Precursor lesions of Wilms tumor: clinical and biological implications.

Nephrogenic rests (NR) are persistent embryonal remnants in the kidney that are apparent precursors of Wilms tumor (WT). Nephroblastomatosis (Nbl) denotes multiple or diffuse NR. Two major categories of NR have been recognized to date, perilobar (PLNR) and intralobar (ILNR). A dynamic classification of NR according to their recognized developmental fates is presented. Dormancy, maturation, involution, hyperplastic overgrowth, and neoplastic induction are the common fates of NR. Hyperplastic NR are far more common than formerly recognized, and are frequently confused with WT, especially in cases of multicentric and bilateral tumors. Biopsy is of limited value in distinguishing hyperplastic NR from WT, and the use of surgery in cases of Nbl requires careful consideration, as its role can in many cases be reduced or supplanted due to the effectiveness of modern imaging techniques and chemotherapy. An understanding of the natural history of NR and Nbl is essential for rational patient care decisions, and is important for understanding the molecular biology of WT.