This is a medical question of type : stages 
 What are the stages of Melanoma ? 
 Key Points
                    - After melanoma has been diagnosed, tests are done to find out if cancer cells have spread within the skin 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 method used to stage melanoma is based mainly on the thickness of the tumor and whether cancer has spread to lymph nodes or other parts of the body.    - The following stages are used for melanoma:         - Stage 0 (Melanoma in Situ)      - Stage I     - Stage II      - Stage III      - Stage IV
                
                
                    After melanoma has been diagnosed, tests are done to find out if cancer cells have spread within the skin or to other parts of the body.
                    The process used to find out whether cancer has spread within the skin 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 and procedures may be used in the staging process:         -   Physical exam and history : An exam of the body to check general signs of health, including checking for signs of disease, such as lumps or anything else that seems unusual. A history of the patients health habits and past illnesses and treatments will also be taken.    -   Lymph node mapping and sentinel lymph node biopsy : Procedures in which a radioactive substance and/or blue dye is injected near the tumor. The substance or dye flows through lymph ducts to the sentinel node or nodes (the first lymph node or nodes where cancer cells are likely to spread). The surgeon removes only the nodes with the radioactive substance or dye. A pathologist views a sample of tissue under a microscope to check for cancer cells. If no cancer cells are found, it may not be necessary to remove more nodes.     -   CT scan (CAT scan): A procedure that makes a series of detailed pictures of areas inside the body 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 melanoma, pictures may be taken of the chest, abdomen, and pelvis.    -   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.    -   MRI (magnetic resonance imaging) with gadolinium : A procedure that uses a magnet, radio waves, and a computer to make a series of detailed pictures of areas inside the body, such as the brain. A substance called gadolinium is injected into a vein. The gadolinium collects around the cancer cells so they show up brighter in the picture. This procedure is also called nuclear magnetic resonance imaging (NMRI).    -   Blood chemistry studies : A procedure in which a blood sample is checked to measure the amounts of certain substances released into the blood by organs and tissues in the body. For melanoma, the blood is checked for an enzyme called lactate dehydrogenase (LDH). LDH levels that are higher than normal may be a sign of melanoma.        The results of these tests are viewed together with the results of the tumor biopsy to find out the stage of the melanoma.
                
                
                    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 melanoma spreads to the lung, the cancer cells in the lung are actually melanoma cells. The disease is metastatic melanoma, not lung cancer.
                
                
                    The method used to stage melanoma is based mainly on the thickness of the tumor and whether cancer has spread to lymph nodes or other parts of the body.
                    The staging of melanoma depends on the following:         - The thickness of the tumor. The thickness is described using the Breslow scale.    -  Whether the tumor is ulcerated (has broken through the skin).    - Whether the tumor has spread to the lymph nodes and if the lymph nodes are joined together (matted).    - Whether the tumor has spread to other parts of the body.
                
                
                    The following stages are used for melanoma:
                    Stage 0 (Melanoma in Situ)      In stage 0, abnormal melanocytes are found in the epidermis. These abnormal melanocytes may become cancer and spread into nearby normal tissue. Stage 0 is also called melanoma in situ.        Stage I      In stage I, cancer has formed. Stage I is divided into stages IA and IB.            -  Stage IA: In stage IA, the tumor is not more than 1 millimeter thick, with no ulceration.     -  Stage IB: In stage IB, the tumor is either:                   -  not more than 1 millimeter thick and it has ulceration; or       -  more than 1 but not more than 2 millimeters thick, with no ulceration.                          Stage II       Stage II is divided into stages IIA, IIB, and IIC.            -  Stage IIA: In stage IIA, the tumor is either:                   - more than 1 but not more than 2 millimeters thick, with ulceration; or       - more than 2 but not more than 4 millimeters thick, with no ulceration.                  -  Stage IIB: In stage IIB, the tumor is either:                   - more than 2 but not more than 4 millimeters thick, with ulceration; or       - more than 4 millimeters thick, with no ulceration.                 -  Stage IIC: In stage IIC, the tumor is more than 4 millimeters thick, with ulceration.               Stage III      In stage III, the tumor may be any thickness, with or without ulceration. One or more of the following is true:             -  Cancer has spread to one or more lymph nodes.     - Lymph nodes are joined together (matted).     - Cancer is in a lymph vessel between the primary tumor and nearby lymph nodes. The cancer is more than 2 centimeters away from the primary tumor.     - Very small tumors are found on or under the skin, not more than 2 centimeters away from the primary tumor.              Stage IV      In stage IV, the cancer has spread to other places in the body, such as the lung, liver, brain, bone, soft tissue, or gastrointestinal (GI) tract. Cancer may have spread to places in the skin far away from where it first started.