Cancer of the ass, usually caused by sitting on your ass for long periods of time. Many RuneScape nerds get this type of cancer and need chemotherapy. People known with ass cancer: Telmomarques, No Excuses, Fredmcgarry, and Rens.
Ass cancer stages:
Stage 1 - Wanting to not get up from your chair for days
Stage 2 - Twitching of the gluteus maximus
Stage 3 - Black hole appears inside of the anus and sucks in all organs causing the person to die in a matter of seconds.
Did you hear about Telmomarques getting 120 dungeoneering?
Yeah, sadly he developed stage 3 of ass cancer.