This is a medical question of type : stages 
 What are the stages of Anal Cancer ? 
 Key Points
                    - After anal cancer has been diagnosed, tests are done to find out if cancer cells have spread within the anus or to other parts of the body.     - There are three ways that cancer spreads in the body.    - Cancer may spread from where it began to other parts of the body.    - The following stages are used for anal cancer:         - Stage 0 (Carcinoma in Situ)     - Stage I     - Stage II     - Stage IIIA     - Stage IIIB     - Stage IV
                
                
                    After anal cancer has been diagnosed, tests are done to find out if cancer cells have spread within the anus or to other parts of the body.
                    The process used to find out if cancer has spread within the anus or to other parts of the body is called staging. The information gathered from the staging process determines the stage of the disease. It is important to know the stage in order to plan treatment. The following tests may be used in the staging process:          -   CT scan (CAT scan): A procedure that makes a series of detailed pictures of areas inside the body, such as the abdomen or chest, taken from different angles. The pictures are made by a computer linked to an x-ray machine. A dye may be injected into a vein or swallowed to help the organs or tissues show up more clearly. This procedure is also called computed tomography, computerized tomography, or computerized axial tomography. For anal cancer, a CT scan of the pelvis and abdomen may be done.    -   Chest x-ray : An x-ray of the organs and bones inside the chest. An x-ray is a type of energy beam that can go through the body and onto film, making a picture of areas inside the body.    -   MRI (magnetic resonance imaging): A procedure that uses a magnet, radio waves, and a computer to make a series of detailed pictures of areas inside the body. This procedure is also called nuclear magnetic resonance imaging (NMRI).    -   PET scan (positron emission tomography scan): A procedure to find malignant tumor cells in the body. A small amount of radioactive glucose (sugar) is injected into a vein. The PET scanner rotates around the body and makes a picture of where glucose is being used in the body. Malignant tumor cells show up brighter in the picture because they are more active and take up more glucose than normal cells do.
                
                
                    There are three ways that cancer spreads in the body.
                    Cancer can spread through tissue, the lymph system, and the blood:         - Tissue. The cancer spreads from where it began by growing into nearby areas.     - Lymph system. The cancer spreads from where it began by getting into the lymph system. The cancer travels through the lymph vessels to other parts of the body.     - Blood. The cancer spreads from where it began by getting into the blood. The cancer travels through the blood vessels to other parts of the body.
                
                
                    Cancer may spread from where it began to other parts of the body.
                    When cancer spreads to another part of the body, it is called metastasis. Cancer cells break away from where they began (the primary tumor) and travel through the lymph system or blood.         - Lymph system. The cancer gets into the lymph system, travels through the lymph vessels, and forms a tumor (metastatic tumor) in another part of the body.    - Blood. The cancer gets into the blood, travels through the blood vessels, and forms a tumor (metastatic tumor) in another part of the body.        The metastatic tumor is the same type of cancer as the primary tumor. For example, if anal cancer spreads to the lung, the cancer cells in the lung are actually anal cancer cells. The disease is metastatic anal cancer, not lung cancer.
                
                
                    The following stages are used for anal cancer:
                    Stage 0 (Carcinoma in Situ)    In stage 0, abnormal cells are found in the innermost lining of the anus. These abnormal cells may become cancer and spread into nearby normal tissue. Stage 0 is also called carcinoma in situ.        Stage I    In stage I, cancer has formed and the tumor is 2 centimeters or smaller.        Stage II    In stage II, the tumor is larger than 2 centimeters.        Stage IIIA     In stage IIIA, the tumor may be any size and has spread to either:            -  lymph nodes near the rectum; or      - nearby organs, such as the vagina, urethra, and bladder.              Stage IIIB    In stage IIIB, the tumor may be any size and has spread:            - to nearby organs and to lymph nodes near the rectum; or     - to lymph nodes on one side of the pelvis and/or groin, and may have spread to nearby organs; or     - to lymph nodes near the rectum and in the groin, and/or to lymph nodes on both sides of the pelvis and/or groin, and may have spread to nearby organs.              Stage IV    In stage IV, the tumor may be any size and cancer may have spread to lymph nodes or nearby organs and has spread to distant parts of the body.