Doctors predict the course of a man's prostate cancer and select appropriate treatment based on the staging and grading of the tumor, information provided largely by laboratory pathologists, Gustavo de la Roza, MD, explains in this HealthLink on Air interview. The cellular anatomy and structure in a tissue sample reveal a histologic grade, which tells the aggressiveness of the cancer. Staging is a number that reveals whether the cancer has spread, and how far. Clinical staging accomplishes this through use of imaging studies. Pathological staging relies on the examination of tissue.