Wilms tumor in monozygous twins: clinical, pathological, cytogenetic and molecular case report.

The concomitant occurrence of Wilms tumor (WT) was observed in two monozygotic twin sisters without evidence of congenital malformations. Twin 1 was diagnosed with a stage I WT at 11 months of age, whereas twin 2 developed a bilateral (stage V) WT at 13 months of age. In both cases pathologic examination showed a nonanaplastic stromal type WT, with marked rhabdomyomatous elements. Cytogenetic analyses performed on blood samples and on tumor specimens revealed no karyotypic abnormality. No alteration of the WTI and POU6F2 genes was identified in constitutional and tumor DNA of both sisters, and no anomaly in WT1 expression was evidenced in the normal kidney of one of them. However, loss of heterozygosity on chromosome 11p, involving the alleles of maternal origin, was detected both in the single tumor of twin 1 and in the two distinct tumors of twin 2, thus suggesting a common etiology of the diseases. To the authors' knowledge, this is the first report describing at both the clinical and genetic level a couple of monozygotic twins concordant for WT development.