What is the ruling on saying "cancer warrior"?

There is no harm in describing as "cancer fighter" anyone who resists the disease through treatment and having good expectations of Allah, or a doctor skilled in its treatment, or one who assists patients with it financially or morally. The intent of this description is to resist the disease and not surrender to it, which is a permissible matter. It has been stated in the Hadith: "Seek treatment, for Allah Almighty has not created a disease without also creating a cure for it, except for one disease: old age."