A biopsy is an outpatient operation in which your doctor utilises ultrasound guidance to puncture your prostate with a needle 12 to 20 times, extracting a sample of tissue from each stab. The samples are submitted to a lab, where a pathologist examines the tissue and assesses whether the cells are malignant and how aggressive they are depending on how they seem. Because only a representative sample from each part of your prostate is taken, the test isn't perfect. If there is cancer, one or more of the sticks may detect it — or none at all. Negative test results are not always indicative of the absence of cancer, but they are certainly hopeful.