Sounds like the old "head in the sand" approach to dealing with cancer. I wish i could be like that, but i'm wayyyy too rooted in reality. I find some people like to talk about it, some want to just "think positive" (is that ignoring it?) and some friends have just FLED.
Basically, all i can say is that however he wants to deal with it, i think he should be able to. Try to remember that you love him (if you do) and that this might be his request from you. If you can, ignore it and have a good time with him. If it is driving you crazy, try to find a friend to dump on about it. And if it is driving you too crazy, tell him that you can't handle it anymore and you have to know or you walk. Then talk or walk.
I know i have gone thru a personality change. I'm having a hard time dealing with things unless I just shut off and go about my business. Then I can at least get thru the day. At night, I fluctuate from "what the hell, have another, I'm going to die anyway," to "I'm gonna beat this no matter what, let's make plans for 5 years from now."
If you love him, try to stick with him and process emotionally later. If not, then.... I don't know. This is one of the big mysteries of life. I haven't figured it out yet, if I ever do at all.