Biopsy. A biopsy is the removal of a small amount of tissue for examination under a microscope. In recent years, doctors have learned it is helpful to have a larger tumor sample in order to determine the subtype of NSCLC and to do additional molecular testing (see below). If not enough of the tumor is removed to do these tests, another biopsy may be needed. A pathologist then analyzes the sample(s). A pathologist is a doctor who specializes in interpreting laboratory tests and evaluating cells, tissues, and organs to diagnose disease.