What are the stages of Retinoblastoma ? 

Key Points
                    - After retinoblastoma has been diagnosed, tests are done to find out if cancer cells have spread within the eye or to other parts of the body.     - The International Retinoblastoma Staging System (IRSS) may be used for staging retinoblastoma.          - Stage 0     - Stage I     - Stage II     - Stage III     - Stage IV        - There are three ways that cancer spreads in the body.    - Cancer may spread from where it began to other parts of the body.    - Treatment for retinoblastoma depends on whether it is intraocular (within the eye) or extraocular (outside the eye).          - Intraocular retinoblastoma      - Extraocular retinoblastoma (metastatic)
                
                
                    After retinoblastoma has been diagnosed, tests are done to find out if cancer cells have spread within the eye or to other parts of the body.
                    The process used to find out if cancer has spread within the eye or to other parts of the body is called staging. The information gathered from the staging process determines whether retinoblastoma is only in the eye (intraocular) or has spread outside the eye (extraocular). It is important to know the stage in order to plan treatment. The results of the tests used to diagnose cancer are often also used to stage the disease. (See the General Information section.)   The following tests and procedures may be used in the staging process:         -   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 and is detected by a scanner that also takes a picture of the body. Areas of bone with cancer show up brighter in the picture because they take up more radioactive material than normal bone cells do.    -   Bone marrow aspiration and biopsy : The removal of bone marrow and a small piece of bone by inserting a hollow needle into the hipbone or breastbone. A pathologist views the bone marrow under a microscope to look for signs of cancer. A bone marrow aspiration and biopsy is done if the doctor thinks the cancer has spread outside of the eye.    -   Lumbar puncture : A procedure used to collect cerebrospinal fluid (CSF) from the spinal column. This is done by placing a needle between two bones in the spine and into the CSF around the spinal cord and removing a sample of the fluid. The sample of CSF is checked under a microscope for signs that the cancer has spread to the brain and spinal cord. This procedure is also called an LP or spinal tap.
                
                
                    The International Retinoblastoma Staging System (IRSS) may be used for staging retinoblastoma.
                    There are several staging systems for retinoblastoma. The IRSS stages are based on how much cancer remains after surgery to remove the tumor and whether the cancer has spread.      Stage 0     The tumor is in the eye only. The eye has not been removed and the tumor was treated without surgery.        Stage I    The tumor is in the eye only. The eye has been removed and no cancer cells remain.        Stage II     The tumor is in the eye only. The eye has been removed and there are cancer cells left that can be seen only with a microscope.        Stage III     Stage III is divided into stages IIIa and IIIb:            - In stage IIIa, cancer has spread from the eye to tissues around the eye socket.     - In stage IIIb, cancer has spread from the eye to lymph nodes near the ear or in the neck.               Stage IV     Stage IV is divided into stages IVa and IVb:            - In stage IVa, cancer has spread to the blood but not to the brain or spinal cord. One or more tumors may have spread to other parts of the body such as the bone or liver.     - In stage IVb, cancer has spread to the brain or spinal cord. It also may have spread to other parts of the body.
                
                
                    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 retinoblastoma spreads to the bone, the cancer cells in the bone are actually retinoblastoma cells. The disease is metastatic retinoblastoma, not bone cancer.
                
                
                    Treatment for retinoblastoma depends on whether it is intraocular (within the eye) or extraocular (outside the eye).
                    Intraocular retinoblastoma     In intraocular retinoblastoma, cancer is found in one or both eyes and may be in the retina only or may also be in other parts of the eye such as the choroid, ciliary body, or part of the optic nerve. Cancer has not spread to tissues around the outside of the eye or to other parts of the body.        Extraocular retinoblastoma (metastatic)    In extraocular retinoblastoma, cancer has spread beyond the eye. It may be found in tissues around the eye (orbital retinoblastoma) or it may have spread to the central nervous system (brain and spinal cord) or to other parts of the body such as the liver, bones, bone marrow, or lymph nodes.