National Wilms Tumor Study: an update for pathologists.

The National Wilms Tumor Study (NWTS)-5, begun in August 1995, incorporates some important new definitions and concepts that have critical importance in determining therapy and prognosis. The criteria for stage 1 were refined to accommodate an important subset of stage 1 Wilms tumors that are being managed by nephrectomy alone, without the use of adjuvant therapy. The distinction between stages 1 and 2 in the renal sinus is no longer defined by the hilar plane but by the presence or absence of venous or lymphatic invasion. Specific problems encountered in the interpretation of the renal sinus are discussed here. The topographical definition of focal anaplasia has proven to be of prognostic value and is incorporated into the NWTS-5 study design.