It could be a need for attention from people, maybe that person doesn't want to have cancer, but wants the attention (s)he can get from having it. However, if this person really wants to have cancer, then (s)he could have depression, suicidal thoughts or similar, the thing is that there are lots of ways to die and I'm not able to know why would someone preffer dying from a cancer. I don't know this person so I can't really say much.