The doctor may order other exams, including ultrasound and x-rays, to learn more about the cause of the symptoms. But to confirm the presence of cancer, doctors must perform a biopsy. During a biopsy, the doctor uses needles to remove small tissue samples from the prostate and then looks at the samples under a microscope.  If a biopsy shows that cancer is present, the doctor will report on the grade of the tumor. Doctors describe a tumor as low, medium, or high-grade cancer, based on the way it appears under the microscope.