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Why 90-Year-Olds Get Less Cancer
Why 90-Year-Olds Get Less Cancer
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Subtítulos (203)
0:00
When you think about getting older, charming side effects like sore joints,
0:03
wrinkles, or a toothless smile might come to mind.
0:06
And while there are maybe some things to look forward to,
0:08
like that AARP membership, it might not seem to balance out entirely.
0:13
There may be one other advantage, however.
0:15
At a certain point of aging, our risk of cancer starts going down.
0:20
And if you’re getting hung up on the idea that cancer is an old folks’ disease, I mean, kinda.
0:24
But keep watching.
0:25
Because just like with all things in cancer, it is not that simple.
0:29
[♪ INTRO]
0:32
So cancer is one of those diseases that can strike anyone, regardless of age,
0:36
though it tends to be more likely in older folks.
0:39
And there are a lot of things that can affect the risk of different cancers.
0:42
We know that a lot of cancer risk can be affected by genetic factors,
0:45
such as certain variants of the BRCA1 gene increasing the risk of breast cancer.
0:50
That’s why they call it brack-uh, B-R-C-A.
0:52
It stands for BReast CAncer
0:54
Environmental factors can also play a role, like smoking for lung cancer.
0:58
But so can plain dumb chance.
1:00
You can have no genetic risks and avoid things like smoking
1:04
and too much sunlight, and still develop cancer.
1:06
And that’s because as your cells divide,
1:08
which they’re doing all the time, they can make some mistakes.
1:11
A lot of those mistakes are harmless.
1:13
Maybe one DNA letter changed but in a place where it didn’t make any difference,
1:17
or maybe that mutation caused the cell to die, so it didn’t start mass producing the mistake.
1:22
But the more your cells divide, over the course of a few decades,
1:25
the more likely it is to get one of the bad mutations,
1:28
or to accumulate enough mutations where you start showing symptoms of a disease.
1:32
That’s a big part of why cancer is generally more likely as you age.
1:36
Plus, you have more time to be exposed to environmental risk factors,
1:39
your immune system usually weakens, and your body isn’t as good at repairing DNA.
1:44
All of that spells more cancer for old people.
1:47
So it makes sense that when you look at cancer incidence, it pretty much increases with age.
1:52
…Until you get to the very oldest people.
1:55
At some point, it looks like cancer incidence starts to actually go back down.
2:00
A paper from 2017 found that this happened in the “oldest-old” group,
2:04
which is anyone 85 years or older.
2:06
That’s a little strange because, theoretically, that group has had the most time to hoard those
2:11
random mutations, rub shoulders with carcinogens like tobacco or the sun,
2:15
and power down their immune systems from regular ol’ aging.
2:18
With all those factors working in favor of tumor development,
2:21
some researchers aren’t convinced that the cancer decline is legit.
2:25
It might be the incidence only looks like it goes
2:28
down because it isn’t being detected in that age group.
2:31
There are some good reasons why that could be happening.
2:34
Detecting cancer isn’t always the most comfortable experience.
2:37
At 95, a colonoscopy might not feel like it’s worth the trouble,
2:41
especially with how grueling the prep can be.
2:43
Though if you are under 95,
2:45
I am here to tell you that colonoscopies aren’t as bad as they’re made out to be.
2:48
If your doctor says do it, please do it.
2:50
Additionally, if an individual is too frail or has chronic conditions,
2:53
they might not be a candidate for certain procedures.
2:56
And if the procedure requires anesthesia,
2:58
the medical team may have to consider the risks and benefits of detecting that cancer.
3:02
Plus, someone in their 90s might not care to know whether they have cancer or not,
3:07
because they are adamant about not doing intensive treatments like chemo or surgery.
3:12
At that stage of life, you might want to consider quality over quantity.
3:16
It could also be that the individuals prone to cancer already got it and succumbed to
3:20
it earlier in life, leaving most of the oldest-old cancer-free.
3:24
A kind of natural selection bias.
3:27
But even though those things could affect how we understand cancer incidence in old folks,
3:31
the consensus among epidemiologists today
3:33
is that the decreased incidence of cancer among the oldest-old is real.
3:38
So researchers out of Stanford and UPenn asked, what gives?
3:42
And their 2025 paper suggests that there might be something
3:46
on the molecular level working to older folks' advantage when it comes to cancer.
3:51
But before we get to that, we need to keep the lights on with this quick break.
3:55
If you made it this far, you’re probably the kind of person who
3:58
loves engaging with new ideas and learning outside of a classroom.
4:02
That’s what we offer at SciShow, and it’s what Brilliant offers too!
4:06
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4:09
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4:15
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4:18
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4:36
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4:41
which gives you unlimited daily access to everything on Brilliant.
4:47
The researchers started where a lot of researchers do: with a bunch of mice.
4:52
They split the mice into two groups, young and old,
4:54
which translated to spry 5 month old mice versus geriatric mice closer to 21 months old.
5:01
The oldest old mice!
5:03
Then they used gene editing to give both groups of mice lung cancer.
5:07
For anyone who isn’t a molecular biologist, that means identifying a gene that,
5:11
when changed just a smidgen, can pretty much guarantee cancer will develop by
5:15
doing things like eliminating all the cellular division checks and balances.
5:19
It’s like a company suddenly fired their entire quality control team.
5:22
Something would probably go really wrong, really quickly.
5:25
Genes that can easily cause tumor-inducing disaster with
5:29
just a tiny change are called oncogenes.
5:31
And the oncogene these scientists messed with was KRAS, whose mutations are one of the most
5:36
common linked to any cancer involving a solid tumor, including lung cancer.
5:40
So they took that cancer prone version of KRAS,
5:43
and put it in a virus, and then they delivered the virus into the mice’s
5:46
lungs so that it would spread the mutated gene to their lung cells and induce a lung tumor.
5:52
Inducing the cancer was important so that everyone was on a level playing field.
5:56
Rather than having the elderly mice having a cancer built on a lifetime's
5:59
worth of mutations and the youngins’ cancer caused by just one very unfortunate mutation,
6:04
inducing the tumors made everyone start with genetically identical cancer.
6:08
But that cancer did not stay identical for long, because after giving the cancer 15
6:13
weeks to do its thing, the young mice had worse tumors than the older mice.
6:18
Specifically, the aged mice had 2 to 3 times fewer tumor growths than the young mice,
6:23
and four to five times fewer cancerous cells in general.
6:26
And the size of the tumors was noticeably different too,
6:29
with the older mice having significantly smaller tumors than the younger mice.
6:33
Fewer tumors means some of the cancer was prevented from even starting,
6:37
while the smaller tumors means their growth was also inhibited.
6:40
It’s as if the older mice had some sort of beneficial effect that was
6:44
basically weeding and pruning their cancer.
6:47
At first, researchers thought that maybe the virus
6:50
didn’t get into the cells of the older mice as well as it did the young mice.
6:53
So being very clever scientists, they added a glowing marker to the virus,
6:57
injected it into the mice again, and played spot the difference between the old and the young mice.
7:02
Except it wasn’t a very good game,
7:04
because the glowiness in the tissues among both groups was pretty much the same.
7:07
That means the virus, with its cancer-happy version of the KRAS, was getting into the cells
7:13
equally as well, but something else was limiting the subsequent cancer development and growth.
7:18
The next idea was that there might be a tumor suppressor gene working
7:21
better in the older mice than in the younger mice.
7:23
A tumor suppressor being the opposite of an oncogene – a gene that protects cells from cancer.
7:29
And that would make sense, but the researchers found the opposite was true.
7:32
One of the ways a mutated KRAS gene can cause tumors is by activating the PI3K–AKT pathway.
7:39
We’re getting deep in the weed now, everybody!
7:41
This is a specific signaling pathway, which is a cascade of little chemical
7:45
messages between molecules that trigger functions in a cell.
7:49
This specific pathway tells cells to divide and not die,
7:52
which is why it plays a big role in tumor development.
7:55
And that is where tumor suppressor genes come in, because leaving that
7:58
pathway unchecked would be bad news for people who prefer to not have cancer.
8:02
The scientists looked at a bunch of tumor suppressor genes,
8:04
but the one that really caught their eye was the PTEN gene.
8:07
That gene is really good at slowing down the PI3K-AKT pathway.
8:11
The idea was that if aged mice have smaller and fewer tumors,
8:15
then this gene was probably working overtime to make that happen.
8:19
And they did see a difference in how effective
8:21
the tumor suppressor genes were in old mice versus young mice.
8:25
Except, not in the direction they expected.
8:27
When they knocked out the PTEN gene, tumors in the younger group grew over two times
8:32
more than those in the older group, even though PI3K signaling increased in both.
8:37
Knocking out genes is something molecular biologists do to find
8:40
out what goes wrong when they’re missing.
8:43
So this result makes it seem like PTEN is doing more work in younger cells compared to older ones.
8:49
The effect of several other tumor suppressor genes also decreased with age.
8:53
So those lazy tumor suppressor genes weren’t to thank for the smaller tumors in older mice either,
8:59
since they were apparently more active in the younger mice.
9:03
But that experiment does suggest that something in the PI3K-AKT pathway gets
9:08
less effective with age, which might partially explain the smaller tumors.
9:13
The researchers also noticed that when they knocked out the PTEN gene in the older mice,
9:17
the cancer cells looked younger, which is weird since no PTEN should mean more
9:23
PI3K-AKT signalling, which would force cells to keep living even when they’re super old.
9:29
All of those surprising findings means the researchers did not find
9:32
the answer as to why the oldest-old have a decreased risk of cancer,
9:36
and highlights why your grandparents really deserve to be included in more research.
9:41
But those researchers aren’t the only ones who have tried to suss
9:44
out this situationship between aging and cancer.
9:47
A paper from 2003 presented some reasons why tumors might
9:51
be at a disadvantage when they target older folks.
9:54
One idea proposed is that you’re less likely to be exposed to carcinogens during your golden years.
10:01
Somewhere between 2 and 8% of cancers are caused
10:04
by exposure to carcinogens while you’re on the job.
10:06
By the time you’re 80, there’s a pretty good chance that you have retired,
10:09
so if you were being exposed to hazardous substances, you probably aren’t anymore.
10:14
And if you’re in an assisted living or nursing facility, there are probably
10:17
fewer environmental carcinogens like tobacco.
10:20
A lot of the environmental changes associated with aging could mean less
10:24
exposure to carcinogens, so a lower incidence of cancer would make sense.
10:28
But that 2003 paper clocked some physiological reasons
10:31
why the incidence might decrease with age too.
10:34
As you age, your cells slow down in a lot of ways, including the speed at which they divide.
10:40
That goes for healthy cells and unhealthy cells alike, such as tumor cells.
10:45
So for that mouse experiment, it might not be too surprising to see the older mice
10:49
with smaller tumors, because it might just take longer for their tumor cells to divide and grow.
10:55
All of the cells suck when you’re old.
10:57
But that only explains why the tumors would be smaller, not why there would be fewer of them.
11:02
And for that, the authors credit a population of cells called senescent cells.
11:06
Senescent cells are cells that are done multiplying but are not dying.
11:10
They’re essentially permanent retirees, and as you age, you build up more and more of them.
11:16
The key point is that they are done replicating, which means they can’t be compelled out of
11:21
retirement even if they’re infected with a weird pro-cancer virus gene thingie made in a lab.
11:26
Older folks have more of these cells that are essentially immune to becoming cancerous,
11:31
which could explain why the older mice had fewer tumors.
11:34
It’s important to note that those cells can also release chemicals that increase
11:38
the risk of cancer, so this isn’t a clean cut Scooby Doo mystery with a single right answer.
11:43
Took his mask off.
11:44
“It’s you, the Senescent Cells!
11:46
You’re so old!”
11:47
Both cancer biology and aging are complicated and deserve far more attention.
11:52
But as we do learn more about the relationship between aging and cancer,
11:56
this kind of research could guide more tailored treatment across the lifespan.
12:00
Like, perhaps treatments targeting PTEN would be more effective in older
12:04
folks since it seems like that gene gets a bit lazy with age.
12:08
Or maybe further research will identify a gene or pathway that really does help older
12:12
people fight off cancer better, and it can be used in treatment for younger cancer patients.
12:16
All of that starts with including more older people in cancer research,
12:20
especially since they have historically been underrepresented in those studies.
12:23
And in recent years, the FDA has even issued statements telling researchers to do as much.
12:29
Not only is that a win for science in the spirit of inclusion and learning more, but it might even
12:33
mean a few more of those golden years, if not for meemaw, then maybe someday for you.
12:41
[♪ OUTRO]
