Atheism teaches that there is/was no creator. So if you're an atheist you're forced to conclude that cancer and death are just naturally what happens along with abiogenesis.
Yes, they are natural processes. Just like many other diseases we have figured out how to cure. Smallpox, polio, all those covered by antibiotics, etc. Yes, cancer is a scourge, but we are making progress. Many types of cancer (it isn't a single disease) already have treatments that work most of the time.
But these treatments didn't happen because people were praying. They happened because people were looking at the natural world, learning how it works, have doing the hard job of figuring out how to better this world rather than pining for the next.
So, while they are 'natural', they can also be fought with 'natural' methods and we can learn these methods by studying the natural world.