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While cancer is a terrible disease, some things you've read about it might not exactly be true. In this episode, we'll be debunking these 6 common myths about cancer—join host Hank Green for a new episode of SciShow!

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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 myth is cancer. We're not talking about conspiracy theories here, we're gonna 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 going up so fast that we're all going to get it?"

All of these misconceptions have a tiny bit of real science at the core, they're just been misinterpreted.

Studies done in the 70s sparked interest and created the myth 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. And 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 figured that if shark cartilage contains some chemical that prevents blood vessel formation, that chemical should also be in supplements made from shark cartilage.

There's a few problems with this. First, life isn't a video game... you can't just go eat something to gain its power. No matter how many Star Wars mac and cheese you eat, you're not going to turn into a Jedi. It doesn't make any sense that just eating tissue from another 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 early 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 may 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 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 sure why exactly 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 actually such a far-fetched idea and at least one or two studies have tried to test it out, 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 the tumor; it'll get the sugar anyway.

Though 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 teas and açaí 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 because sometimes distractive 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 real 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 look for evidence, and there isn't much evidence that antioxidant supplements lowers the risk of cancer. And 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 that 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? You might as well load up on them anyway, it can't hurt.

Well, 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 from researchers in Sweden found that melanoma, a type of skin cancer, spread more aggressively in mice that received antioxidant supplements that 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 thing that antioxidants may 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 cancers 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 of 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 spread?

Again, that's 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, these 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 very tiny vacuums.

Overall, the risk of a tumor spreading as the 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 food contributes to obesity, which can also lead to cancer. Plus, you know, tobacco.

But even if we return to some pre-industrial revolution pastoral lifestyle, cancer wouldn't just vanish. Lots of things that cause cancer have been around for as long as the human race or longer. Things like ultraviolet radiation and 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 3,000 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 some kinda scary headlines talking about how more people are getting and dying from cancer. And others will say that those headlines are lying and that we're all gonna 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 nations to developing nations, meaning in higher income nations, rates of cancer are mostly shrinking. But they're rising elsewhere.

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 people on the planet. People don't die in childbirth or of 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 lots of other fights that mean people get to live long enough... to get cancer.

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