as serious as cancer 

something extremely serious, like cancer

Brittany: Hey! I just crashed my car into a ditch!
Joe: Are you serious??
Brittany: As serious as cancer!

as serious as cancer by B Fox January 15, 2008

I'm as serious as dick cancer 

The term "I'm as serious as dick cancer" is a response from one guy when asked by another guy if they are serious.

Person 1- Are you serious????

Person 2- I'm serious, bro! I'm as serious as dick cancer"!

I'm as serious as dick cancer by Hankscolts November 13, 2011