system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What cancer patients actually die of?

Is it blood being diverted from organs into the tumor? Weight of the tumor pressing down on the organs? Or something else?
gpt
Cancer kills the patient by causing the organs the stop working as they should. Cancer can be thought of as "out of control" cell growth. It overcrowds or overtakes organs causing them to not work right. When certain organs don't work like they should then it eventually causes death. E.g. Lung cancer causes the lungs to take in less oxygen which eventually causes the patient to weaken which can lead to other organs failing as they compete for oxygen and other resources. 

Cancer is actually very normal and we have these "out of control" cell growths all the time but most of the time our bodies can deal with it by killing these bad cells before they become too many or convert other cells from other organs to join in the rebellion. So, you can think of your body like a house with lots of children and these children all have chores. If one of these children is bad and isn't disciplined then he might make messes rather than do his chores. He may eventually talk his brothers and sisters to stop doing their chores but eventually if everyone breaks all the rules and don't do their chores the house eventually will fall part! This is why mommy and daddy want you to obey the rules and do your chores.