Comments on: Contagious cancers switch their batteries

By: gcochran

gcochran — Tue, 25 Jan 2011 08:47:55 +0000

Something similar was observed in Syrian hamsters, once upon a time. Note that CTVT is not that virulent, which is not surprising, considering that there is probably a payoff in allowing long host survival. Along that line, cell line infections like this don’t have to act like a cancer at all: they could cause a chronic illness, or even be fairly harmless.

Some might practice host manipulation: they would have a good start, able (with a mutation or two) to manufacture all kinds of signaling molecules.

By: Ed Yong

Ed Yong — Sun, 23 Jan 2011 02:24:23 +0000

Casey – I had to say most to account for CTVT and the Tasmanian devil facial tumour. As far as we know, these are the only two directly contagious cancers. There aren’t any that affect humans.

By: Casey

Casey — Sat, 22 Jan 2011 19:09:09 +0000

You said “Most cancers (including those that affect humans) aren’t contagious”. Out of curiosity, are there any cancers that are directly contagious? I understand some cancers that are related to infection can be “contagious” because the virus or bacteria are contagious, but are there any analogs to CTVT in humans?

By: Ed Yong

Ed Yong — Fri, 21 Jan 2011 17:48:27 +0000

@Dunbar, Nathan and others – There’s no evidence to date of a similar thing going on in human cancers and bear in mind that these are some of the most thoroughly researched diseases around. However, when I last wrote about this, I mentioned that the best place to look for such cases would be in people with weaker immune systems including transplant patients and those with HIV.

By: Matt

Matt — Fri, 21 Jan 2011 13:14:41 +0000

This is really cool. And I love the evolutionary implications. However, aren’t our (human’s) mitochondrial DNA exceedingly similar from individual to individual? I’ve always heard the mitochondrial DNA as described as “more-ancient”. If this is true, then there was likely something very different about the earliest cells engulfed mitochondria than the cancer cells described in Ed’s post. Or, possibly, if the process/hunger for new energy was the same, there must have been a ver stable individual cell-mitochondria composite that found some sort of equilibrium point allowing the individual to develop and evolve into more complex things.

By: JGB

JGB — Fri, 21 Jan 2011 12:20:56 +0000

It’s slightly different, but in many ways the same phenomena. The human HeLa cell line derived from Henrietta Lacks, has evolved to the point of being a successful single celled organism within the last 60 years, and it now somewhat routinely is found as a contaminate in labs.

By: Trond Engen

Trond Engen — Fri, 21 Jan 2011 08:36:34 +0000

Nathan: I don’t understand how the cancer could have originated both 10,000 years and 2500 years ago.

Act of Independence: 10000 years ago.
The last common ancestor of current cells: 2500 years ago.

I.e., only one of the doubtless many branches stemming from splits between 10000 and 2500 years ago has survived.

By: Dunbar

Dunbar — Fri, 21 Jan 2011 05:37:12 +0000

To see if any cancer is contagious, I’d imagine they would apply the same epidemiological principles with regard to other infectious microbes, like identifying patient zero and such. To my mind, one human can get a cancer from another human, like if the former got a bone marrow transplant from the leukemia-afflicted latter. Of course, this doesn’t mean that the cancer is contagious because people normally don’t go around giving each other bone marrow transplants; people do, however, go about bumping uglies and/or fighting, so if ever a human transmissible cancer is found, we’d probably figure pretty quickly how it is transmitted.

The cancer originated 10 000 years ago, but the current strain infecting dogs today branched out from its cousins around 250-2500 years ago. That’s how I read the statement.

By: Nathan Myers

Nathan Myers — Fri, 21 Jan 2011 04:15:36 +0000

There’s no reason to think, is there, that none of the myriad cancers that plague humans are of this sort. Has anybody really looked? How would you go about that?

I don’t understand how the cancer could have originated both 10,000 years and 2500 years ago.

By: Dunbar

Dunbar — Thu, 20 Jan 2011 20:39:14 +0000

What would keep it from crossing over to humans is the fact that CTVT is adapted to dogs and to evading canine immune systems. If you were to graft a CTVT to a human, the most likely scenario would be an immediate rejection by your immune system. It’s the same sort of phenomenon that frustrates xeno-transplants of animal organs into humans. Also, an observation: I doubt societies that eat dogs (which doesn’t really happen that often, at least in China) would accept eating a cancer-ridden dog any more than they would eat flu-infected chickens or scrapie-infected sheep or foot-and-mouth infected cows. So the answer to your question is, no.

On HIV, it evolved from a simian virus called SIV. Since apes and such are our closest living relatives, it isn’t too hard to imagine how a virus that can infect them might be able to somewhat infect us and then successively evolve to be a human-specific pathogen by adaptation.

“Mad cow” isn’t really contagious amongst humans anyway, because it is incredibly unlikely for one human to eat another human that ate contaminated beef, at least nowadays. There have been human to human transmissions of human prions in societies that practised cannibalism (look up Kuru in Wikipedia).