Cancer is really interesting. It's when your body's cells become so gifted that they won't stop growing, they forget what death is and they want to tell your whole body about it.
Sadly your body is but a line in Flatland, and doesn't get the concept of "just keep gowing and don't die".
And the cells over grow you, your body can't keep up with that rithm and starts shutting down.
Sometimes your body just beats the bad cells. Some other times it doesn't.
It's terrible when the cells win the battle.