Expression of MIB and BCL-2 in patients with nephrogenic rests with and without associated Wilms' tumors

Nephrogenic rests (NR) are foci of persistent embryonal renal tissue. Because it has been suggested that NRs are precursor lesions to Wilms' tumor (WT), they are of considerable clinical interest. NRs vary from microscopic foci to macroscopic renal tumors, but only a few progress to WT. In this study, patients with NRs detected during the treatment of bilateral WT were compared to a group of patients with NRs incidentally discovered in various clinical settings. Because mechanisms leading to NR growth and WT formation are poorly understood, bcl-2 and MIB expression were studied by immunohistochemistry in both groups. Bcl-2 is an oncoprotein with inhibitory effects on apoptosis and MIB is a well-established marker of cell proliferation. Both mechanisms may be of interest for the growth, regression and transformation of NRs. Intense positive staining for bcl-2 was found in microscopic NRs. Blastemal cells and cells with epithelial differentiation were bcl-2-positive. The same pattern of bcl-2 expression was found in NRs with and without associated WT. High proliferative activity with intense MIB expression was found in blastemal areas of WT. Bcl-2 expression in NR is reported for the first time. Inhibition of apoptosis as a mechanism of NR formation is suggested. This is of special interest, because bcl-2 is under transcriptional control of the WT-1 gene.