Being mindful of your need for us to be scientific Gingernut, how are you going to find out if someone has cancer if you don't screen?
I had no symptoms, no pain, no inkling for years. A Doctor shocked by my PSA reading found no abnormality in a physical check, the specialist found no abnormality in his physical check, but the surgeon removed a tumour the size of an orange.
That's why you need both a physical and a PSA, neother are certain, but both together increase the odds of detection.