A 50 year old male attends your general practice clinic with some problems passing water for the past two weeks. He tells you that he is finding it difficult to maintain a stream and sometimes experiences some dribbling. He had a few episodes of mild dysuria three days ago, which has now subsided. He has not had a fever, haematuria, foul smelling urine, nocturia or noticed his urine being cloudy. What is your top differential?