How can love and compassion affect cancer survival?

Quality of life. The old "pop"/"magic" claim that will-to-live or thinking-nice-things actually affected cancer growth is probably not true, but if a person is surrounded by good people, and has a chance to take care of one's last business, the quality of the survival will be better. Be kind, but not with the expectation of magic beyond improved relationships.
Quality of life. Love and compassion are not likely to change the survival rate but would improve the quality of life of the patient which is not a trivial consideration.