That is right. It is possible that these stats come from trials where their cut off is PSA 0.5. There studies, as well as the experience of oncologists that when the PSA goes below 0.2 or even 0.1, it is very much different. The scientific explanation is that at that level, very few malignant cells remain, if at all. The important point is it stays stable at that level. So regular monitoring is needed to make sure. I hope that helps.
Dont mind me. I am just another layman trying to make some sense of the hole thing.