Why does cancer seem to be so rare in bats?

We get it. Bats are creepy.  

Sleeping on the ceiling, waking in the dark, flying like mice with naked skin wings; they seem to turn everything the other way round.  

Here’s another thing: some bats get better at repairing their DNA as they get older.  

That’s shocking enough to make a cancer researcher jump. Cancer starts with DNA mutations, which, in almost all animals, increase as the years go by, raising our cancer risk. From what we can tell, though, bats have a unique way of stopping that happening, making cancer a lot less common. Don’t mention vampires, but some species hardly seem to age at all. 

Then there’s also the fact bats live comfortably with viruses that can kill humans. Ask any scientist who works with them: bats aren’t symbols of an ancient evil; they’re tomorrow’s tiny health influencers. 

Those scientists aren’t just making conversation for Halloween parties: they’re using some of our most advanced technologies to work out bats’ secrets. From there, they think we might be able to develop bat-mimicking medicines that keep people healthy, too.  

What makes bats so special?

“The nitty-gritty law of nature is that small things live fast and die young,” says bat expert Professor Emma Teeling, Full Professor of Zoology at University College Dublin. “Bats buck that trend.” 

We do too, in a way. It’s not that we’re small, but, when you adjust for body size, there are only 19 species of mammal that live longer than humans. 18 of those are bats.  

“The longest-lived bat we know about lived in the wild for over 41 years, with no signs of ageing,” says Teeling, “which is like a human living to 250.” 

That bat was still flying – not just old: healthy.  

That’s important. If we want to understand all of bats’ unique adaptations, flight’s the best place to start. 

When Teeling says small things live fast, she means they burn energy quickly: that they have a high metabolic rate. One of the main theories of ageing connects this to lifespan, which helps explain why animals like mice usually die within a couple of years.  

But bats live faster than any other mammal. Flying is the hardest way to get around, and it means bats use 3 to 5 times more energy moving than mice do. If anything, then, bats’ lives should be shorter.  

“Flying causes a whole bunch of these byproducts of metabolism that break up DNA,” explains Teeling. “Broken DNA can drive cancer; it overexcites your immune system, which can make you ill; it drives all ageing. Our hypothesis is that bats must have evolved special mechanisms to allow them to deal with the damage of flight.” 

Perhaps, once you’ve worked out a safe way of swimming through the sky, the rest of living comes a little bit easier. 

Studying bats

Just look at us. People only started flying 120 years ago, but average life expectancy around the world has more than doubled since then. That’s thanks to our unique adaptations: our big brains and ability to think, which have given us vaccines and cancer immunotherapies alongside air travel. Now we can use them to learn from other animals.

“When you look to nature, you can find solutions,” explains Teeling. “After billions of years of evolution on this planet, every species alive today has a signature of survival, so the answers we need are already here. But to really understand evolution, you’ve got to look at the raw material evolution acts on. That’s the genome.” 

The genome is the complete set of DNA instructions for every living thing. It appears in full in the nucleus of every cell, where it’s wound tightly into structures called chromosomes. The fact we can now look at it is down to another one of humanity’s greatest technological achievements: whole genome sequencing (WGS).

Teeling is also a co-founding director of the Bat1K project, which aims to record the genome of every species of bat in the world. That’s a long-term goal, but the number of bat genomes sequenced is climbing, and smaller studies of single bat genomes have already taught us a lot about where their superpowers come from. 

How do bats resist cancer?

For more than a decade, Teeling’s team have been following a colony of long-lived mouse-eared bats (which have been recorded at 37 years old) in France. With the help of the local community and a conservation charity, they microchipped the whole colony, which means they can keep track of different individuals over time. 

Now, every year, the team come back to the old churches where the bats roost, to take a few drops of their blood. 

“It’s quite vampire-esque,” says Teeling, though she stresses that the process doesn’t hurt the bats. “We take blood from bats in Gothic churches back to our lab in Ireland and sequence it to see if it shows any of the changes that underlie ageing and can cause cancer in humans.” 

They’ve found the opposite.  

At the end of chromosomes are protective caps called telomeres, which, like the plastic tips on shoelaces, keep our genes from tangling or unravelling. These wear down as our cells age and divide, until, eventually, there’s so little telomere left the process can’t continue. The cell either retires from the copying life, or it dies. Cells pick up more potentially dangerous mutations as they get older, so this mechanism helps keep us healthy.

But, in 2018, Teeling’s team showed that the telomeres in mouse-eared bat cells don’t degrade. The telomeres in most cancer cells don’t either, which is how they can keep growing and dividing when they shouldn’t. They’re like zombies, relentlessly moving forward even as their bones snap and their limbs fall off.

Or, if you prefer, cancer cells are vampires. Like Dracula, they live many lifetimes, seeming normal to the rest of the body even while they’re putting it in danger. Then, as cancer cells grow into tumours, they can encourage the growth of their own blood vessels to get the energy they need. And they’re only vulnerable to certain things, like chemotherapy, radiotherapy or – for vampires specifically – a stake in the heart.  

But mouse-eared bat cells know how to look after themselves. In 2019, Teeling and her colleagues showed how they stay young, strong and under control. 

“These bats have extra checkpoints to help maintain control of how their cells divide,” she explains. Rather than stopping dividing after a certain point, they’re more careful about every division. “Then the genes responsible for repairing DNA get more active as they age; and their ability to remove other damage from their cells also increases. They clean up messes that could lead to cancer, rather than allowing damage to build up.” 

The Batman immune response

Different bats seem to have their own approaches. Horseshoe bats – which can also live for more than 30 years – regrow their telomeres while they’re hibernating. That might be even more impressive. These bats can reverse the effects of ageing on their cells. 

They do it by activating an enzyme called telomerase, which hasn’t been found in mouse-eared bats, but is also how cancer cells keep themselves going. The big difference is that bats can always press both on-switches and off-switches. It’s part of the balance that keeps them in the air. 

You can see it in the way their immune systems work, too. Ours respond to viruses with inflammation, setting up a big police cordon and leading to the pain, heat and swelling we experience when we’re ill. If things were the same in bats, their immune systems would constantly be fighting against the effects flight has on their cells and DNA, leading to the sort of chronic inflammation that can also cause cancer. Gravity wouldn’t just pull them down; it would make them sick. 

We’ve seen what that might look like. Sometimes, our bodies can seriously overreact to infections, releasing so many cytokines – proteins that promote inflammation and cell-killing processes – that our immune systems turn against healthy cells, with potentially life-threatening consequences. Cytokine storms like these are responsible for many of the deaths caused by COVID-19. The virus that causes it, SARS-CoV-2, likely came from a bat. 

For bats, though, SARS-CoV-2 has probably never been much of a problem.  

Over millions of years of evolution, they seem to have calmed their inflammatory response to infections. Instead, they coexist with viruses without experiencing any reactions. And, if those viruses become threatening, their genes catalyse a more specific antiviral response. As Dr Armin Scheben, lead author of another recent study into bat genomes, puts it: they get Batman to deal with the problem, rather than the entire police force. With him taking care of things, bats can fly long distances and snuggle up in huge colonies without spreading illnesses.

“They have an entirely different selection of immune genes,” adds Teeling. “And it gives them a perfect Goldilocks response. There’s enough of the antiviral genes to be able to control the viruses, but also a strong anti-inflammatory response to keep the immune system under control. And, potentially, they’re also using this exquisite innate immune system to remove cancer cells before they can grow.” 

From the cave to the clinic

Bat-inspired medicines won’t flip us upside-down, but they could help us achieve some of the cellular control that makes bats’ unique lives possible.  

“We want to know how the bats regulate these differences,” says Teeling. “We’re finding that they make these different switches to control gene expression, and there might even be master regulators that the bats are using to prevent ageing and cancer. If we find those, maybe we could use them.” 

And we could bring some of bats’ inner balance to the rest of our lives, too. Unusual creatures deserve our care and attention, not our fear and hate.  

In fact, as different as we seem, bats and humans have a lot in common. We might not have wings, but see those bits of webbing between your fingers? Those, stretched out, are what bats use to fly. 

Tim