Background: In young children and infants, Wilms' tumor is the most common cancer of the kidney. Wilms' tumor exhibits heterogeneous histopathologic features, consisting of rapidly proliferating blastemal and epithelial cells and a stromal component that has heterologous elements (e.g., cartilage, bone, and striated muscle). It is unclear whether the stromal and heterologous components of sporadic Wilms' tumor are neoplastic or should be considered non-neoplastic.
Purpose: Our purpose was twofold: 1) to selectively analyze the different histologic tissue components of sporadic Wilms' tumors, including blastemal, epithelial, stromal, and heterologous elements, for loss of heterozygosity (LOH) of the WT1 gene and for expression of the WT1 gene and 2) to determine the role of WT1 gene expression in the development of these tissues.
Methods: By use of tissue microdissection techniques, various histologic elements (blastema, stroma, epithelium, and striated muscle) of sporadic Wilms' tumor were obtained from specimens taken from 18 patients. DNA was extracted from the dissected tissue fragments, and DNA solutions were amplified by use of the polymerase chain reaction and the polymorphic genomic markers D11S1392 and D11S904 to detect LOH at the WT1 gene locus (11p13). Three selected specimens with heterologous elements and LOH at 11p13 were analyzed for expression of the WT1 gene by means of the in situ reverse transcription-polymerase chain reaction.
Results: Nine (50%) of the 18 specimens showed LOH at the WT1 locus. Although identical WT1 gene deletion was consistently observed in all of the various histologic components of these nine specimens, WT1 gene expression was high in the blastemal and epithelial elements and low in the stromal and heterologous elements.
Conclusions and implications: Identical allelic deletion at 11p13 in all components of the sporadic Wilms' tumors examined suggests that the stromal tissue components are neoplastic rather than non-neoplastic. In conjunction with variable WT1 gene expression in the different histologic components, the results raise the possibility that undifferentiated blastemal cells are the precursors of the stromal and heterologous elements. Morphologically benign stromal and heterologous elements may therefore be derived from neoplastic cells. The developmental state of the various tissue components of Wilms' tumor may be attributed to an altered residual WT1 gene that is required for the maturation of blastemal and epithelial cells but that is not required for the maturation of stromal and heterologous elements.