A "positive attitude" can't be mandated from without. It can only come from within. I love the philosopher Victor Frankel, who was in a concentration camp. He believed that the one thing no one can take away from you is your own approach. Cancer and all ill health is a kind of suffering--like any problem such as divorce, widowhood, family issues, financial stress, frail aging, etc. etc. I am only 6 months into a cancer diagnosis--and have been told my prognosis is poor. I can't change any of that by a falsely positive "attitude." However, I can aim to have a very nice day, which might be a pleasant week, a good month, a fine year. Creativity is a wonderful support. Writing a diary, drawing, dancing--all of it helps. Of course friends and family are there not just for "support" but for intimacy and friendliness. Try walking in nature. I personally find talk therapy helpful, and all spiritual approaches, from meditation to prayer. But try to find your own path. I know folks who really benefit from gardening or knitting--or doing things for others (a capacity we don't lose). I've been disabled my entire adult life--so have a skill set around appreciating small things. A sick person and even a dying person can have a lot of joy. My main approach is to welcome those good moments and build on them.