Wilms tumor (also called Wilms’ tumor or nephroblastoma) is a type of childhood cancer that starts in the kidneys. It is the most common type of kidney cancer in children. About 9 of 10 kidney cancers in children are Wilms tumors.
Cancer starts when cells in the body begin to grow out of control. Cells in nearly any part of the body can become cancer, and can spread to other areas of the body
Wilms tumors are grouped into 2 major types based on how they look under a microscope (their histology):
Favorable histology: The cancer cells in these tumors don’t look quite normal, but there is no anaplasia (see next paragraph). About 9 of 10 Wilms tumors have a favorable histology. The chance of curing children with these tumors is very good.
Anaplastic histology: In these tumors, the look of the cancer cells varies widely, and the cells’ nuclei (the central parts that contain the DNA) tend to be very large and distorted. This is called anaplasia. In general, tumors in which the anaplasia is spread throughout the tumor (known as diffuse anaplasia) are harder to treat than tumors in which the anaplasia is limited just to certain parts of the tumor (known as focal anaplasia).