Laboratory tests are measurements. All measurements have error. The error determines the detection limit. There is no such thing as a zero PSA. A PSA of < 0.05 ng/mL does not mean PSA is there but it is < 0.05 ng/mL, nor does it mean there is no PSA there. It means that if there is PSA there, then it is below the sensitivity of this assay, but it does not mean zero. No test can get to a measurement of zero anything. It can only provide limits of detection.

A "cure" is when the cancerous tissue now resides in a jar. Surgery is the best bet for a cure, particularly if it turns out the pathologist can step-section the entire prostate and report that the cancer is confined to the prostate. But even that might not give you a "zero" PSA. The typical guy choosing surgery would like to retain most erectile function, which means following Walsh's pioneering "nerve sparing" prostatectomy. But, in sparing nerves, a small amount of prostate tissue might unavoidably be left behind. In such a case, you might expect some PSA to still be present in the system. Note also, pathologists are humans making judgements or measurements. In other words, there are a whole series of measurements and judgements from first suspicion to definitive treatment. This is the art and science of medicine.

One last comment. We are close to being able to say: "Well, the bad news is you have prostate cancer; the good news is you won't die of prostate cancer". [given your age, overall health, co-morbidities, etc,]. Such a statement might allay some of this angst in this discussion. When my urologist told me those very words, I assumed that he was looking at my Gleason 9's and saying that because he was doing an internal calculation on whether I would die of something else long before the cancer became clinically evident.