A 55 year-old cisgender male patient comes to the primary care office for a general physical examination. He has had some lower back pain but denies change in bowel habits or rectal bleeding. His examination is unremarkable except for a digital rectal examination notable for irregular, asymmetric, hard nodule on the otherwise smooth posterior surface of the prostate. Examination of the scrotum and penis are normal. What disorder of the anus, rectum, or prostate is the most likely cause of these findings?