When a biopsy confirms the presence of cancer, the next step, called grading, is to determine how aggressive the cancer is. The most common cancer grading scale runs from 1 to 5, with 1 being the least aggressive form (tissue cells look normal). Known as the Gleason scores, these numbers (which refer to the appearance and activity of cancer cells) may be helpful in determining which treatment option is best. The Gleason score adds the grades of the 2 most prevalent patterns of cells. Therefore, scores may range from 2 (nonaggressive cancer) to 10 (very aggressive cancer). The eventual spread of the tumor is dependent on the aggressive nature of the prostate cancer cells.