After cancer has been diagnosed, doctors ask the following three questions to determine how far the disease has progressed: How large is the tumor, and how deeply has it invaded surrounding tissues? Have cancer cells spread to regional lymph nodes? Has the cancer spread (metastasized) to other regions of the body? Based on the answers to these questions, the cancer is assigned a "stage." A patient's chances for survival are better when cancer is detected at a lower stage. Staging describes the severity of a person’s cancer based on the extent of the original (primary) tumor and whether or not cancer has spread in the body. Staging is important for several reasons: Staging helps the doctor plan the appropriate treatment. The stage can be used to estimate the person’s prognosis. Knowing the stage is important in identifying clinical trials that may be suitable for a particular patient. Staging helps health care providers and researchers exchange information about patients; it also gives them a common terminology for evaluating the results of clinical trials and comparing the results of different trials. Staging is based on knowledge of the way cancer progresses. Cancer cells grow and divide without control or order, and they do not die when they should. As a result, they often form a mass of tissue called a tumor. As the tumor grows, it can invade nearby tissues and organs. Cancer cells can also break away from the tumor and enter the bloodstream or the lymphatic system. By moving through the bloodstream or lymphatic system, cancer cells can spread from the primary site to lymph nodes or to other organs, where they may form new tumors. The spread of cancer is called metastasis. Source :cancer.gov
