I don’t know anyone who would rely on PSA testing as their sole source for a cancer diagnosis, but - depending on the results, especially comparing more than one test (i.e., PSA velocity) - it’s certainly a useful indicator for further investigation.
I agree. I'm a prostate cancer "survivor". First it was the finger up the bum, then a PSA, then a biopsy. Stage 1. Radiation.
Today (10 years later) I am sure there are CT scans etc. But for a starting point, the good old PSA does the trick. Ignorance of symptoms is not.