Newborns and young children can develop a very rare tumor called Birch-Hirschfeld tumor, which is also known as Wilms tumor. This tumor is a type of nephroblastoma cancer, a malignant tumor that occurs in the kidneys. Kidneys exist to get rid of waste by filtering the blood, but kidney cancer is rare. Like other types of cancer, it grows and spreads to other organs until it becomes large. This means that patients with kidney cancer are at risk of the tissue spreading to surrounding structures in the body, including the liver, lungs and abdomen.