In the past, I’ve wondered whether lung cancer might be a product of the radioactive fallout from nuclear bomb tests. After thinking a bit more about radioactivity last weekend, I got to wonder what happened when a speck of radioactive material, spitting alpha and beta particles in all directions, got lodged in human body tissue.
I’ve read several times that when, this happens, it invariably causes cancer, by (as seems to be believed) mutating cell DNA. But as I saw it, most likely what happens is that, rather than having their DNA mutated, cells near the source of radioactivity are simply killed. And this creates voids in the tissue, into which adjacent living cells can reproduce.
For it seems to me that if a cell is going to grow and divide, it needs to have the space to do so. So if a cell is completely surrounded by other cells, it can’t grow and divide. It’s only when a space adjacent to it appears – as when an adjacent cell is killed by radioactivity -, that it can grow and divide.
It also seemed reasonable for daughter cells to vary slightly from their parents, and have slightly different reproduction rates than their parent cells – if only because in human bodies some cells (e.g. skin or gut cells) reproduce more rapidly than those in other tissues. Equally, cancer cells – which started life as human cells – usually reproduce even more rapidly still.
Using these simple rules, I set about building a computer simulation model. In it I constructed a grid of 100 x 100 cells, all with the same reproduction time – 20 hours -. These cells could only grow and divide if there was an empty space next to them. And because there were no voids for them to grow into, initially no reproduction took place.
I then introduced a “radioactive source” in the middle of the grid, which randomly killed off cells around it, according to an inverse-square rule. At which point adjacent cells started to grow and divide. I sat back and watched what happened.
Initially (see 1 at right), a (white) void appeared around the radioactive source, with yellow cells – with roughly 20 hour reproduction times – all round it.
And then, after 15,000 hours, green cells – with 15 hour reproduction times – started appearing (2) in small numbers, mostly fairly near the central void. These gradually grew in numbers (3).
And then blue cells with 10 hour reproduction times began to appear, and gradually grew more numerous (4).
And then, after 37,000 hours, purple cells with 5 hour reproduction times appeared (5), and began to fill the central void (6). They were reproducing more rapidly than the radioactive source could kill them off.
Finally the fastest reproducing red cells appeared, with 1 hour reproduction times (7).
Thereafter the roughly circular patch of cells got slowly bigger and bigger, until it was nearly touching the edge of the cell grid after 56,000 hours (10).
After that, I tried several other runs, with very similar results.
Initially when I tried this, I gave daughter cells an equal chance of being faster or slower reproducing than their parent cell. But the faster growing cells came to predominate so rapidly that I instead arranged that daughter cells only had a 10% chance of being faster, a 40% chance of being the same, and a 50% chance of being slower reproducing than their parent cell. So the results shown are from a model that is quite heavily weighted in favour of slower-reproducing daughter cells. Despite this, the fastest-reproducing cells came to predominate.
In this manner I’d managed to simulate what very much looked like a cancer tumour made up of fast-reproducing cells. But these rapidly-reproducing cells had been generated by a process of natural selection that favoured the fast-reproducing cells that were (usually) quickest off the mark to fill an adjacent space.
But in some ways, the most important thing was for there to be voids into which cells could grow and divide. If there were no voids, growth and reproduction stopped dead. Just having fast-reproducing cancer cells wasn’t enough: there also need to paths (voids) down which such cells could propagate.
In this case, the radioactive source was continually creating voids, by killing off cells around it, mostly very close to it, but also to a lesser extent further away.
In a previous (very different) model, I argued that as people aged, their cells reproduced more and more slowly. And when this happens, dead cells are replaced more and more slowly from the surrounding tissue. And this would mean that in old people, there may often be lots of small voids throughout the body, which are ideal for fast-reproducing cancer cells to colonise. And so old people are perhaps more prone to cancer for this reason.
And if the tissues of old people are full of voids, then this may explain why they get smaller, with sunken cheeks, and get covered in wrinkles as their skin becomes wrapped around a shrinking body.
And if young people usually don’t get cancer, it’s probably because their cells are reproducing more rapidly, and quickly fill any voids that appear, and so cancer usually can’t get a grip.
If this is how cancer develops, then all that’s needed to trigger it is something that kills off cells in large enough numbers to create the voids into which cells can grow and divide more and more rapidly. It needn’t be radioactivity that does this. It might also happen when someone develops some wasting disease that kills off lots of body cells, without actually killing them. It might also come from physical injuries which leave unfilled voids in a body.
Equally, if a growing tumour exerts an outward force on tissues around it, this might sometimes rupture the tissue, and create cracks or splits along which cancer cells can propagate.
It might also be that, when something is described as “carcinogenic”, it’s simply something that will kill cells when left in contact with them for long enough. A pellet of cyanide (or any number of other compounds) placed in human tissue might have the same effect as a speck of radioactive material, as it gradually poisons cells around it.
Needless to say, it’s very unlikely that smoking or drinking or eating anything would kill off cells in sufficient numbers to create the necessary voids.
And this also suggests that current treatments of cancer – with radioactivity, for example – may be counterproductive, because while they may succeed in killing off cancerous tumours, they may as a result also leave voids into which cells may subsequently grow and divide, causing entirely new cancers.
Anyway, this was a very simple computer model (it only took an evening to write it), but its results seemed promising enough to suggest further study/development.