With the innovation in cancer treatment and the trend of modem oncology toward a great number of differentiated treatment options, prognostic factor assessment has become more important. Thus, in 1993, the International Union Against Cancer (UICC) began a program of researching prognostic factors in malignant tumors. The anatomic extent of disease and histological type are generally the most important indicators of prognosis cancer patients and provide the main criteria for selecting therapy, they may not be sufficient to provide a powerful prognostic assessment. It has been recognized that other factors have a profound impact on prognosis of cancer patients. The purpose of this paper is to provide the framework for the consideration of prognostic factor, the application of prognostic factor to clinical practice, and deal with methodology of studying.