system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why are advanced stage colon cancer patients expected to live only 21.4 months after diagnoses? What actually kills them? (What will actually casue my death?)
gpt
At later stages, the cancer spreads to other systems, such as your pancreas, lymph nodes, etc. The most common is the liver. 

What is bad is that most of these organs affect the entire body so once the cancer gets into that system, it can travel anywhere, like a freeway. Then it is just a case of how well those organs can function with cancer taking up space, pinching, cutting off blood supply, etc.

Good luck with treatment. Bring a good book to chemo, and be sure to buy Gatorade for at home. Half Gatorade, half water, and drink as much as you can stand.