A study from the University of California of 3500 men who underwent radical prostatectomy for localised prostate cancer has shown that there is a risk of later cancer recurrence if the margins are "close". If there is less than 1mm of non-cancer tissue beween the cancer and where the surgeon cut, the risk of a later rise in PSA (indicating cancer recurrence) is 51% higher than if the margins were greater. This study was presented at the American Urological Association Annual Meeting in San Diego in May.
The following link takes you to an article outlining the study results:
AUA 2013: Study: Close surgical margins at radical prostatectomy