Cancer is caused by cancer cells, cells that are faulty and can't stop diving. The cancer cells cause the nearby tissues to die because they overcrowd the space and use up all the oxygen and glucose. Eventually if the cells are able to spread they would cause organ failure.
I try to make every day count because one day I will die like everyone else. No human I'm aware of has lived past 150 years of age. Even if it was normal to live beyond 200 years, that isn't a long time.