PSA density can be more relevant than the PSA number itself, because a large gland naturally produces more PSA.
The density is calculated by dividing the PSA reading (3.7) by gland size (53) to give the density of .069
Density of less than 1.5 is usually regarded as favourable.
Some research by Johns Hopkins into "insignificant" cancers uses this as one aspect when they discuss stage T1c cancer found in one or two cores, makes up less than half of each core, gleason score is 6 or lower, PSA density is less than .1 - .15 and the free PSA is greater than 15%
Johns Hopkins newsletters are at www.urology.jhu.edu/newsletters
The books by Lee Nelson and by Dr Peter Scardino cover these aspects in more detail.