How do you detect Cancer?

I really am bemused by this disease, it makes human suffer so much and yet we are pondering about its cause? My uncle died of lungs cancer whereas he never smoked a single cigerrate or drinked or never indulged himself in any sort of such activities. My friend's mother died of oral cancer and she never in her life tasted tobacco. The people who die of cancer suffer immensly and die a painful death. I wonder when shall we be able to fight with this deadly disease and w'd be able to identify the cause of it? Any medical explanations?