What are the stages of Oropharyngeal Cancer ? 

Key Points
                    - After oropharyngeal cancer has been diagnosed, tests are done to find out if cancer cells have spread within the oropharynx 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 oropharyngeal cancer:         - Stage 0 (Carcinoma in Situ)     - Stage I     - Stage II     - Stage III     - Stage IV
                
                
                    After oropharyngeal cancer has been diagnosed, tests are done to find out if cancer cells have spread within the oropharynx or to other parts of the body.
                    The process used to find out if cancer has spread within the oropharynx 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 results of some of the tests used to diagnose oropharyngeal cancer are often used to stage the disease.
                
                
                    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 oropharyngeal cancer spreads to the lung, the cancer cells in the lung are actually oropharyngeal cancer cells. The disease is metastatic oropharyngeal cancer, not lung cancer.
                
                
                    The following stages are used for oropharyngeal cancer:
                    Stage 0 (Carcinoma in Situ)    In stage 0, abnormal cells are found in the lining of the oropharynx. 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 is 2 centimeters or smaller and is found in the oropharynx only.       Stage II    In stage II, the cancer is larger than 2 centimeters but not larger than 4 centimeters and is found in the oropharynx only.        Stage III    In stage III, the cancer is either:            - 4 centimeters or smaller; cancer has spread to one lymph node on the same side of the neck as the tumor and the lymph node is 3 centimeters or smaller; or     - larger than 4 centimeters or has spread to the epiglottis (the flap that covers the trachea during swallowing). Cancer may have spread to one lymph node on the same side of the neck as the tumor and the lymph node is 3 centimeters or smaller.              Stage IV     Stage IV is divided into stage IVA, IVB, and IVC:            - In stage IVA, cancer:                  - has spread to the larynx, front part of the roof of the mouth, lower jaw, or muscles that move the tongue or are used for chewing. Cancer may have spread to one lymph node on the same side of the neck as the tumor and the lymph node is 3 centimeters or smaller; or       - has spread to one lymph node on the same side of the neck as the tumor (the lymph node is larger than 3 centimeters but not larger than 6 centimeters) or to more than one lymph node anywhere in the neck (the lymph nodes are 6 centimeters or smaller), and one of the following is true:                           - tumor in the oropharynx is any size and may have spread to the epiglottis (the flap that covers the trachea during swallowing); or          -  tumor has spread to the larynx, front part of the roof of the mouth, lower jaw, or muscles that move the tongue or are used for chewing.                                 - In stage IVB, the tumor:                  - surrounds the carotid artery or has spread to the muscle that opens the jaw, the bone attached to the muscles that move the jaw, nasopharynx, or base of the skull. Cancer may have spread to one or more lymph nodes which can be any size; or       - may be any size and has spread to one or more lymph nodes that are larger than 6 centimeters.                - In stage IVC, the tumor may be any size and has spread beyond the oropharynx to other parts of the body, such as the lung, bone, or liver.