Eli5- Why does cancer predominantly affect organs rather than muscle?

Question

Why do you never hear of someone with calf cancer or bicep cancer but rather cancer affecting the organs or blood?

In: 287

Answer 1

You have many different kinds of cells in your body. They specialize in different jobs:
– some become blood cells
– some become brain cells (neurons)
– some become muscle cells
– some become antibody (immune system) cells

There are lots of types. Now, each type comes with their own blueprint/instructions to follow and for the most part, they follow those instructions to a T. They tell the cell everything,.from when, how, where to grow, to when to split/reproduce and even, when to die (there are lots of nuances to this, but ELI5).

Cancer as a gross oversimplification is when these instructions go wrong to such a degree that the cell is no longer following a set of instructions that are normal. On any given day, this is happening to millions of your cells inside your body (out of the billions of healthy ones). But in 99% of those cases usually, the bad instructions result in the cell following them to it’s doom. I.e. the bad instructions result in the death of the cell.

But in rare situations, the signal to die is ignored or doesn’t exist anymore and usually the “hey, time to reproduce” signal goes nuts and thus, the cell does what it is told to do, go nuts and reproduce.

Now, here’s the thing: this can happen in ANY kind of cell in your body whatsoever.

So back to your question: let’s say, I pick a cell type that’s capable of rapid reproduction/splitting and I give it a set of instructions that tell it to not die (and none of its children will naturally either) and to reproduce like crazy. It’ll do exactly that, wherever it happens to be in the body. And because it can reproduce fast, it can get damaging (think of a lump growing in a critical artery) before you even know it’s there.

Now, that can happen too in say, a muscle cell, but because it is either an extremely slow reproducer OR doesn’t reproduce at all, it becoming cancerous just isn’t the same danger because even if it was, it would take so long to grow into something dangerous that you’ve most likely died of some other cause. Also note that your immune system regularly spots and destroys cancerous cells too.

Remember, everyone has cancer, all the time. It’s a normal consequence of every cell having their own instructions without a safe ‘gold record to compare it against’. We only call cancer out as a condition when it becomes detectable as something that will kill you quicker than other things.