Wilms' tumor: a paradigm, a parallel, and a puzzle.

Wilms' tumor, a childhood tumor of the kidney, parallels retinoblastoma in several ways. Both malignancies occur in the very young, involve paired organs, arise from embryonal cells, can develop unilaterally or bilaterally, and can occur in hereditary and non-hereditary forms. However, Wilms' tumor rarely occurs in family clusters and may involve the loss of function of multiple genes.