Nephroblastoma, light micrograph. Nephroblastoma, or Wilms tumour, is the fourth most common type of childhood cancer and the most common type of kidney cancer in children. The peak incidence is seen between 2 and 5 years of age. It is only rarely seen as a congenital neoplasm. They are usually solitary, large, and sharply demarcated tumours. About 7% are multicentric and 5% of cases are bilateral. In its classic microscopic appearance, Wilms tumour is triphasic and consists of variable proportions of blastema, stroma, and epithelial cells. One component may dominate over others in a given case, resulting in biphasic and monophasic variants. The blastemal component consists of highly cellular sheets of primitive small blue cells with scant cytoplasm. The epithelial component consists of abortive tubules and glomerular structures. Stroma is usually fibroblastic or loose myxoid in appearance. All three elements are clearly seen in this image.