context: If the results of your prostate-specific antigen ( PSA) test or digital rectal exam ( DRE) suggest that you may have prostate cancer, your doctor will perform a biopsy to find out for sure. He'll insert a thin, a hollow needle through the wall of your rectum and remove about a dozen tiny pieces of prostate tissue. The procedure, which only takes about 10 minutes, may cause some discomfort, but not serious pain. Your doctor will send the tissue samples to a doctor called a pathologist, who will look at the cells under a microscope. If she finds cancer, she'll grade it using a method called the Gleason Scoring System. Cancer cells don't look the same as healthy cells. The more different they appear, the more aggressive the cancer tends to be. The Gleason system uses the numbers 1 to 5 to grade the most common (primary) and second most common (secondary) patterns of cells found in a tissue sample. Grade 1: The tissue looks very much like normal prostate cells. Grades 2-4: Cells that score lower look closest to normal and represent a less aggressive cancer. Those that score higher look the furthest from normal and will probably grow faster. Grade 5: Most cells look very different from normal. Doctors add your primary and secondary numbers together to form your total Gleason score. That tells you how aggressive the cancer is. The lowest score for a cancer is 6, which is a low-grade cancer. A Gleason score of 7 is a medium-grade cancer, and a score of 8, 9, or 10 is a high-grade cancer. Generally speaking, the higher your Gleason score, the more aggressive the cancer. That means it's more likely to grow and spread to other parts of your body. Doctors use this information, along with the stage of the cancer, to choose the best treatment for you. While the grade tells you how fast your cancer is growing, the stage lets you know how advanced the cancer is. Most doctors use the TNM staging system. It uses a number system to show how big the tumor is and how far the cancer has spread. TNM System T ( Tumor): The extent of the primary tumor is determined by describing its size and location. If the tumor can't be assessed, the stage is TX. If no tumor is found, the stage is T0. As the size and spread increase, so does the stage -- T1, T2, T3, or T4. In addition to the basic categories, doctors may use subcategories like T1a or T1b to add more description. N ( Nodes): This determines if the cancer has spread to the lymph nodes near your bladder. If the nodes can't be assessed, the stage is NX. If no nodes are affected, the stage is N0. If there is cancer in the nodes, a number is placed after the N (such as N1, N2, or N3) indicating the number, size and location of nearby lymph nodes involved. M ( Metastasis): The cancer has either spread to the bones or other organs ( M1) or hasn't ( M0). Doctors may also use subsets like M1a for distant lymph nodes or M1b for bones, or M1c for other sites. Doctors combine the T, N, and M results with the Gleason score (grade) and PSA level in a process called stage grouping. The overall stage is expressed in Roman numerals from I (the least advanced) to IV (the furthest along). Doctors use the stage to help determine the best course of treatment for you. Stage I The cancer is growing in your prostate, but hasn't yet spread beyond it. In most cases, the tumor can't be felt during a digital rectal exam ( DRE) or seen in imaging tests. The Gleason score is 6 or less and the PSA level is less than 10. The tumor is in one-half or less of only one side of the prostate. Stage IIA The cancer is growing in your prostate, but hasn't spread beyond it. The doctor may or may not be able to feel the tumor during a DRE or see it on an imaging test. The tumor can touch more than half of one lobe of the prostate but doesn't involve both lobes. The Gleason score is 7 or less and the PSA level is less than 20. Stage IIB The cancer is growing in the prostate, but hasn't spread beyond it. The doctor may or may not be able to feel the tumor during a DRE or see it on an imaging test. The tumor can be in one or both lobes of the prostate. The Gleason score is 7 and the PSA level is less than 20. Stage IIC The cancer hasn't spread beyond the prostate. The doctor may or may not be able to feel the tumor during a DRE or see it on an imaging test. The tumor can be in one or both lobes of the prostate. The Gleason score is 7 or 8 and the PSA level is less than 20. Stage IIIA The cancer has not spread outside the prostate. The doctor may or may not be able to feel the tumor during a DRE or see it on an imaging test. The cancer has not spread to any lymph nodes. The Gleason score is 8 or less and the PSA level is at least 20. Stage IIIB The cancer has spread outside the prostate but hasn't made it to the lymph nodes or to distant sites in the body. The Gleason score is 8 or less and the PSA is any level. Stage IIIC The cancer has or has not spread outside the prostate. The cancer has not spread to any lymph nodes. The Gleason score is 9 or 10 and the PSA is any level. Stage IV A The cancer has or has not spread to tissues outside the prostate. The cancer has spread to nearby lymph nodes, but not to distant sites in the body. The Gleason score and PSA are any value. Stage IV B The cancer has or has not spread to tissues or lymph nodes near the prostate. The cancer has spread to distant sites in the body such as lymph nodes, bones, or other organs. The Gleason score and PSA are any value.