Cancers Are Newly Evolved Parasitic Species

[Pappa]

Cancers Are Newly Evolved Parasitic Species, Biologist Argues
http://www.popsci.com/science/article/2 ... ist-argues

Cancer patients may feel like they have alien creatures or parasites growing inside their bodies, robbing them of health and vigor. According to one cell biologist, that’s exactly right. The formation of cancers is really the evolution of a new parasitic species.

Just as parasites do, cancer depends on its host for sustenance, which is why treatments that choke off tumors can be so effective. Thanks to this parasite-host relationship, cancer can grow however it wants, wherever it wants. Cancerous cells do not depend on other cells for survival, and they develop chromosome patterns that are distinct from their human hosts, according to Peter Duesberg, a molecular and cell biology professor at the University of California-Berkeley. As such, they’re novel species.

He argues that the prevailing theories of carcinogenesis, or cancer formation, are wrong. Rather than springing from a few genetic mutations that spur cells to grow at an uncontrolled pace, cancerous tumors grow from a disruption of entire chromosomes, he says. Chromosomes contain many genes, so mis-copies, breaks and omissions lead to tens of thousands of genetic changes. The result is a cell with completely new traits: A new phenotype.

Cancer as evolution in action, which represents a fundamental re-thinking of the disease, has been proposed before — evolutionary biologist Julian S. Huxley first described autonomously growing tumors as a new species back in 1956, according to a Cal news release. But the prevailing view has long been that cancer is the result of genetic mutations.

Oncologists and pharmaceutical researchers are studying ways to find and block those mutations, aiming to turn off the switch that sparks carcinogenesis. But gene therapy has largely failed to deliver many meaningful results.

Duesberg argues, controversially, that it's misguided. Chromosomal mutation, called aneuploidy, is the cause instead, and it destabilizes chromosomal patterns. Some of the disrupted chromosomes are able to divide, seeding cancer. The result is a new chromosomal pattern that is distinct from our own. The Cal news office explains this in much greater detail.

Duesberg said he hopes this theory will spark new types of cancer diagnosis and treatment. Chromosomal tests could potentially pick out aneuploidy very early, before the damaged chromosomes have had a chance to divide, for instance. And new treatments could target the chromosomal disruptions, rather than knocking out or switching off genes.

[Gallstones]

Interesting hypothesis.
I don't think it is quite an accurate fit for the situation, but interesting idea.

[Berthold]

Well, until now I regarded Duesberg mainly as a dangerous crackpot, but it seems there's more to the guy.

[Pappa]

The concept doesn't actually add anything new or change anything. Regardless of whether the idea has any validity, it's simply a semantic issue really.

[GenesForLife]

Old news.

[mistermack]

One thing about a species is that it has the ability to reproduce itself.
A cancer can do that, until the host dies, then it's fucked, totally extinct.
Maybe a similar one will occur in another animal, but it's not descended from any other cancer.
Until contagious cancer appears, you can hardly call cancer a species.

I suppose you could argue that it's contagious, if your children inherit the same possibility of cancer. But it's going against evolution for something that sickens and kills it's host to evolve in the first place, unless it can jump to another victim.

Evolution works on success, not failure. The genes that are involved in producing cancers can't spread in a population, unless they also bring a real benefit to the organism.
They are competing with similar genes that don't cause cancer, after all.

Maybe cancers are mechanisms that species have evolved to remove the older individuals from the scene, when they get past a healthy breeding age, so that they don't compete with the young.

[Robert_S]

Maybe cancers are mechanisms that species have evolved to remove the older individuals from the scene, when they get past a healthy breeding age, so that they don't compete with the young.

I kinda doubt it since not many of us ever got to cancer age for a lot of our history.

[Gawdzilla Sama]

I wonder if this news, "old" or not, is inspiring new methods of dealing with cancers? [/personal interest]

[mistermack]

Maybe cancers are mechanisms that species have evolved to remove the older individuals from the scene, when they get past a healthy breeding age, so that they don't compete with the young.

I kinda doubt it since not many of us ever got to cancer age for a lot of our history.

There you are! It works great!

[GenesForLife]

One thing about a species is that it has the ability to reproduce itself.
A cancer can do that, until the host dies, then it's fucked, totally extinct.
Maybe a similar one will occur in another animal, but it's not descended from any other cancer.
Until contagious cancer appears, you can hardly call cancer a species.

I suppose you could argue that it's contagious, if your children inherit the same possibility of cancer. But it's going against evolution for something that sickens and kills it's host to evolve in the first place, unless it can jump to another victim.

Evolution works on success, not failure. The genes that are involved in producing cancers can't spread in a population, unless they also bring a real benefit to the organism.
They are competing with similar genes that don't cause cancer, after all.

Maybe cancers are mechanisms that species have evolved to remove the older individuals from the scene, when they get past a healthy breeding age, so that they don't compete with the young.

The cancer cells are the organism. When tumours grow, the frequency of alleles specific to cancer cells increases within the population of tumour cells. As far as host-dependence is concerned, look up cancer cell lines such as HeLa, which establish themselves in culture media et cetera and if conditions permit, overpower resident cells and continue to grow indefinitely, demonstrating that existence and proliferation outside of the source of the tumour is possible.

Compared to normal cells, tumour cells have higher fitness because they produce more offspring than normal cells, that is where the selective advantage is. Whether cancers are contagious or not is irrelevant insofar the attribution of the term "species" is concerned; since for asexually reproducing organisms, species are made of single cells (and if clonally identical, daughter cells too) (the correct term would be Phylotype, IIRC)

A parasite that kills its host and cannot spread further is as much a species as is one that does not kill its host and spreads further, to assert otherwise is to be absurd.

[GenesForLife]

I wonder if this news, "old" or not, is inspiring new methods of dealing with cancers? [/personal interest]

Actually, it is.

The identification of the fact that heterogeneity is a major feature of cancer cells is already being pressed into service for things such as determining prognosis using microarrays et cetera, for starters. Finding drug targets is also another useful area of activity, for examples, recognizing that cancers are different and different cancers have different sets of genes driving their pathology can make it possible to either target cancers individually, or if groups with similar underlying elements can be found, develop drugs to target those elements, one such example is the blockbuster drug Gleevec, which is used to treat Chronic Myelogenous Leukaemia. Such an approach has also led to some degree of broadening in the degree of precision in the characterisation of tumours, which will, it is hoped, improve therapeutic management.

Treating cancer cells as evolving species also brings with it a distinct advantage; by looking at cancer cells versus normal cells through an evolutionary lens, you can seek to identify genes that are vital to cancer cells but not normal cells, which then automatically enables one to develop therapies that are particularly specific to cancer cells, one example would be telomerase, which cancer cells need and express but normal cells do not. Another would be the discovery and development of adenoviruses that can replicate only in cancer cells based on the exploitation of a vulnerability in cancer cells. This is particularly smart, normal adenoviruses that can grow in normal cells use a pair of genes called E1A and E1B to knock out two genes called pRb and p53, mutants that lack E1A and E1B cannot grow in normal cells, but because cancer cells usually have missing pRb and p53 (one or both) as a pre-requisite for turning malignant, such viruses can replicate in cancer cells, specifically.

I'll be back with more later.

[JimC]

One thing about a species is that it has the ability to reproduce itself.
A cancer can do that, until the host dies, then it's fucked, totally extinct.
Maybe a similar one will occur in another animal, but it's not descended from any other cancer.
Until contagious cancer appears, you can hardly call cancer a species.
I suppose you could argue that it's contagious, if your children inherit the same possibility of cancer. But it's going against evolution for something that sickens and kills it's host to evolve in the first place, unless it can jump to another victim.

Evolution works on success, not failure. The genes that are involved in producing cancers can't spread in a population, unless they also bring a real benefit to the organism.
They are competing with similar genes that don't cause cancer, after all.

Maybe cancers are mechanisms that species have evolved to remove the older individuals from the scene, when they get past a healthy breeding age, so that they don't compete with the young.

Facial tumours in the Tasmanian Devil are spread from individual to individual by biting. Apparently, this rather novel situation can occur because \of the low level of genetic variation in the Devil population.

[GenesForLife]

And oh, Mistermack, nobody has said that cancer is a species, they've said that every tumour is a new species, no requirement for being transmissible at all.

[Xamonas Chegwé]

Tumours can be transmitted via dodgy transplants or transfusions - I saw it on House!

[JimC]

Tumours can be transmitted via dodgy transplants or transfusions - I saw it on House!

One would think this would be a very rare occurence, unless the recipient was severely immuno-supressed. Successful cancer cells seem to be able to fool their own body's immune system, but it would be much harder to escape the attentions of a genetically different immune system. The reason why it works in the Tassie Devil poputation is because of their low genetic diversity; yet another example where the genetic diversity of a population is pivotal in its chances of going extinct...

Also, I remember reading a NewScientist article which suggested that everybody develops incipient cancer cells quite often, but almost all of the time, they are recognised and destroyed by the immune system. I gather that one line of cancer research is all about investigating the factors that give succesful cancer cells their ability to hide from the immune system...