Here at SciShow, we know how to stay on top of the truth.
So when there are misconceptions about science -- especially ones that seem plausible -- we
try to help clear things up.
And one topic that generates a lot of myths is … cancer.
We’re not talking conspiracy theories here -- we’re going to focus on things that sound
like they could be true, and talk about why they aren’t.
Things like: Do sharks get cancer? If you have cancer, is it okay to eat sugar? What
about superfoods? And are cancer rates rising so fast that we’re all going to get it?
A lot of these misconceptions have a tiny bit of real science at the core -- they’ve
just been misinterpreted.
Studies done in the 70’s sparked interest and created the myths that sharks don’t
get cancer, and taking shark cartilage supplements will cure or prevent cancer.
One study, by researchers at Johns Hopkins, found that certain chemicals in cartilage
-- that squishy white connective tissue -- could prevent blood vessels from forming.
Cancer researchers are super interested in targeting this process, called angiogenesis,
because tumors need a supply of blood. Cut off the blood supply and you could theoretically
starve the tumor.
Around the same time, researchers in another study fed sharks a nasty, normally cancer-causing
chemical called aflatoxin B1, waited a while, and didn’t see any tumors.
But just because you don’t see something happen one time doesn’t mean it won’t
happen ever, and if the researchers had waited longer the sharks probably would have developed cancer.
But since sharks have skeletons that are basically made of cartilage, shysters saw their chance
and started selling supplements made from shark cartilage.
Some people figure that if shark cartilage contains some chemical that prevents blood
vessel formation, that chemical should also be in supplements made from shark cartilage.
There are a few problems with this. First, life isn’t a video game. You can’t just
eat something to gain its power! No matter how much Star Wars mac and cheese you eat,
you won’t turn into a Jedi.
It doesn’t make any sense that just eating tissue from an animal that doesn’t get cancer
would pass that benefit on to you.
It’s true that cancer doesn’t tend to invade cartilage, and some of the chemicals
responsible for that effect are being tested as cancer drugs. But those can be made artificially.
Anyway, there’s definitely not enough of those active ingredients in bulk shark cartilage
supplements to have any benefit. Multiple studies have shown that.
Also: sharks DO get cancer! In the years since those earlier studies, scientists have found
sharks in the wild with tumors.
They’re not necessarily easy to find -- for one thing, sharks with cancer probably don’t
live long enough for researchers to bump into them. So if sharks do get cancer less often
than other animals, we might have a hard time finding out for sure.
But it definitely happens.
Here’s another thing people sometimes tell cancer patients about their diets: If you
have cancer, the misconception goes, you should avoid eating sugar.
The advice might be well-intentioned, but it’s also wrong -- and based on misinterpreted science.
The idea is that cancer cells really like making energy in a way that requires a lot of sugar.
Most of the time, whenever there’s oxygen around, healthy cells use that oxygen to convert
glucose sugar into energy.
It’s efficient enough that most of the energy from the sugar is converted into a form the
cell can use.
If there isn’t enough oxygen, cells can use a different process to get some energy
from sugar -- but not nearly as much.
It’s wasteful, and it’s usually not the cell’s first choice … unless it’s a cancer cell.
In 1924, a German scientist named Otto Warburg noticed that cancer cells will go for option
B even if they don’t have to. Which means that they need a lot more glucose to make
the same amount of energy.
We’re still not exactly sure why this benefits the cancer cells, but it might help them grow
even when the body tells them not to.
From this, people seem to conclude that since cancer likes sugar, you shouldn’t eat sugar.
That’s not such a far-fetched idea, and at least one or two studies have tried it,
but … not eating sugar doesn’t actually seem to give cancer cells access to less glucose.
Here’s the thing: To your body, a calorie from sugar is more or less indistinguishable
from a calorie from protein. No matter what you eat, your body is eventually going to
convert it into glucose.
So restricting the sugar you eat isn’t going to do much to affect a tumor -- it’ll get
the sugar anyway.
Those same well-intentioned diet nannies who tell you not to eat sugar will also say that
taking a ton of antioxidants will prevent cancer.
If you believe the people who market green tea and acai berries, antioxidants are the
cure for what ails us, no matter what it is. They’ll slow down aging in our cells and
prevent them from turning cancerous.
And, don’t get me wrong. Antioxidants are important. Sometimes, destructive chemicals
called reactive oxygen species get loose in our cells. They damage crucial cellular machinery,
including DNA. And … DNA damage can lead to cancer.
Antioxidants neutralize those reactive oxygen species before they have the chance to do
any harm, which is very nice of them!
So you’d figure eating lots of them would help prevent more damage.
But, like with sugar, just because something sounds like it makes sense doesn’t mean
it actually does -- that’s why scientists do studies to look for evidence.
And there isn’t much evidence that taking antioxidant supplements lowers the risk of cancer.
It’s not for lack of trying. A bunch of major clinical studies have followed people
taking antioxidant supplements like vitamins A and E and found very little benefit.
It is still possible that certain kinds of antioxidants might work -- these studies concentrated
on purified supplements, and there’s a chance those antioxidants could be better for you
when they’re still in food form. Scientists can’t say for sure yet.
But antioxidants are still good for you, right? Might as well load up on them anyway--it can’t hurt.
Actually, if you already have cancer, it might hurt.
According to some studies, antioxidant supplements might actually speed up the progression of cancer.
For example, one recent study by Swedish researchers found that melanoma -- a type of skin cancer
-- spread more aggressively in mice that received antioxidant supplements than in mice that didn’t.
The reason seems to be that antioxidants can’t tell the difference between healthy cells
and cancer cells, and will do their jobs everywhere. That leads to stronger, healthier cancer cells, too.
In fact, those researchers think antioxidants might even enhance a cell’s ability to travel
around the body. Which, when it comes to cancer, is very, very bad -- that’s how it spreads.
Speaking of things that are supposed to be good but might help cancer spread instead,
let’s talk about biopsies.
When doctors want to know if certain types of tumors are dangerous, they sometimes use
a needle to extract a tiny piece it.
It’s a useful procedure, because it lets doctors tell not only IF a tumor is cancerous,
but how advanced it is.
But some people worry that biopsies come with an element of risk.
If doctors are plunging needles into tumors, won’t that dislodge the tumor cells and
help them to spread?
Again, it sounds pretty reasonable. One study of several hundred breast cancer patients
showed that about 30% of the time, biopsies did shake loose bits of tumor.
Sounds scary--but there’s a catch.
How long the researchers waited before checking back made a huge difference to how many displaced
tumor chunks they found. The longer they waited, the fewer rogue tumor cells there were.
Which means that even though bits of tumor got loose, after a while they just...died.
When biopsies free tumor cells, those cells aren’t usually designed for spreading and
making more tumors.
There are also techniques doctors can use to minimize the spreading of tumor cells,
like biopsy needles that include tiny vacuums.
Overall, the risk of a tumor spreading as a result of a biopsy is incredibly small,
especially compared to how much information doctors can get from those biopsies.
There are some exceptions, though.
Testicular cancer actually does have a decent chance of spreading after a biopsy -- which
is why doctors generally don’t do biopsies on testicular cancer.
If they think someone has a tumor, they’re more likely to just remove the whole testicle.
Now let’s talk about two misconceptions when it comes to the current state of cancer
in the world. The first is the idea that cancer is a modern disease.
It might sometimes seem like that’s the case, because modern life is full of potentially
cancer-causing stuff, and we hear about them all the time.
For instance, certain kinds of industrial pollution and environmental contaminants can
lead to cancer.
And easy access to fatty, sugary, nutritionally deficient foods contributes to obesity, which
can also lead to cancer.
Plus … tobacco.
But even if we all returned to some pre-Industrial Revolution pastoral lifestyle, cancer wouldn't
just vanish.
Lots of things that cause cancer have been around as long as the human race, or longer.
Things like ultraviolet radiation, wood smoke, and genetics can all cause cancer, and they
have nothing to do with our modern way of life.
Cancer has been found in three thousand-year-old human remains. Even dinosaurs had tumors.
The disease is way older than we are.
Which leads us to a closely related myth: Cancer is killing more people around the world.
You might see kind of scary headlines, talking about how more people are getting and dying
from cancer.
Others will say that those headlines are lying and we’re all going to be fine.
But, like so many things in life, the truth is … complicated.
There are a lot of factors here. For one thing, the global burden of cancer--that’s the
total amount of cancer in the world-- is shifting from developed to developing nations.
Meaning, in higher-income nations, rates of cancer are mostly shrinking. But they’re
rising in others.
Secondly, death rates from cancer in the United States are declining. We’re getting better
at both prevention and treatment, so you’re less likely to get cancer and more likely
to get better if you do.
That said, the total amount of cancer cases and deaths is going up.
That’s because, even though we’re getting better at stopping cancer, and percentage-wise
it’s decreasing … we’re living longer.
Our standard of living has improved, so there are more older people on the planet. People
don’t die of childbirth or malnutrition as much as our ancestors did.
But the older someone gets, the higher their risk of cancer -- their body simply has more
time to develop it.
And because the population of old people is getting bigger, lots of those people will
get and die from cancer.
Basically, we’re winning the fight against cancer, but we’re also winning other fights
that mean people live long enough…to get cancer.
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