FOR THE PAST 50 YEARS, patients with cancer have been staged according to the morphologic extent of the tumor using the TNM staging system. Originally described by Denoix and Schwartz1 in 1948, the TNM staging system of cancer classification was incorporated in 1953 by the International Union Against Cancer (Union International Contre le Cancer [UICC]) and by the International Congress of Radiology into a formal classification system for cancer.2 The TNM staging system became adopted in the United States in 1959 when the American College of Surgeons, the American College of Radiology, the College of American Pathologists, the American College of Physicians, the American Cancer Society, and the National Cancer Institute sponsored the formation of the American Joint Committee for Cancer (AJCC) Staging and End Results Reporting.3