Mal here is an interesting play on numbers. I remember reading somewhere or other that the average human body contains 50,000,000,000,000 (fifty trillion) cells. If you assume the average man is 90 kg he would have a volume of 90,000 ccs (given that human tissue is approximately as dense as water). Essentially this means that each CC of tissue contains 555,555,555 cells (lets round it out to 500 million)
If one PCa cell was left behind (invisible to the surgeon of course), with a really fast dividing (doubling) time of only one month, it sure is going to take a hell of a lot of months before there is even evidence that surgery failed ---- 20 months of doubling will get you to 1 million cells while 25 months will hit the 30 odd million mark. Gleason grade 4 cells have an average PSA output of 2ng/dL per CC so that 30 million cells will produce 0.1 ng/dL psa (now classed as detectable).
I do like to play with numbers but I really need to get a life!