Prognostic grouping: the next step in tumor classification.

At present, staging of malignant tumors is based on the anatomical extent of disease defined by the T(umor) N(odes) M(etastasis) classification. The main objective of further efforts in classifying tumors is to identify additional independent prognostic factors and to create mathematical models that may predict disease progression by prognostic grouping. This article summarizes problems, methods and the design of coordinated studies on prognostic grouping.