How do you gently tell a cancer male there is no chance of a relationship. Ever?

Just because he has cancer doesnt mean you cant be straight with him although it does mean you cant be rude as you wouldnt too anyone. But if you dont have feelings for him and you dont want a relationship just meet up with him and tell him that and you are sorry you dont feel the same way, you cant force yourself too like him. And if you did anyway it would be cruel. Take him out and introduce him too someone. Or just stay as good friends as possible if he wants too.