How cancer starts: how a normal cell turns into cancer
Cell division: the rules that stop your cells from copying too much
Your body makes about four million new cells every second, each one a copy of an older cell. So why does nothing grow out of control, and what is different when something does?
-
1
Rono has had the same small mole on his shoulder for fifty years. This Sunday, at the town pool where you swim together, you see that it has grown, and its edge is uneven.
-
2
Rono shows it to his skin doctor, Miva. She explains that a mole is a small family of pigment cells, the cells that give skin its color. Most moles stop growing and never cause trouble. This one had stopped too, until now.
-
3
To see why, look inside the skin. It is made of cells packed side by side, like every part of you. Your body has about 30 trillion of them.
-
4
Cells wear out, so your body makes new ones. A cell copies itself and splits in two. This is cell division. Your body does it about four million times every second, mostly to make new blood cells.
-
5
With so much copying, there are rules. The first one: a cell does not split when it likes. It waits until other cells send a chemical message that says "copy now".
-
6
The second rule: when cells touch on all sides, they stop. A gap fills up, and the copying ends there.
-
7
The third rule: a cell that is badly damaged destroys itself, quietly, so it cannot make broken copies.
-
8
Cancer starts when one of your own cells stops following these rules. It copies with no message. It does not stop when it touches its neighbours. It does not destroy itself when it is damaged. And every copy breaks the rules too.
-
9
Rono's mole began with one pigment cell, when he was a young man. That cell broke the first rule for a while: it copied with no message, into a small mole. Then the family stopped growing, and a mole that stops is not cancer. What changed in that first cell was tiny: one letter of its DNA.
-
Quick check
A cut that heals flat.
Show the answer
The new cells touch the cells around them on all sides, and cells that touch stop copying. The messages that said "copy now" also stop once the cut is closed.
-
Go further
Two names for the rules you saw.