The region of the prostate gland anterior to the central and peripheral zones, surrounding the proximal urethra. It is the zone of the human prostate gland that grows the most throughout life, and is responsible for benign prostatic hypertrophy. [ http://www.ncbi.nlm.nih.gov/pubmed/30566875 https://orcid.org/0000-0002-7431-4139 ]