Urology of Virginia mentions prostatic external or internal massage therapy as an alternative therapy practiced for medical or therapeutic reasons. Not only this improved urinary flow, increasing blood flow, it as well is part of maintaining the integrity of the prostatic tissue. External prostate massage may reduce pain, ease urination and enhance erection.
There is lots of anecdotal evidence for prostatic massage rather than large studies as such to this date.
Source:
Urology of Virginia, "What is Prostate Massage Therapy? - ProstateCancer911"