Thread: Contagious Cancer

Hi guys,
a while back my sister told me about how the tasmanian devil is going extinct because they are being wiped out by a contagious cancer.
i think it is a really cool topic and an example of why genetic diversity is so important- just wanted to know what you all think or at least be thankful that our cancers aren't contagious

http://www.cnn.com/2009/WORLD/asiapc...il.threatened/

Oh, but some of them are. the HPV virus that can be sexually transmitted has a tendency to induce uterine cancer in women and penile cancer in men.

There's also one called Canine Transmissible Venereal Tumour (CTVT). Weirdly, the tumour is not related to the dog its growing on - it's more like an asexually reproducing parasite (presumably derived one single dog or ancestral species at some point way back) that gets transmitted from dog to dog. (link)

however both of the cancers you listed are cancers caused by sexual contact. the cancer that is affecting the tasmanian devils is from skin to skin contact

i really think that the Canine Transmissible Venereal Tumour (CTVT) is really interesting though. i mean, if the dna of these cells are different, one would expect that the immune system of the dog would recognize it and kill off the foreign cancer cells.

that is the difference with CTVT and the Devil facial tumour disease (DFTD). For the tasmanian devils they have so little genetic diversity that their immune system cannot recognize these cells as foreign, that is why the disease is so devastating to them.

I think you misunderstand how "contagious" cancers are passed. It's not the cancerous cells themselves. It's a retrovirus that gets passed from one animal to another, and in the process of replicating itself messes with the DNA and causes cancerous cells to be generated in the host.

The fascinating thing about both CTVT and DFTD, Paralith, is that no virus seems to be involved. The tumour cells themselves can be thought of as infectious parasites that grow on their "host" - at least in the case of CTVT (I've never heard of the Tasmania Devil cancer before). According to wikipedia (hehe) both these diseases are the only known cases of transmissible cancers that have been discovered so far.

dlambert, I don't really see the difference that you make between these two cell lineages. Infection starts by contact with different parts of the body is all, really.

HPV actually isn't a retrovirus, the predisposition to cause cancer comes from it's manipulation of the cell cycle, by pushing cell replication forward, to promote it's own reproduction. This is why some HPV strains cause those unsightly "warts".

HPV is also one of the primary causes of anal cancer.

HPV is transmitted through skin-skin contact dlambert. Almost every person on Earth is infected with more than one strain of HPV.

Although not as directly oncogenic as HPV, Hepatitis is a major cause of liver cancer. Moreover, HIV and other immune compromising viruses raise the risk of cancer by a lot. (E.g. Kaposi Sarcoma which is caused by a herpes virus, but is only able to form tumours in immune compromised individuals). Another herpes virus, Epstein-Barr virus, has been linked to lymphonas and gastric cancer.

Viruses mess with cell replication, so it is understandable that many may be oncogenic.

Originally Posted by Zwirko

The fascinating thing about both CTVT and DFTD, Paralith, is that no virus seems to be involved. The tumour cells themselves can be thought of as infectious parasites that grow on their "host"

I'm amazed that allogeneic cells passed on from a different animal wouldn't be recognised and destroyed by the host's immune system.

The problem with 'normal' cancers, is that the cells are from your own body and the immune response is not sufficient to control the tumours. But the antigens expressed by a different animal's tumour would be different, and highly immunogenic, I would think.

Originally Posted by Zwirko

dlambert, I don't really see the difference that you make between these two cell lineages. Infection starts by contact with different parts of the body is all, really.

I suppose you are right on that, contact is contact no matter through whatever method.

Originally Posted by mascot

I'm amazed that allogeneic cells passed on from a different animal wouldn't be recognised and destroyed by the host's immune system.

The problem with 'normal' cancers, is that the cells are from your own body and the immune response is not sufficient to control the tumours. But the antigens expressed by a different animal's tumour would be different, and highly immunogenic, I would think.

that is completely true, that is why DFTD is so interesting. because the gene pool is so small for the tasmanian devil population, the immune systems of these animals are having difficulty identifying self from foreign, which is why this disease is so devastating for their population. this really shows the importance of genetic diversity

Originally Posted by mascot

I'm amazed that allogeneic cells passed on from a different animal wouldn't be recognised and destroyed by the host's immune system.

The problem with 'normal' cancers, is that the cells are from your own body and the immune response is not sufficient to control the tumours. But the antigens expressed by a different animal's tumour would be different, and highly immunogenic, I would think.

that is completely true, that is why DFTD is so interesting. because the gene pool is so small for the tasmanian devil population, the immune systems of these animals are having difficulty identifying self from foreign, which is why this disease is so devastating for their population. this really shows the importance of genetic diversity[/quote]

It is definitely quite possible that due to inbreeding, and general decrease in variation of genes, both the limited variation in immune-related genes (MHC mostly, for the recognition of foreign antigens) and limited variation in potential antigens (as the infectious cancer cells are seen by the newly infected Taz Devil) could lead to those cancer cells slipping past the immune system. Combine that with a possibility that the cancer cells could be producing their own immunosuppressive agents (as some cancers are known to do eg IL-10) and you have a very dangerous disease for the poor Devils :'(

As to the infectiosness of the cells, it's pretty amazing that simple contact can transfer them. Personally I would've thought that the uppermost layers of the skin that are capable of sloughing off (and hence transferring to another individual) would've generally been dead skin cells. But I guess since it's cancer it may be more resilient??

Also: http://www.medicalnewstoday.com/articles/174970.php
Just found this article today, most interesting. Haven't read the paper yet though.

Kinda interesting- there are human cells which could conceivably act in a similar manner. For example, most women who have given birth carry a very small population of cells from the child which do not illicit an immune response. They seem to be related to a kind of cell called mesenchymal stem cells which are being researched for their therapeutic potential (I've actually done some limited immunological studies with them myself). They have extremely versatile immunomodulatory properties which allow them to be transplanted between unrelated people without rejection- and humans are far more genetically diverse than the Tasmanian devil. A downside of this immune evasion is a risk of tumour formation.

Originally Posted by TheBiologista

Kinda interesting- there are human cells which could conceivably act in a similar manner. For example, most women who have given birth carry a very small population of cells from the child which do not illicit an immune response. They seem to be related to a kind of cell called mesenchymal stem cells which are being researched for their therapeutic potential (I've actually done some limited immunological studies with them myself). They have extremely versatile immunomodulatory properties which allow them to be transplanted between unrelated people without rejection- and humans are far more genetically diverse than the Tasmanian devil. A downside of this immune evasion is a risk of tumour formation.

Yes actually I had heard that about foetal tolerance (or whatever the correct terminology is). It kind of makes sense, considering the parts of the immune system that protect mucosal sites, eg the gastrointestinal tract, as well as the reproductive tract, have their own funny tweaks to the immune system, and given that the intestine actually dampens immune responses due to the presence of commensal bacteria! Also there may have been a pressure evolutionarily to lessen the immune responses in these areas to make them immunologically tolerant.

All that said, since Natural Killer cells are supposed to take care of any cancer cells forming, a study into NK cells in Taz Devils could be revealing....

The facial tumors may be introduced to the face through open wounds when fighting over food or by playful biting, during mating. Here's an article on the subject by David Quammen, one of my favorite naturalist authors:
http://www.harpers.org/archive/2008/04/0081988

earlier we mentioned two diseases. Devil Facial Tumor Disease and Canine Transmissible Venereal Tumour. Why aren't either of these called cancers? they seem to walk and talk like a cancer would?