10. Blood in the semen
This is a somewhat infrequent sign of prostate cancer, but when it occurs you should immediately see a doctor. Bloody semen can be caused by a variety of symptoms ranging from kidney stones scratching up the seminal vesicle, to tumorous growths in the prostate. Once you go to the doctor for this symptom, they will run a variety of tests to determine the exact cause of blood in the semen.