A cancer patient, usually abbreviated as "CP", refers to someone that puts in more than sufficient effort. It's a more derogatory form of the word "tryhard".
Its reasoning is that cancer patients in real life have to try very hard to overcome their cancer.
Why are we losing this game?

Because we're playing against absolute cancer patients.
by Partisan Passers-By Proxy March 15, 2016
A person who is toxic, cancerous and an ass. Not to be confused with actual cancer victims
by Autistic dude November 8, 2019
when a guy ejaculates in a girls hair and it gets so hard to get out the girl must shave her head, kind of like getting gum in one's hair.
my girl has to shave her head

why?

bc i came in her hair and she cant get it out

ohh the cancer patient. that is funny
by olko March 30, 2009
The ultimate fucking cancer-carrying diseased shithead. Needs high amounts of gamma radiation to cure usually resulting in death. Not to be confused with a person who actually has cancer.
Kid: Hey, do u wanna play minecraft, dad?
Dad: You useless fuckin cancer patient
by Seeker of Truth-- November 19, 2015
A little cunt ass bitch that looks like a 4 ft tall banana lookin ass cunt bitch boy and sells his man pussy for money for his cocane addiction (he’s gay too)
What a funny lookin cancer patient lookin ass

you got there fella
by Boiiwantthisusername December 4, 2017