip past the defenses, and start making copies of itself.

Every animal has to deal with this problem.

The Strange Case of Size and Cancer#

Here’s where it gets weird: The size of cells is generally the same across different animals. A mouse’s cells aren’t smaller than yours. It just has fewer of them and doesn’t live as long.

Logically, fewer cells plus a shorter life should mean a much lower chance of mistakes or mutations leading to cancer, right? But that’s not what happens.

Check out these comparisons:

• Humans live roughly 50 times longer than mice.
• Humans have about 3,000 times more cells than mice.
• Yet, the rate of cancer is pretty much the same in both humans and mice.

Now, take it even further to giant creatures:

• Blue whales have about 3,000 times more cells than humans.
• But they don’t seem to get cancer at all, really.

This puzzling observation is known as Peto’s Paradox. It’s the baffling discovery that big animals have way, way less cancer than they have any right to.

Scientists have a couple of main ideas about why this is the case.

Idea 1: Evolve or Turn into a Cancerous Blob#

One thought is that it’s all thanks to evolution. When multi-celled life started developing about 600 million years ago, animals got bigger and bigger. More size meant more cells, and more cells meant more chances for things to go wrong and cells to get corrupted.

So, life had to get better at fighting cancer. The animals that didn’t develop better defenses just didn’t make it.

Cancer isn’t just one single mistake; it’s a whole process. It involves several specific mistakes and mutations happening in certain genes within the same cell. These genes are called proto-oncogenes. When they mutate, it’s bad news.

Here’s what some bad mutations can do:

• One mutation might make a cell lose its ability to kill itself.
• Another mutation could let it develop the ability to hide.
• Yet another might make it send out signals demanding resources.
• Another one allows it to multiply super fast.

Luckily, these oncogenes have opponents: tumor suppressor genes. These genes try to stop those critical mutations from happening in the first place, or they simply order the cell to self-destruct if it’s too messed up to fix.

It turns out that larger animals have more of these tumor suppressor genes. This extra protection means that an elephant cell needs more mutations than a mouse cell to actually become a tumor. They aren’t totally immune, but they’re much tougher to turn cancerous.

This adaptation probably comes with some sort of trade-off, but scientists aren’t sure what it is yet. Maybe having more tumor suppressors makes elephants age faster later in life, or maybe it slows down how quickly their injuries heal. Nobody knows for sure right now.

But maybe the answer to the paradox is something else entirely…

Idea 2: Hypertumors (Yes, Really.)#

This second idea involves something called Hypertumors. They got this name based on the idea of hyperparasites, which are parasites that live on other parasites. Following that logic, hypertumors are essentially tumors of tumors.

You can think of cancer as a breakdown in teamwork. Normally, cells cooperate perfectly to build organs, tissues, or parts of the immune system. But cancer cells are selfish; they only care about themselves in the short term. If they’re successful, they form big clumps called tumors, which are basically huge collections of cancer cells that are tough to get rid of.

Building a tumor takes a lot of work, though. Millions or billions of cancer cells multiplying rapidly need tons of resources and energy. The amount of nutrients they can steal from the body becomes the main limit on how big they can grow. So, the tumor cells actually trick the body into building new blood vessels directly to the tumor to feed the very thing that’s trying to kill the body!

And here’s where the tricky nature of cancer cells might backfire on them. Cancer cells are unstable and keep mutating. Some of them mutate faster than their neighbors in the same tumor. If this keeps happening, eventually, one of the copies of copies of the original cancer cell might suddenly start acting like an individual again and stop cooperating with the rest of the tumor.

Just like the body, the original tumor suddenly becomes an enemy to this new mutant cell, because they’re all fighting for the same limited food and resources. So, these newly mutated cells can form a hypertumor. Instead of helping the original tumor, they do the opposite: they cut off the blood supply to their former buddies, which starves and kills the original cancer cells.

It’s literally cancer killing cancer.

This process could potentially happen over and over. And scientists think this might stop cancer from ever becoming a big problem in large organisms. It’s possible that big animals have more of these tiny hypertumors than we even realize, and they just don’t grow big enough for us to notice.

Think about it:

• A two-gram tumor is 10% of a mouse’s body weight.
• That same two-gram tumor is less than 0.002% of a human’s body weight.
• And less than 0.000002% of a blue whale’s body weight.

All three tumors require the same number of cell divisions and have the same number of cells. So, maybe an old blue whale is full of tiny cancers, but they just aren’t big enough to cause any trouble.

Still More Ideas, Still More Questions#

There are other ideas out there about why large animals might avoid cancer, like differences in how fast their bodies use energy (metabolic rates) or differences in how their cells are built (cellular architecture). But right now, we just don’t have all the answers.

Scientists are working hard on this problem. Figuring out how giant animals are so good at resisting cancer could open up whole new ways to treat it in us. Cancer has always been a huge challenge, but by starting to really understand things like Peto’s Paradox, maybe one day we can finally beat it.