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Comment by idiocache | Hacker News Reader

“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?

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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.

Particular carcinogens absolutely do cause particular mutations or at least mutational patterns. Lookup mutational signatures. Signature 4 for smoking for example

The most obvious way is that carcinogens affect parts of the body differently. Iodine collects in the thyroid, some compounds accumulate in the gut, alpha and beta affects the outer layers of the body.

Epigenetics can cause different parts of DNA to be more or less exposed in different parts of the body. There are also indirect effects from chemicals- some carcinogens can cause changes in proteins, or be bound to proteins, which can cause them to be around certain regions of DNA more.

Mostly though you see that kind of thing more in viral/bacterial cancers- a sizeable percentage of all tumors are caused this way.

I didn't read the article properly, obviously. Thanks for the responses.

The article suggests that mutation patterns arise in predictable ways depending on the carcinogen, which is how they pinpointed the origin of CTVT to China.

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