You are performing a routine exam on a 70-year-old male. On exam of his prostate you palpate a mass that is 1cm in diameter, hard, and non-tender. The patient has had a 6-month history of fatigue. He denies weight loss or night sweats. What is your most likely diagnosis?

a) Benign prostatic hyperplasia
b) Internal hemorrhoid
c) Prostatitis
d) Prostate cancer