Eight cases of
congenital mesoblastic nephroma (CMN) were examined. Three CMNs were of the classical (typical) variant, two were cellular (atypical), and three showed a mixed pattern. A panel of nephron segment-specific tubular epithelial markers (the
lectins Tetragonolobus purpureas, Phaseolus vulgaris erythroagglutinin, and Arachis hypogaea and
antibodies to
epithelial membrane antigen,
cytokeratin, and
Tamm-Horsfall protein) were used to differentiate epithelial structures within the
tumor.
Antibodies against
vimentin,
desmin, and muscle-specific actin were used as mesenchymal markers. A
monoclonal antibody to the long (embryonic) form of
polysialic acid (PSA) on the
neural cell adhesion molecule was used as a putative renal oncodevelopmental marker. An antibody to
proliferating cell nuclear antigen also was applied, which revealed increased proliferative rate in cellular CMNs. In addition to clearly entrapped native renal tubules, CMNs contain tubular structures with immature, dysplastic epithelium and occasional epithelial cell clusters embedded deep within the
tumor. These immature tubules and clusters express distal nephron, including collecting duct markers and, occasionally,
vimentin and PSA. We propose that these primitive tubules and epithelial structures may originate from the ureteric bud. An epithelial differentiation of the
tumor cells also is possible. In one pure cellular CMN and two mixed CMNs the cellular component showed diffuse staining for PSA. The PSA (
neural cell adhesion molecule) expression of the cellular component suggests that CMN may originate from the uninduced nephrogenic mesenchyme.