This is a medical question of type : stages 
 What are the stages of Childhood Non-Hodgkin Lymphoma ? 
 Key Points
                    - After childhood non-Hodgkin lymphoma has been diagnosed, tests are done to find out if cancer cells have spread within the lymph system or to other parts of the body.     - There are three ways that cancer spreads in the body.    - The following stages are used for childhood non-Hodgkin lymphoma:         - Stage I     - Stage II     - Stage III     - Stage IV
                
                
                    After childhood non-Hodgkin lymphoma has been diagnosed, tests are done to find out if cancer cells have spread within the lymph system or to other parts of the body.
                    The process used to find out if cancer has spread within the lymph system or to other parts of the body is called staging. The results of tests and procedures used to diagnose non-Hodgkin lymphoma may also be used for staging. See the General Information section for a description of these tests and procedures. 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 procedure also may be used to determine the stage:         -   Bone scan : A procedure to check if there are rapidly dividing cells, such as cancer cells, in the bone. A very small amount of radioactive material is injected into a vein and travels through the bloodstream. The radioactive material collects in the bones with cancer and is detected by a scanner.
                
                
                    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.
                
                
                    The following stages are used for childhood non-Hodgkin lymphoma:
                    Stage I     In stage I childhood non-Hodgkin lymphoma, cancer is found:            - in one group of lymph nodes; or     - in one area outside the lymph nodes.           No cancer is found in the abdomen or mediastinum (area between the lungs).       Stage II     In stage II childhood non-Hodgkin lymphoma, cancer is found:            - in one area outside the lymph nodes and in nearby lymph nodes; or     - in two or more areas either above or below the diaphragm, and may have spread to nearby lymph nodes; or     - to have started in the stomach or intestines and can be completely removed by surgery. Cancer may have spread to certain nearby lymph nodes.              Stage III     In stage III childhood non-Hodgkin lymphoma, cancer is found:            - in at least one area above the diaphragm and in at least one area below the diaphragm; or     - to have started in the chest; or     - to have started in the abdomen and spread throughout the abdomen; or     - in the area around the spine.              Stage IV     In stage IV childhood non-Hodgkin lymphoma, cancer is found in the bone marrow, brain, or cerebrospinal fluid. Cancer may also be found in other parts of the body.