Staging is the process of classifying a tumor, especially a malignant tumor, with respect to its degree of differentiation as well as its local and distant extent, in order to estimate the prognosis for the patient. Evaluation of the histological and imaging studies of a tumor allows the physician to formulate a rational strategy for treatment with operative intervention, medical therapy, or radiation therapy. Staging a tumor is a valuable process in the management of individual patients. In contrast, staging systems are based on clinical, radiographic, and histological features that are believed to be of prognostic importance and may be useful when outcomes are compared between groups of patients. Staging systems may be used to compile data on patient survival and recurrence for tumors that have similar features and to evaluate the effectiveness of therapy for such tumors.