This is a Wilms tumor that is composed microscopically of nests and sheets of dark blue cells at the left with compressed normal renal parenchyma at the right. The WT1 gene at chromosomal band 11p13 encodes a transcription factor needed for renal development. There can be familial germline mutations (WAGR syndrome; Denys-Drash syndrome), but most Wilms tumors arise from acquired mutations.

The child's parent asks, "Why did this happen?

AnswerI am sorry. This could happen to any child. It is not your fault. We will do our best to treat this illness. Your loving care will help.