According to The Official Handbook of the Marvel Universe (1989) the guy exposed himself to radiation in order to gain super powers. In one rare realistic twist for Marvel Comics, he just contracted skin cancer instead. Reality soon went down the drain when the guy just created himself a skintight costume in order to inhibit the effects of the skin cancer eating away at his body. Since « not dying from his skin cancer » is a real badass super power, he became a super villain.
PICTURED: Dr Demonicus not dying.
Reality check: The guy still has cancer, which can still spread, attacking the rest of his body. What good is a costume that prevents you from dying from skin cancer when you have lung, colon, prostate and pancreas cancer?