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Comment by metafunctor | Hacker News Reader

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

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

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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.

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

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.

Interesting question. I suppose so. I know identical twins can typically receive organ transplants from each other with complications. So theoretically they should be able to receive tumor transplants (which is what clonal transmissible cancer is).

I wouldn't be so sure, a cancer that doesn't express classical MHC but still manages to suppress NK cells has a chance. It would probably have to master a few other immunosuppressive pathways but it's not beyond imagination.

Transplanted HeLa cells were shown to engraft in unrelated human "subjects" (in some truly evil experiments by https://en.wikipedia.org/wiki/Chester_M._Southam), other cell lines probably have the same capacity.

So if you have a population of humans who, for generations, have selected genes via inbreeding, would it be a thing to have transmissible cancer?

I'm thinking of the Amish population near my hometown that has definite inbreeding traits and particular disabilities associated with inbreeding in their bloodline/families.

Would it be possible for them to develop some kind of transmissible cancer?

Human cancers aren't contagious, at least not the way the cancer in the article is. Some risk factors for cancer, like HPV, are contagious in humans, but those aren't cancers themselves.

The "lie" (which was not a lie at all) that you were told actually meant that you can't get cancer from being around someone with cancer. That's still true.

It's largely true, and teaching it that way to school kids is important so they don't avoid friends/family who may have cancer of some sort. My son's friend has cancer and it was one of his first questions - "can I catch it?"

The rare human cancers that are transmissible like cervical cancer get covered in sex-ed, and interventions like condoms are effective.

> The rare human cancers that are transmissible like cervical cancer get covered in sex-ed

Even cervical cancer isn't transmissible, just the HPV risk factor

Hopefully grade school children are not at risk of ctvt

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