John, a 66-year-old man, reports to his physician that he has had trouble urinating for the last several months, with narrowed stream and difficulty...

John, a 66-year-old man, reports to his physician that he has had trouble urinating for the last several months, with narrowed stream and difficulty initiating urination. For the last 2 days. un- nation has become painful and produces only small amounts of urine. Urinalysis results are Within nor- mal limits. with the exception of the presence of bacteria on culturing. The following observations and lab tests are recorded in John’s chart: Digital rectal exam: enlarged prostate and pro- static nodule in one lobe Transrectal ultrasonography: abnormal mass present Urine culture: bacteria present Prostate-specific antigen: 12 ng/ ml What is the likely diagnosis? Why is it difficult for John to urinate?