A 68-year-old man presents with lower urinary tract symptoms (LUTS) of 6 months' duration. Digital rectal examination reveals a hard, irregular prostate with loss of the median sulcus. PSA is 12 ng/mL (normal <4). Transrectal ultrasound-guided prostate biopsy shows adenocarcinoma with a Gleason score of 8 (4+4). Staging workup including pelvic MRI and bone scan shows no evidence of metastatic disease. What is the most appropriate next step in management?