Most prostate cancers originate in the peripheral zone of the prostate gland. Symptoms typically manifest only when the tumor has grown sufficiently to exert pressure on the urethra. Consequently, prostate cancer often remains asymptomatic in its early stages. When symptoms do occur, they may include difficulty initiating urination, a weak or interrupted urine stream, increased urinary frequency (especially at night), blood in the urine or semen, erectile dysfunction, painful ejaculation, unexplained weight loss, persistent fatigue, and bone pain (e.g., in the back, hips, or ribs), which can indicate advanced disease.