jmadrid, the majority--but not all--studies conclude that a targeted + systematic biopsy misses less cancer than a target-only one based on a MRI. While both a biopsy and an MRI can miss exisiting cancer, any MRI has a limit of resolution, whereas a random core can get lucky and sample a tiny lesion that didn't show up on imaging. If I remember correctly, the chances of this happening are about
5-8%. It's a small, but not insignificant, gain.
One study put the ideal number of cores to take per MRI-identified target at 2-3 (sufficient to ensure the target will be sampled without excess cores). My takeaway from all this is that for a "standard" (non-saturated) biopsy, the total number of cores if there are, for example, 1 MRI-identified target in each of 2 prostate zones would be 4-6 cores for the targets plus 1 core in each of the remaining 10 zones, for a total of 14-16 cores. Frankly, you are lying there on the table, presenting your butt to your uro. You have no place to hide; the jig is up. You may as well have all prostate zones sampled. Don't skimp
Djin