Genetic tests are performed on urine samples and on prostateThe prostate is a walnut-sized gland located between the bla... Full Definition tissue removed during a biopsyAn examination of tissue removed from the body to understand... Full Definition or surgery. These tests look for genetic markers that tell doctors what genetic mutations are driving the cancerCancer is a group of diseases where cells grow abnormally an... Full Definition. Gene mutations cause cellular machinery to work incorrectly, typically causing cells to live when they should die or to reproduce much faster than normal cells. A look at the genes driving the cancer can help doctors tell if the cancer is aggressive or not.