Rapid Cancer does not exist. Now granted, there are 3 types of cancer. There's types that don't move or grow much at all(never require treatment), then, there's Slow Cancer, which can be detected, but usually doesn't impact you. Aggressive Cancer is a real problem, but Pretztail can't be diagnosed with nor can develop any type of cancer, because I'll reitterate: HE'S A LIVING PINATA.