Why does cancer spread?

The Human Body -- Cancer
The Human Body — Cancer (Photo credit: n0cturbulous)

Everyone, I’m sure, knows of someone who has died of cancer. It’s a disease that is wide-spread and seems to be more common now that other diseases are coming under control. It may be that cancer is certain to appear in the human body if it lives long enough. There’s a cheery thought.

Wikipedia describes cancer as follows: “known medically as a malignant neoplasm, (it) is a broad group of diseases involving unregulated cell growth. In cancer, cells divide and grow uncontrollably, forming malignant tumours, and invade nearby parts of the body”.

Cross section of a human liver, taken at autop...
Cross section of a human liver, taken at autopsy examination, showing multiple large pale tumor deposits. The tumor is an adenocarcinoma derived from a primary lesion in the body of the pancreas. (Photo credit: Wikipedia)

There’s two parts of this definition. Firstly there is the unregulated cell growth and secondly there is the spread of the growth to other parts of the body. The unregulated cell growth is usually attributed to a number of causes, but the mechanism is usually given as damage to the genetic material. The causative agent whatever it might be, damages the genetic material and this results in a huge proliferation of cells.

I write computer programs as tools for doing my job. Each program ends up as a string of data which a human has a hard time decoding, though of course the computer hardware has no problems. The effect of changing a single bit (actually, a byte) of a program would almost certainly cause it to crash. In so far as the analogy that the genetic code resembles a computer program holds, this indicates that a random change to the genetic code would most likely result in the death of the cell. It would require a specific hit, to say a piece of code that control the termination of a loop that would let the program “grow out of control”.

Out of memory ATM
Out of memory ATM (Photo credit: RuiPereira)

I’d guess, from a position of almost total ignorance, that changes to the cells in the body occur all the time. Changes happen to the genetic code in a cell, and it almost certainly dies. (A side question is : what exactly happens to a cell when it dies? Presumably some process or other ‘detects’ the death and breaks it up? Or does the first failure cause other processes to fail until the integrity of the cell is lost? Lots of questions). However, unless the failure is dramatic, explosion-like rather than simple deflation, it should not affect its neighbouring cells, should it? So in general the death of a single cell is probably not noticeable.

Going back to the computer program analogy, in a computer there are dozens, if not hundreds of programs running all the time, but the user is not aware of any other than the one he is interacting with. Equating cells with computer programs, it is most likely that a random change would cause a program or a cell to die, with little effect on the computer or body as a whole.

Facit computer memory
Facit computer memory (Photo credit: liftarn)

All the programs running in a computer need ‘memory’ to run in, and there is a limited supply of memory, so (conceptually at least) one program is given the task of managing the memory allocations. Damaging the memory manager program could theoretically lead to it repeatedly allocating memory until there was none free for allocation. The computer would, once again, crash. If a program is damaged in a particular way it could ask repeatedly for memory and again cause itself or other programs. or even the whole computer to crash.

In a living organism there does not seem to be a single equivalent of the ‘memory manager’ or ‘resource manager’. In a living organism everything seems to be done by consensus between cells. (That is both anthropomorphic and probably naive, but it will do, I think).

So, although I’d estimate that the vast majority of changes to the genetic code would result in cell death and nothing else, a very, very small number of changes could result in the cell soaking up as much of the cell-level resources as it can and damaging the cell itself, its neighbouring cells or the whole organism.

Genetic code
Genetic code (Photo credit: Martina Gobec)

That, however, is not cancer. For damage to result in a cancer it has to damage the cell in a particular way. In a computer, cancer would be analogous to a program continually creating copies of itself and using up all the system resources, which would result in the system crashing. Almost all cells have the ability to duplicate themselves, but whether or not they do replicate is, so far as I know, determined by the conditions in the cell itself and conditions in its environment, ie the surrounding cells, possibly signalled by chemicals or chemical gradients.

For a cell to become cancerous, it first of all must be inclined to duplicate itself and it would also have to be able to ignore any signals from its environment. The damage to the genetic structure to achieve this seems to me to be remarkably specific. Its like damaging a computer program in such a way as to destroy a control loop. Possible, but not very likely.

Main sites of metastases for some common cance...
Main sites of metastases for some common cancer types. Primary cancers are denoted by “…cancer” and their main metastasis sites are denoted by “…metastases”. List of included entries and references is found on main image page in Commons: (Photo credit: Wikipedia)

Then there is the issue of metastasis. This is how cancer spreads. It first of all attacks the boundary of the organ it is embedded in, then some cancer cells migrate into other organs. Interestingly, when they start to form a cancerous tumour in the new organ, they are still identifiable as cells from the original organ.

Think for a moment about what that means. A cancer which metastasizes has to have its genetic material damaged in such a way that it can do all of the following :

  • divide in an uncontrolled manner
  • attack the walls of the organ it is contained in
  • migrate to other organs (and it can be very specific about the organs it migrates to)
  • settle there and start to divide again

That’s a remarkably specific set of actions to occur as the result of damage. Damage usually results in less efficient operation, both of computer programs and bodies. Of course the damage doesn’t have to create these action ‘programs’ in the genetic material. They may be already there. All that the damage needs to do is somehow kick off those actions in sequence to cause the cancer to form and metastasize. To a programmer it would look like a small chunk of code to call those routines which I’ve called ‘actions’. The only other time in one’s life that one’s body experiences explosive growth and cell migration is in the womb and as a young child. One can imagine that damage could somehow kick off the genes or part of the genetic code that was used when one was a developing foetus.

foetus (Photo credit: Leo Reynolds)

This is easier to contemplate than damage which somehow creates the whole process from scratch. It does imply that the damaging agent somehow attacks a specific part of the genetic material and replaces it with some very specific other material that has the specific effect of kicking off explosive growth and metastasis.

I’m not geneticist or cancer specialist of course, so my musings above may be way, way off beam. They could be and probably are complete rubbish. I can’t and won’t defend them if anyone were to attack them. My main thesis is that it seems incredibly unlikely that damage to the genetic material could cause the specific effects of cancer, which are uncontrolled growth and metastasis.

Yet cancer happens and happens frequently and in varied ways. There are many sorts of cancer and they appear to be often triggered by specific stimuli. All my arguments above founder on that logical rock.

Shipwreck (Photo credit: Wikipedia)
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