I do agree with StephN and would like to add;
Being positive could give our bodies some hormone that will produce immune for lives.
I am thinking of myself after one or two hours in gym, there was a feeling of being able to fly, being able to smile even with a dog barking fiercely.
To fight cancer, we intake lot and lot of poison ... leads to weaker body system. Now it's a question of which system could be stronger between your mind with great attitude VS your body with poison cocktails.
"Light up your face with gladness
Hide every trace of sadness
Although a tear may be ever so near
That's the time you must keep on trying
Smile, what's the use of crying?
You'll find that life is still worthwhile
If you just smile"
Gift (with smiling)