system
Given the following post, respond as if you're commenting on Reddit:
human
[DC] The Joker is diagnosed with cancer. How does he react?

Is he upset? Does he find it funny? Does he accept his fate or does he seek treatment? How would he go about a doctor’s visit? Would he cooperate or would he end up killing anyone who tries to help him?
gpt
This happened in comics! "Joker: Last Laugh" has the Joker diagnosed with terminal brain cancer (inaccurately). He doesn't seem scared or upset, but he does proceed to create a new version of Joker Toxin that would be released into the weather and turn everyone into joker-clones, try to kill the president, have an army of supervillians spread havoc and very nearly push Nightwing into killing him.   
While not cancer, and debatably "real", on learning he was dying in "The Batman Who Laughs", Joker wipes out the entire batman's rogues gallery, burns down Gotham and releases a neurotoxin that turns batman evil when he kills him. 

So something like that happens. The joker isn't scared of death *per se*, but he doesn't want to go out quietly. If he's dying, he'll do something big and horrific, and likely try and bush batman into finishing the job. He'll accept his fate, but he'll want to go out doing something the world will *never* forget.