Wilms tumor is the most common form of kidney cancer in children. It is also called nephroblastoma. "Nephro" means kidney, and a "blastoma" is a tumor made of embryonic tissue that has not yet fully developed. Accounting for 7% of children’s cancer cases, approximately 500 children are diagnosed with Wilms tumor in the United States each year and about 75% of those diagnosed are under age 5.
The kidneys are a pair of organs located inside the body near the middle of the back. In adults, each kidney is about the size of a fist. Shaped like the beans that carry their name, the kidneys filter waste out of the bloodstream, creating urine which passes into the bladder.
The kidneys, like all organs of the body develop while a baby is still in the womb. Wilms tumor arises when a mistake occurs in a single embryonic or immature kidney cell. Rather than multiplying normally to become mature kidney cells, this change causes multiplication of new cells that grow out of control, eventually resulting in a mass called Wilms tumor.
Wilms tumor usually arises in one kidney (unilateral), but sometimes it can occur in both kidneys (bilateral). A Wilms tumor may grow without being detected until it becomes quite large. However, most are discovered before they have spread to other parts of the body.
The causes of all Wilms tumor are not known. However, some tumors appear to result from changes in one or more gene. In the majority of cases, the genetic changes occur only in the kidney cells and not in other cells of the body. However, in some cases, other parts of the body are also affected. Some patients with Wilms tumor are born with certain congenital anomalies, including absence of the iris of the eye (aniridia) or abnormalities of the urinary tract. Although it is rare, Wilms tumor sometimes runs in families, which further supports a genetic connection.
Other Kidney TumorsThe second most common kidney tumor is Clear Cell Sarcoma of the Kidney (CCSK). The symptoms, diagnostic tests and methods of treating CCSK are quite similar to those of Wilms tumor. Characteristics of clear cell sarcoma include:
- A much more widespread, slow growing pattern of metastasis (spreading to other areas of the body), which may include the lungs, brain, bones and soft tissue.
- CCSK is associated with a much higher rate of relapse than Wilms tumor.
- The treatment for CCSK is similar to the treatments for the more advanced stages of Wilms tumor.
- Renal cell carcinoma
- Malignant rhabdoid tumor
- Congenital mesoblastic nephroma
- Other kidney sarcomas