ass cancer
Example:
Doctor: "you have ass cancer."
The Man Who Could Sit Anywhere: "ass cancer?!?!?"
Doctor: "it's uh... when you have cancer in your ass."
The Man Who Could Sit Anywhere: "oh my god, how could this happen?"
Doctor: "Think - have you been sitting anywhere radioactive lately?"
Doctor: "you have ass cancer."
The Man Who Could Sit Anywhere: "ass cancer?!?!?"
Doctor: "it's uh... when you have cancer in your ass."
The Man Who Could Sit Anywhere: "oh my god, how could this happen?"
Doctor: "Think - have you been sitting anywhere radioactive lately?"