Cancer: An Article and Question

So before I go to bed (it is 22:56 here in the UK) I thought I’d post this interesting BBC news article about a landmark cancer study (studies?) that folk may find interesting:

And also a question. Are cancers examples of one thing evolving into another thing? One of the common objections to evolution I rasied in my YEC days is that one species does not become another. Dogs produce dogs; cats cats; rats rats, repeat as desired.

However, it struck me that the change that takes place when, say, a skin cell turns into a skin cancer cell seems so dramatic a mutation that is it fair to say that it is still a skin cell? Doesn’t the mutation that takes place within the skin cell change it into something comparable to a new species when it becomes a skin cancer cell? In that sense is the change of a cell into a cancer cell a good example of evolutionary mechanisms in action? Why/why not?

As you all know, I’m not a biologist so please forgive my faltering use of language in attempting to explain what I meant. Hopefully, it makes sense. Particularly, welcome @sfmatheson thoughts and expertise on this one.

[Gracious] thoughts and/or course corrections welcomed. :slight_smile:

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We have discussed that a lot here. Just start reading the threads

https://discourse.peacefulscience.org/search?q=Cancer

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You beat me to it. :slight_smile:

It’s an interesting question, perhaps better seen as a metaphor or as a topic that provides opportunities to explore what it means to talk about a cell type or a species.

It is true that many (most?) cancers are characterized by spectacular collections of mutations–specifically, aneuploidy, which is a fancy word for the situation in which a cell has an abnormal number of chromosomes. In many cancers, the aneuploidy is extreme (the famous HeLa cell line, from a cervical cancer, has almost twice as many chromosomes as a normal human cell) and is accompanied by a benign-sounding thing called chromothripsis, which is a fancy word for “chromosomes blown apart then randomly stitched back together.” I think that it was HeLa cell genomic destruction that led scientists to first claim that a cancer cell could be a different “species” compared to the cells from which it came. “Mutation” seems too tame a word for it.

I would say yes and no. To me, it’s not the change from one cell “species” to another that is an evolutionary mechanism in action. For me, the clear evolutionary insight is the completely darwinian process that led to the “successful” tumor. This is an area of intense current research and analysis: the evolution of a cancer within an individual. It has every hallmark of classic evolution: populations and subpopulations, mutations and mutability, competition between subpopulations and between the cancer and the immune system, selection and even selective sweeps, genetic drift, the whole shebang. I pasted a couple of articles below, and I hope you notice the strong focus on evolutionary principles in these papers about cancer.

https://www.cell.com/cancer-cell/fulltext/S1535-6108(18)30469-0

https://www.cell.com/cell-reports/fulltext/S2211-1247(19)31359-2

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@Trunyon90 thanks for the link - will check it out.

Thanks @sfmatheson for this informative and helpful response. I knew you were the right person to ask.

I was particularly interested by aneuploidy and chromothripsis - these were completely new concepts for me. Also your description about the “completely darwinian process that [leads] to the “successful” tumor” was not something I had seen before. Definitely more thinking to do on that.

The links to the journals were a lovely icing on the cake. I’m looking forward to digging into them over the weekend.

May have some follow up questions i that’s ok… thanks again.

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Cancer cells can morphologically be typed as to their origin if not too dysplastic. In other words, you can look at a cancer under the microscope and make a good guess as to what sort of tissue it came from in many cases, so maybe still a skin cell in your example, but perhaps with what could be considered nested hierarchy if you look at it that way. Special stains can also help identify the tumor without looking at the genes, though genetic studies are becoming amazingly useful in identification and especially in treatment. Cancer is such a broad disease that it can better be considered as many different diseases.

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Thank you @LM77, @sfmatheson, @jpm and everyone else who has contributed to this thread. Such interesting ideas to think of cancer as a kind of parasitic organism looking to make its way in the world like the rest of us … and by way of the rest of us.

I’ve always heard it said cancer is (largely) reserved for the elderly. As such it has always seemed to me that cancer breaks down the body’s ability to self regulate as multi-cellular creatures. Personally I am in awe of the complexity of multicellular creatures in which initially independent cells learn to co-exist and cooperate, to the point where as self aware organisms we have no awareness of our individual cells or their origins. But our level of being is entirely dependent on that coordination and in some sense cancer seems to be the anarchy that ensues when it breaks down.

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I think there is something to be said for the immune system breaking down as we age. Your immune system can catch many cancers at very early stages, but we can lose that ability as we lose things like T cells.

The generalization I prefer to use for cancer is a group of cells that have lost their safety controls. Normal cells have several processes that prevent them from dividing uncontrollably, kind of like a deadman switch on a train. Mutations in these deadman switches is what causes cancer.

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What you say about the immune system seems very true. It has been suggested that we have cancer cells arise frequently in our bodies, but it is usually dealt with by our immune system or other regulatory mechanisms. On a practical basis, it really can complicate cancer screening. If you have a very sensitive test, you will find abnormal cells that the body will have gotten rid of on its own, without outside treatment. This is a problem with some DNA based screening blood tests. Once you find it, you are then left with the problem of what to do with that information. It can cause a lot of anxiety, expense, and even morbidity as further testing sometimes leads to complications.

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Going full circle, those are fundamental ethical questions relating to the cancer study in the opening post. If they find a weak association between a mutation and cancer, then what are the ethical questions we should have with genetic testing. What type of emotional burden does it place on the patient, and does it do more harm than good?

Speaking of complications, I was speaking to a colleague who is an infectious disease doc and he was treating someone who had a nasty infection from a prostate biopsy. A standard of care should absolutely consider risk and reward as we contemplate how genetics will influence medicine.

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