
CTVT – A contagious cancer that spreads from dog to dog - andyjpb
https://www.theatlantic.com/science/archive/2019/08/ctvt-tumor-broke-all-rules/595246/
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nso
This is widespread with street dogs (and "street" dogs) where I live in
Mexico. It can get pretty nasty.

Female dogs will typically get tumor growths on the vagina, and at its worst
will look like someone took a meat grinder to her parts. It will blow up in
size and at some point the dog will succumb and die.

The male dog will get it in the penis, and typically will be caught sooner as
bloody discharge from a male dog is something that raises a red flag quicker.

My mother-in-law has had 3 dogs get infected at different points in time, one
female that had to be put down and two male that recovered.

~~~
jjtheblunt
That's sad, because it's trivially curable, supposedly. Man, if they'd snip
those male dogs' with a vasectomy, what an improvement it would be...same here
north of the mexico-us border.

~~~
asdfman123
Can't you just avoid this if you spay and neuter dogs?

~~~
nso
Sure, but who pays for spaying and neutering the plethora of street dogs in
the poorest states in Mexico? And many people have dogs without the means of
paying for this (or any) kind of surgery.

Between us and my MIL we have 10 dogs, and all of them except one are fixed.
I've made sure of that. I'm not able to win the argument over the last one,
but it's old now anyways. The dogs she had that got sick was from before I was
in the picture.

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throwaway5752
Three weeks ago:
[https://news.ycombinator.com/item?id=20590682](https://news.ycombinator.com/item?id=20590682)
and
[https://news.ycombinator.com/item?id=20593109](https://news.ycombinator.com/item?id=20593109).

One year ago:
[https://news.ycombinator.com/item?id=17489382](https://news.ycombinator.com/item?id=17489382).

5 years ago:
[https://news.ycombinator.com/item?id=7118621](https://news.ycombinator.com/item?id=7118621).

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iskander
Coolest finding in the paper:

"Our analyses reveal a mutational signature, signature A, that occurred in the
past but ceased to be active from about 1000 years ago. A recent study (37)
detected evidence for an excess of C>T mutations at TCC contexts, the mutation
type most prevalent in signature A, accumulating in the human germ line
between 15,000 and 2000 years ago. If this human mutation pulse is due to
signature A, it could indicate a shared environmental exposure that was once
widespread but has now disappeared."

There will now be a small academic race to identify this mysterious carcinogen
which both humans and this dog cancer were previously exposed to.

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Reason077
See also DFTD, which affects Tasmanian Devils:

[https://en.wikipedia.org/wiki/Devil_facial_tumour_disease](https://en.wikipedia.org/wiki/Devil_facial_tumour_disease)

~~~
cmroanirgo
Thanks. I was wondering if there was a correlation

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JorgeGT
The actual paper:
[http://doi.org/10.1126/science.aau9923](http://doi.org/10.1126/science.aau9923)

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metafunctor
I was told in grade school that cancer is not contagious... well, turns out
that was just lies to children. [1]

This reminded me of the Radiolab episode “Devil Tumors” [2], featuring a
similar kind of contagious cancer in Tasmanian Devils.

[1] [https://en.wikipedia.org/wiki/Lie-to-
children](https://en.wikipedia.org/wiki/Lie-to-children)

[2] [http://radiolab.cs.odu.edu/radiolab-devil-
tumors.html](http://radiolab.cs.odu.edu/radiolab-devil-tumors.html)

~~~
dcolkitt
Clonally transmissible cancers are typically only seen in highly inbred
populations. Tasmanian devils qualify because they went through a population
bottleneck when they first colonized the island. Dogs qualify because of human
breeding. (It's pretty unlikely that CTVT could be transferred to a wolf, even
though pet dogs and wolves are the same species.)

The reason most cancers aren't transferrable, is the same reason that organ
transplants are so hard. Most individuals in most species have unique antigen
profiles. The immune system attacks any foreign bodies without matching
antigens. An internally generated tumor works because it's cloned from an
individual's own cells.

But a foreign tumor, is very unlikely to have a matching antigen profile.
Therefore the immune system will attack and destroy with extreme prejudice.
However a highly inbred population may lack the sufficient genetic diversity
to have individually unique antigen profiles. In the extreme case if we were
all clones we could pass tumors back and forth with ease.

The short answer is that it would be virtually impossible to see any
widespread cases of clonally transmissible cancers in non-immunocompromised
humans.

~~~
weinzierl
So does that mean that cancer is contagious among identical twins?

~~~
moftz
I suppose it depends on their individual immune systems. If they didn't live
in close contact, they may not share the same immune system. One may have a
weaker immune system than the other making it possible for the cancer to
spread easily one way but not the other.

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burtonator
mutation, replication, natural selection. This is all you need for evolution.
So evolutionary cancers makes sense once you add transmission.

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idiocache
“It’s very mysterious,” Murchison says. “This cancer was exposed to something
that caused this very particular mutation, and has never been seen in any
human cancer ever, and that seems to have stopped 2,000 years ago. We don’t
know what that carcinogen is, and we’d love to. I guess it was probably
something in the dogs’ environment? This is a very crazy idea and we don’t
really believe it, but maybe ancient people who owned the dogs tried to treat
[their tumors] with some kind of chemical?”

This feels wrong - surely particular carcinogens don't cause particular
mutations. Isn't this just chance?

~~~
ppseafield
The article states that different carcinogens do cause particular styles of
mutation.

> Many carcinogens mutate DNA in distinctive ways: Sunlight, for example,
> creates a very different pattern of mutations than cigarette smoke.
> Murchison’s team found that CTVT contains a lot of those sunlight
> signatures, especially at lower latitudes, where the sun is stronger. For
> example, CTVT in Mauritius has more sunlight-induced mutations than the same
> tumor in Russia.

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jcims
This seems to stretch the definition of cancer. The tumors do not share DNA
with the host, it's more like a bacterial infection or parasite.

~~~
ceejayoz
That's largely the point of the article, isn't it? That it's arguably its own
species?

> “CTVT is like its own organism,” Murchison says. “It isn’t really a dog. Is
> it a cancer, still?”

~~~
jcims
Missed that, thank you.

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thrownaway954
I send my dog to day care all the time. now I'm thankful that they require
yearly shots and full examinations.

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mbrumlow
So if dogs have a caner that spreads deom dog to dog...

Do humans have anything like that? If we did would this not cause a panic?

~~~
CodeCube
Without having read the article, and not being a biologist ... is this
anything like HPV/Cervical cancer for humans?

~~~
3JPLW
The third paragraph:

> To clarify, several cancers can be caused by infectious entities; cervical
> cancer, for example, is the work of HPV, a sexually transmitted virus. But
> in those cases, the cancer itself is not infectious and cannot spread. CTVT
> is different: Each cancer cell is a free-living parasite that can set up
> another tumor on another dog.

Put another way, HPV is a virus whose effects can cause cancer. That is, it
causes mutations in _your own_ cells that cause them to become cancerous.

CTVT is essentially a parasitic cell line — not your cells hopping a ride on
you.

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privexpert5
Is anyone else terrified by this?

~~~
ceejayoz
A six thousand year old cancer? Why?

~~~
sdinsn
What does the age of the cancer have to do with this?

~~~
ceejayoz
We've coexisted with it safely for six millennia. As such, it seems odd to be
terrified of it.

~~~
sdinsn
SIV appeared somewhere between 1000 and 20000 years ago. Then ~100 years ago,
it mutated to HIV and shortly after infected humans. We never know what could
happen.

~~~
ceejayoz
By that logic, we should be terrified of _everything_.

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asdfman123
> Its future is uncertain, though. While failing to acquire beneficial
> mutations, CTVT is also failing to weed out harmful ones. That’s
> understandable, because much of its DNA comprises genes for building a dog.
> It can afford to let those mutate into obsolescence. But over time, the
> genes that it still needs will also take hits. Slowly, the tumor will become
> weaker and less efficient.

I wonder if there's an analogy to governments and laws. As our laws become
more complex and "mutate," governments gradually become less effective.

