Doc Cancer's love, Holly Winters had gained immortality through an experimental accident. He tried to deal with the fact that she would outlive but ultimately it drove him over the edge and he tried to recreate the experiment that gave her powers. Instead he turned into a huge mutated freak. Unable to deal with the emotional turmoil of not being worthy of Holly, he has become psychotically obsessive and will kill any man who even looks at her; Commander Capitalism made that mistake.