"Spontaneous" cancer development

[mark!]

I have a question regarding the development of cancer.

Cancer can be a genetical mutation inside a cell that can have an external/environmental cause, such as UV light, oncogenes in food sources, or with the help of oncoviruses and carcinogenic bacteria. Other than that, cancer is also said to be able to develop “spontaneously”. But this process doesn’t seem spontaneous to me.

The way in which a cancer cell cuts itself loose from the group after a cancer cell has grown (metastasis), and goes into the bloodstream to eat his way through the blood vessel (with the enzyme 'protease' and so-called MMPs to break the tissue), start increasing growth hormones, and prevents programmed cell death (apoptosis) but instead signals the body for blood vessels to grow towards the cancer cell (angiogenesis) and telomerase becomes active to make sure this process can’t be stopped.

This doesn't seem solely and purely mechanical and spontaneous, rather it behaves like a pathogen. Cancer cells suppress the immune system (or evade immune responses by disrupting those cells, signals an receptors) the same way pathogens do. Viruses for instance can neutralise the major histocompatibility complex (MHC) which cells use to present antigens to the immune system. Tumors do this as well, so there are similar mechanisms to avoid detection and destruction, and they resemble pathogens in manipulative ability.

What I don’t understand is how this step-by-step process can be initiated by a cancer cell if it's considered a lifeless “spontaneous” consequence of “random” mutations. Lots of pathogenic parasites also show a step-by-step process, and need several hosts to end up in the host they finally need to reproduce in. Tapeworms and other parasitic flatworms for instance have complex lifecycles in which specific developmental stages are completed in a sequence of several different hosts.

Is this really a spontaneous event? Or are viruses and cancer cells perhaps not 100% lifeless? Where is this desire in cancer, viruses and other pathogens to reproduce coming from?

 

[Ygggdrasil]

When people talk about cancer arising spontaneously, they just mean that the mutations likely arose from normal errors made during DNA replication (as opposed to being induced by some external agent). For a discussion about the origins of the mutations that cause cancer, see: https://www.physicsforums.com/insights/causes-cancer-bad-luck-bad-lifestyles/

Cancer can arise from a bunch of spontaneous, random mutations because carcinogenesis is an evolutionary process. Cells that gain mutations that help promote the "hallmarks of cancer" (uncontrolled growth, immune system evasion, resistance to apoptosis, etc.) are able to replicate and pass on their mutations to a new generation of cells; cells lacking these mutations do not grow and are outcompeted by the other cells in the tumor.

Essentially, the "desire" that causes reproduction of cancer, viruses, and pathogens is the process of evolution and the concept of survival of the fittest. The individual viruses, cancer cells, and pathogens that can reproduce the fastest and most efficiently will survive to make new progeny, while those that reproduce at a slower rate will be outcompeted.

 

[mark!]

Thanks for the insights-article!

By using terms like “evolutionary process” and “survival of the fittest”, words that are intimately connected to life, are you thereby supporting the notion that this “desire” of cancer to reproduce itself, can and may not be viewed as a mechanical lifeless event?

 

[Ygggdrasil]

Cancer cells are living, so they are subjected to evolutionary forces.

There are even examples of infectious cancers that can spread beyond their individual host and propagate across a population as a viral or bacterial infection would. See for example canine transmissible veneral tumor disease or devil facial tumor disease. Here's a nice popular press article about DFTD: https://www.theatlantic.com/science...n-tasmanian-devils-baffles-scientists/423012/

 

[pinball1970]

Where is this desire in cancer, viruses and other pathogens to reproduce coming from?

Desire suggests purpose and this is not the case with viruses or cancer cells.Some genes make proteins in the cell and if the regulatory measures in the rest of the genome/cell are not in place the system can go haywire.Too much of a protein can be manufactured not enough or the wrong amino sequence.This can affect cell function lead to disease cell death or cancer.

 

[Laroxe]

I think you might be thinking of desire as something requiring awareness, I think in this case its being used to reflect one of the basic things that can be used to define life itself and that is the drive to reproduce. Cancer is really a collection of diseases which can make some generalizations difficult but its clear random mutations in cells do take place most often during cell reproduction, mistakes can occur during the copying of the DNA, most will be detected at the time and the cell destroyed. However some minor mistakes may not trigger this process and the cell is allowed to survive and is capable of passing on the defect and such defects can accumulate. If these defects initially interfere with the cells responses to specific signaling molecules, particularly those that govern reproduction this can cause problems. However cells are constantly monitored and defects lead to the immune system triggering apoptosis, instructing the cell to die.
There are some particular issues that cause problems, its not that cancer cells reproduce in an uncontrolled manner, many in fact don't, its the fact that cells with particular defects become much more likely to develop more and that these cells increasingly start to behave as an individual organism rather than part of the human body. So as cancers develop the cells often become increasingly different to the parent cell and in promoting its own reproduction, evolutionary processes promote the fitness of cells with defects that favor its reproduction. Some of these are well known features of cancer, they can ignore signals controlling reproduction, specific function, location, signals to suicide and they may develop ways to avoid immune surveillance, migrate and spread, disrupt and invade other tissues. Features that enable them to signal for extra nutrients are preserved.
I read a recent article that suggested that cancer may reflect an unraveling of the evolutionary changes that have created complex organisms with cell specialization and organization at the level of the organism. Some of the cells identified in tumors become so different they can be difficult to identify microscopically, even as human. The explicit involvement of evolutionary processes is currently a topic of considerable research interest at the moment and the increasing understanding of the genetic control of cell signalling molecules has lead to an explosion of new drugs for cancer treatment.

 

[rootone]

Where is this desire in cancer, viruses and other pathogens to reproduce coming from?

Is the same 'desire' that any DNA has, but it turns out to be destructive for the higher organism which is infected,
There is a whole class of life, fungi. which operate on breaking down of proteins and recycling the debris.

 

[mark!]

I think you might be thinking of desire as something requiring awareness, I think in this case its being used to reflect one of the basic things that can be used to define life itself and that is the drive to reproduce. Cancer is really a collection of diseases which can make some generalizations difficult but its clear random mutations in cells do take place most often during cell reproduction, mistakes can occur during the copying of the DNA, most will be detected at the time and the cell destroyed. However some minor mistakes may not trigger this process and the cell is allowed to survive and is capable of passing on the defect and such defects can accumulate. If these defects initially interfere with the cells responses to specific signaling molecules, particularly those that govern reproduction this can cause problems. However cells are constantly monitored and defects lead to the immune system triggering apoptosis, instructing the cell to die.
There are some particular issues that cause problems, its not that cancer cells reproduce in an uncontrolled manner, many in fact don't, its the fact that cells with particular defects become much more likely to develop more and that these cells increasingly start to behave as an individual organism rather than part of the human body. So as cancers develop the cells often become increasingly different to the parent cell and in promoting its own reproduction, evolutionary processes promote the fitness of cells with defects that favor its reproduction. Some of these are well known features of cancer, they can ignore signals controlling reproduction, specific function, location, signals to suicide and they may develop ways to avoid immune surveillance, migrate and spread, disrupt and invade other tissues. Features that enable them to signal for extra nutrients are preserved.
I read a recent article that suggested that cancer may reflect an unraveling of the evolutionary changes that have created complex organisms with cell specialization and organization at the level of the organism. Some of the cells identified in tumors become so different they can be difficult to identify microscopically, even as human. The explicit involvement of evolutionary processes is currently a topic of considerable research interest at the moment and the increasing understanding of the genetic control of cell signalling molecules has lead to an explosion of new drugs for cancer treatment.

That's very interesting! This is the kind of information I was looking for.

The most interesting part of what you’re describing is that cancer actually starts to behave as an individual organism. The way cancer is currently being explained seems too mechanical, as if it’s some kind of biological glitch, but in reality it’s a cell that becomes a pathogenic individual in some way, that isn't part of the body's identity anymore.

The examples you’re describing show this characteristic perfectly: cancer cells ignore signals that want to control reproduction, they develop ways to avoid immune surveillance, they migrate and spread throughout the body, and they disrupt/invade other tissues. Exactly as an animal-like pathogen would do, in its own advantage to survive, because it needs food, and because it needs to reproduce. Of course the cancer cell doesn't "know" it's actually on a suicide mission, instead of winning from the rest.

You were saying that many cancer cells don’t reproduce in an uncontrolled manner. What are they doing instead?

You were referring to an article you’ve read, about cancer and complex organisms with cell specialisation. What article were you referring to? I think I want to read this article as well.

 

[mark!]

Desire suggests purpose and this is not the case with viruses or cancer cells.

Some genes make proteins in the cell and if the regulatory measures in the rest of the genome/cell are not in place the system can go haywire.

Too much of a protein can be manufactured not enough or the wrong amino sequence.

This can affect cell function lead to disease cell death or cancer.

It's complicated, because this so-called "desire" is also influencing micro organisms in the vicinity that also have the same "desire" to reproduce. For example, a tumour is often accompanied by the same of infamous oncoviruses or carcinogenic bacteria (who insert their genome into cancer cells). Species of bacteria that are known to be harmful, like Fusobacterium Nucleatum (who normally habitates the mouth), or Streptococcus Bovis (often present near intestinal tumors) are often present when cancer cells develop. Species of bacteria that are harmless, and behave moderate and quiet in normal circumstances, all of a sudden start to behave aggressive, but only if they’re being encouraged to do so by these harmful bacteria. They start to help overthrowing the immune system, which is in the advantage of the cancer cell (that shows similar mechanisms to avoid detection and destruction by the immune system).

How these opportunistic microbes are influenced by the change of the environment, isn't quite clear to me, but this shows that the ambiance/ethos must somehow influence the development of cancer as well.

 

[pinball1970]

How these opportunistic microbes are influenced by the change of the environment, isn't quite clear to me, but this shows that the ambiance/ethos must somehow influence the development of cancer as well.

Microbes do take advantage of weakened immune systems KS (Kaposi' sarcoma) being an example in AIDs patients and there plenty of the others. The environment in this case is the immunosuppressed individual

https://en.wikipedia.org/wiki/Kaposi's_sarcoma

Have you read much on telomerase activity and cancer? Its interesting and Nessa Carey wrote a great book on this and many other aspects of the genome that do not code for proteins "Junk DNA"

Matt Ridley mentions telomere activity and cancer in his book "Genome" - Good read around for your studies/research

 

[pinball1970]

For example, a tumour is often accompanied by the same of infamous oncoviruses or carcinogenic bacteria (who insert their genome into cancer cells).

Plenty on that too and also ERVs

 

[Ygggdrasil]

It's complicated, because this so-called "desire" is also influencing micro organisms in the vicinity that also have the same "desire" to reproduce. For example, a tumour is often accompanied by the same of infamous oncoviruses or carcinogenic bacteria (who insert their genome into cancer cells). Species of bacteria that are known to be harmful, like Fusobacterium Nucleatum (who normally habitates the mouth), or Streptococcus Bovis (often present near intestinal tumors) are often present when cancer cells develop. Species of bacteria that are harmless, and behave moderate and quiet in normal circumstances, all of a sudden start to behave aggressive, but only if they’re being encouraged to do so by these harmful bacteria. They start to help overthrowing the immune system, which is in the advantage of the cancer cell (that shows similar mechanisms to avoid detection and destruction by the immune system).

How these opportunistic microbes are influenced by the change of the environment, isn't quite clear to me, but this shows that the ambiance/ethos must somehow influence the development of cancer as well.

The connections between bacteria and cancer is still very unclear and researchers are still working out whether connections that have been seen by some groups are real and relevant to the disease. The paper you cite that claims bacteria insert their genome into cancer cells is based on a technique known to have issues with contamination (see discussion in this previous thread: https://www.physicsforums.com/threads/the-role-of-bacteria-in-cancer-development.937971/). Before I would believe the study, I would like to see confirmation of their findings using an independent method that is not so prone to contamination artifacts. Furthermore, even if their results are true, they don't show evidence that the bacteria are acting in any carcinogenic way.

While there is evidence for bacteria like Fusobacterium nucelatum co-occuring with certain cancers (https://www.ncbi.nlm.nih.gov/pubmed/22009989) and preliminary evidence that the bacteria could enhance cancer cell proliferation (http://science.sciencemag.org/content/early/2017/11/20/science.aal5240), other studies have failed to replicate some of these results (https://elifesciences.org/articles/25801). More research is needed before we begin drawing too many conclusions from these studies, so it's much too early to begin speculating that the "desire" of the cancer cells to reproduce is directly influencing the micro-organisms in their vicinity.

Most biologists would also have issues with characterizing these cells as having a "desire" to reproduce. Use of that term unnecessarily anthropomorphizes the behavior of these cells. Bacteria and other pathogens are programmed by their DNA to reproduce whenever they are in a suitable environment with plenty of resources. Human cells early in development also have this programming, but in the adult organism, this programming gets shut off in favor of programming that relies on intercellular signaling so that cells in the body can coordinate and work together. In cancer, mutations chip away at this programming such that these cells begin to act more as individuals and ignore signals from its surrounding cells and the rest of the body. During carcinogenesis, cells that acquire mutations enabling faster replication and better avoidance of signals from the body to stop replicating will reproduce more quickly than other cells, enabling these cells to evolve into cancer cells. These cells act very much like other pathogens in the body and could even be considered a separate pathogenic organism living in the body (for example, the immune system often recognizes cancer cells as foreign).

There are definitely bacteria in the vicinity of many cancers, but the role they play is still unclear. Tumors will often contain many dead and dying cells, which could provide a good environment for fostering bacterial growth. In this case, cancer would be causing the bacteria to co-occur with the tumor. Alternatively, as you are suggesting, bacteria could co-occur with tumors because the bacteria may aid in the transformation of normal cells to cancer cells. The direction of this causation is still unclear.

 

[Laroxe]

That's very interesting! This is the kind of information I was looking for.

The most interesting part of what you’re describing is that cancer actually starts to behave as an individual organism. The way cancer is currently being explained seems too mechanical, as if it’s some kind of biological glitch, but in reality it’s a cell that becomes a pathogenic individual in some way, that isn't part of the body's identity anymore.

The examples you’re describing show this characteristic perfectly: cancer cells ignore signals that want to control reproduction, they develop ways to avoid immune surveillance, they migrate and spread throughout the body, and they disrupt/invade other tissues. Exactly as an animal-like pathogen would do, in its own advantage to survive, because it needs food, and because it needs to reproduce. Of course the cancer cell doesn't "know" it's actually on a suicide mission, instead of winning from the rest.

You were saying that many cancer cells don’t reproduce in an uncontrolled manner. What are they doing instead?

You were referring to an article you’ve read, about cancer and complex organisms with cell specialisation. What article were you referring to? I think I want to read this article as well.

Its always a problem working from memory, particularly at my age but I did eventually findsome references to it. The articles I had read were in relation to Paul Davis becoming involved in cancer research and his ideas around evolution. However as I was looking I did come across a wider discussion that suggests that all is not well with the basic ideas. The links do provide an overview of his ideas along with some criticism. The first being by David Gorski a not insignificant figure in surgical oncology. The others all have information you might find useful and the ncbi links have further links to other resources.

https://respectfulinsolence.com/201...-cancer-lectures-cancer-biologists-on-cancer/

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3711102/

https://www.ncbi.nlm.nih.gov/pubmed/17109012/

https://medicalxpress.com/news/2018...&utm_medium=email&utm_campaign=daily-nwletter

 

[mark!]

It took me some time to read all the articles everybody has provided me, but I’ve finally finished them all, so let me now give a proper reaction to your comments.

I’ve just started reading the book you’ve recommended, @pinball1970. In Matt Ridley’s book ‘Genome’ he argues that the first organisms were not like bacteria but more like protozoa, with genes fragmented into several linear chromosomes, rather than one circular chromosome, and also polyploid as a back up in case of genetic mistakes (page 20). He continues by stating that the idea that life started with bacteria, and all other life forms came later, isn’t right. It’s more probable that bacteria have dropped the machinery (which they've inherited from the RNA world hypothesis) to be able to live in hot places, rather than later life forms developing them in a later stage of evolution (which is also supported by the degeneracy hypothesis of viruses, which states that viruses come from small primordial cells which lost their cellular elements in the course of evolution). Our cells contain unnecessary rudimentary RNAs. Bacteria have none of these. Why for instance does our sperm have so much RNA? According to Matt Ridley, this is a rudimentary trait, because bacteria presumably dropped their RNA world machinery to be able to live in the heat.

If life started as single celled protozoa-like single celled organisms, this made me think of the article that @Laroxe provided. This article is a critical and cynical reaction to this original article by Davis. In the original article it's being argued that way in which cancer is behaving, it is in fact going back into ancient times. A controversial idea, but the explanation is not as far-fetched as Gorski wants us to interpret it. Cancer creates its own acid environment (an environment reminiscent of the atmosphere with much higher amounts of CO2, called the Proterozoic Eon, 1.5 billion years ago), and furthermore, cancer metabolism isn’t using oxygen the way our cells do (which must have been also the way metabolism took place 1.5 billion years ago). Most cancer cells predominantly produce energy by a high rate of glycolysis followed by lactic acid fermentation in the cytosol. In comparison, the majority of parasites, such as tapeworms, do not use the oxygen available within the host, but use anaerobic respiration, or adapt to low oxygen tension using metabolic systems that are very different from that of the host. All these things considered, I don't yet share Gorski's cynicism on Davis' remarks.

I’ve read (and finished) the other book you've mentioned, written by Nessa Carey, called ‘Junk DNA’. I also recommend this to everybody. She writes for instance that Junk DNA, better known as 'noncoding DNA', also consists of noncoding RNA. ncRNA causes alterations in the behaviour of cancer cells (see page 108). Moreover, overexpression of ncRNA makes cancer cells more likely to metastasis. The most primitive/basic functions in the human cell require presence of RNA. Ribosomes themselves are partly made up of ncRNAs (3 ncRNAs in prokaryotes and 4 ncRNAs in eukaryotes), which again reminds me of the basic/ancient nature and behaviour of cancer, described by Davis. Ancient long ncRNAs are actively regulated in organisms, and mostly involved in early development (and present in our sperm), which makes perfect sense because all vertebrates look alike in the fetal stage (see page 99).

@Ygggdrasil, on the notion that there are bacteria in the vicinity of many cancers, you've said that the “role they play is still unclear” and “the direction of this causation is still unclear”. Is this really unanimously the case within the entire scientific community? Because I was referring to a statement of a biomedical scientist who did research on this behaviour of bacteria near cancer, and wrote in his book that when some species of bacteria that are usually harmless wind up in the vicinity of a developing tumour, they can act as a precursor of cancer. They can derail completely, and change their behaviour by turning from moderate and harmless to being rogue and harmful, and all of a sudden start to attack the immune system and also insert their genome into these tumours. This was not explained as a ‘maybe’ and ‘we’re still working on it’, rather it was stated a biological fact about these bacteria. Unfortunately, I’ve never found any paper about this interesting idea. Maybe I should send him an e-mail, because I really would like to know more about this behaviour of bacteria, who apparently are morally influenced by the ambiance of the environment.

 

[BillTre]

In Matt Ridley’s book ‘Genome’ he argues that the first organisms were not like bacteria but more like protozoa, with genes fragmented into several linear chromosomes, rather than one circular chromosome, and also polyploid as a back up in case of genetic mistakes (page 20). He continues by stating that the idea that life started with bacteria, and all other life forms came later, isn’t right. It’s more probable that bacteria have dropped the machinery (which they've inherited from the RNA world hypothesis) to be able to live in hot places, rather than later life forms developing them in a later stage of evolution (which is also supported by the degeneracy hypothesis of viruses, which states that viruses come from small primordial cells which lost their cellular elements in the course of evolution).

This is wrong.
There is no way eukaryotic cells evolved before bacteria!
There are older fossils of bacteria-like cells than any of eukaryots.
Gene sequence comparisons do not support this idea.
From a cell structure point of view, it is non-parsimonious. Eukaryotic cells are way more complex and contain bacterial remnants within them (mitochondria). It is more parsimonious to assume something simpler (bacteria) evolved before the more complex eukaryotic cell.

I looked up his book on wikipedia and it reception is "mixed", including parts where: "Ridley speculates, "sometimes wildly"".

 

[pinball1970]

I looked up his book on wikipedia and it reception is "mixed", including parts where: "Ridley speculates, "sometimes wildly"".

Chapter 6 aside I thought the book was good.

 

[pinball1970]

This is wrong.
There is no way eukaryotic cells evolved before bacteria!

I don't remember him saying this. Ill check

 

[mark!]

This is wrong.
There is no way eukaryotic cells evolved before bacteria!
There are older fossils of bacteria-like cells than any of eukaryots.
Gene sequence comparisons do not support this idea.
From a cell structure point of view, it is non-parsimonious. Eukaryotic cells are way more complex and contain bacterial remnants within them (mitochondria). It is more parsimonious to assume something simpler (bacteria) evolved before the more complex eukaryotic cell.

I looked up his book on wikipedia and it reception is "mixed", including parts where: "Ridley speculates, "sometimes wildly"".

I said protozoa-like. Of course eukaryotes came after prokaryotes. I support the endosymbiosis hypothesis between an archaeon and a bacterion. 'Protozoa-like' is a reference to a way of living, a way of behaving.

Viruses, in some way, are also protozoa-like in their behaviour. Compare the way viruses can be dependant on their hosts just like some protozoa are. Compare how protozoa (such as Dicrocoelium Dendriticum) as well as viruses (such as Baculoviridae) are able to manipulate their host. Compare how one virus invades a cell, and millions of viruses come out (while the cell bursts open and dies) with the way that the Plasmodium parasite (malaria) invades a red blood cells (while the cell bursts open and dies). Furthermore, the malaria parasite has survived for more than 50,000 years, and natural selection favours strains of the organism with mutations that help them evade threats. This means that protozoa are able to mutate, just like viruses, such as influenza, are able to.

Thus, only viruses existed alongside bacteria during the Proterozoic Era (such as bacteriophages). I did not say that protozoa (single celled eukaryotes) came before prokaryotes. That would be terribly wrong, as you’ve correctly remarked .

 

[pinball1970]

I looked up his book on wikipedia and it reception is "mixed",

I am little shocked that one of those mixed reviews is from Jerry Coyne ("Why Evolution is true")

Genome features in Dawkins book "Oxford book of modern science writing" He gave it a great review and said he used the same approach for the "Ancestors tale." Genome may be a little out of date but I rated it.

 

[Ygggdrasil]

@Ygggdrasil, on the notion that there are bacteria in the vicinity of many cancers, you've said that the “role they play is still unclear” and “the direction of this causation is still unclear”. Is this really unanimously the case within the entire scientific community? Because I was referring to a statement of a biomedical scientist who did research on this behaviour of bacteria near cancer, and wrote in his book that when some species of bacteria that are usually harmless wind up in the vicinity of a developing tumour, they can act as a precursor of cancer. They can derail completely, and change their behaviour by turning from moderate and harmless to being rogue and harmful, and all of a sudden start to attack the immune system and also insert their genome into these tumours. This was not explained as a ‘maybe’ and ‘we’re still working on it’, rather it was stated a biological fact about these bacteria. Unfortunately, I’ve never found any paper about this interesting idea. Maybe I should send him an e-mail, because I really would like to know more about this behaviour of bacteria, who apparently are morally influenced by the ambiance of the environment.

I can't speak for the entire scientific community, but I am still skeptical of some of these links. There is some evidence for the hypothesis and many researchers are following up on these leads, but I don't think these connections have been conclusively shown yet. Whenever you mention bacteria inserting their genomes into cancer cells you cite a single paper based on a single technique known to have problems with contamination. Before you accept that assertion as fact, I would like to see confirmation of their findings by independent techniques.

 

[BillTre]

I said protozoa-like. Of course eukaryotes came after prokaryotes. I support the endosymbiosis hypothesis between an archaeon and a bacterion. 'Protozoa-like' is a reference to a way of living, a way of behaving.

Well that's good to know since protozoa are eukaryotes. They are way bigger and way more complex than bacteria.

Protozoa-like' is a reference to a way of living, a way of behaving.

Viruses, in some way, are also protozoa-like in their behaviour. Compare the way viruses can be dependant on their hosts just like some protozoa are. Compare how protozoa (such as Dicrocoelium Dendriticum) as well as viruses (such as Baculoviridae) are able to manipulate their host. Compare how one virus invades a cell, and millions of viruses come out (while the cell bursts open and dies) with the way that the Plasmodium parasite (malaria) invades a red blood cells (while the cell bursts open and dies). Furthermore, the malaria parasite has survived for more than 50,000 years, and natural selection favours strains of the organism with mutations that help them evade threats.

This is describing a parasitic lifestyle not a protozoan lifestyle. Protozoan lifestyles are very diverse.
The wikipedia entry above says this about protozoan behavior:

free-living or parasitic, which feed on organic matter such as other microorganisms or organic tissues and debris.

There are also bacterial parasites and could well be archean parasites (I don't know). In addition, there are fungal parasites, metazoan (multicellular animals) parasites (here are some that affect zebrafish), and even parasitic plants that are dependent upon their hosts.
Any organism with a parasitic lifestyle could well acquire, through natural selection, mutations that will enhance its lifestyle.
You should be more selective in your use of words if you want to clearly convey your intended meaning.

I don't understand the point of these quoted sentences:

Furthermore, the malaria parasite has survived for more than 50,000 years, and natural selection favours strains of the organism with mutations that help them evade threats. This means that protozoa are able to mutate, just like viruses, such as influenza, are able to.

Everything biological acquires mutations and is subject to the actions of selection.
Neither of those traits distinguishes any biological entity from any other biological entity.
Mutation and the spread of new mutations through a population is not something only nasty parasitic organisms do. This is the basis of evolution which affects all organisms.
They are universal traits. People, plants, animals, fungi, protozoans, bacteria and archea all do these things.
Having their mutations selected for if they favor a parasitic lifestyle could happen in any of these cases.

 

[Laroxe]

I think most of the posts are urging caution with these ideas Mark, while cancers are subject to the principles of selection, you seem to want to believe that this is in some way directed or directional and this falls outside of or counter to our current understanding. As cancers progress genetic mutations accelerate but there is no general direction with individual cells going in all sorts of directions and as is usually the case with mutations a great many are incompatible with life. In any tumor mass only a minority of the cells are alive and active.
I don't think Davis's ideas generated a dismissive emotional reaction, there are very good theoretical and evidenced based reasons to doubt them, in the same way some of Ridleys ideas are based on some rather fast and loose reasoning, and generally I enjoy his books. Remember that most of the cells in a tumor will be in a hypoxic environment, so the survivors will have adapted to this, hypoxic environments are more acidic and must be able to generate energy in a low resource environment. This is selection based on the current environmental conditions as it should be, not on any evolutionary direction. I've never understood why some vague similarities in developing embryo's are suggested as something meaningful while the more obvious huge differences are ignored. The way in which collections of cells develop into a complex organism follows very similar developmental stages and so some similarities are inevitable but you only really have to add variables like the time following conception and the whole idea falls apart. At the point human organs have formed a great many animals have already been born.
Anyway this is a discussion on the effects of random mutations
http://blogs.discovermagazine.com/d-brief/2017/03/23/cancer-random-chance-mutations/#.WsaCsbj1S6k
I thought you might be interested in this review of the evidence for infections which was published in the Lancet in 2008, it attributes 16% of cancers worldwide to infections
http://www.thelancet.com/journals/lanonc/article/PIIS1470-2045(12)70137-7/fulltext#article_upsell
A critique of this paper in 2012 saw no reason to challenge this estimate.
http://www.thelancet.com/journals/lanonc/article/PIIS1470-2045(12)70176-6/fulltext