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.
Wilms' tumor was named after a German surgeon, Max Wilms, who published the first comprehensive review of the disease in 1899.
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.
Usually, Wilms' tumor 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.
What causes Wilms' tumor?
The causes of all Wilms' tumor are not known. However, some of these tumors appear to result from changes in one or more of several genes. 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.
Signs and symptoms of Wilms' tumor
The most common signs and symptoms of Wilms' tumor include:
A lump or mass in the abdomen of an otherwise well child
Abdominal pain
Blood in the urine
High blood pressure
Fever
Diarrhea
Weight loss
Urogenital infections
Anemia
Shortness of breath
A general feeling of being tired and unwell
Nausea and vomiting (these are rare)
Keep in mind that most children will not experience all of these symptoms.
Incidence of Wilms' tumor
Wilms' tumor is the most common form of kidney cancer in children. About 500 new cases of Wilms' tumor are diagnosed every year in the United States, and this number has not changed in many years. Wilms' tumor makes up about 7% of all cancers in children. The incidence of this tumor peaks at about three years of age, and becomes less common as children get older. It is very uncommon after the age of six years. Wilms tumor is slightly more common in girls, and among African Americans.
Wilms' tumor usually affects only one kidney. This is referred to as “unilateral” because it occurs on only one side of the body. About 5% of children with Wilms' tumor have this cancer in both kidneys ("bilateral").
Other tumors of the kidney
Approximately 15% of kidney tumors are childhood are not Wilms' tumor. Other kidney tumors include:
- Clear cell sarcoma of the kidney
- Renal cell carcinoma
- Malignant rhabdoid tumor
- Congenital mesoblastic nephroma
- Other kidney sarcomas
It is important to correctly identify these tumors becasue they are treated differently from Wilms tumor.
Factors that affect successful treatment
Generally, the prognosis for children with Wilms' tumor is very good. Currently, the great majority of children with Wilms' tumor are cured. Presently, nine out of ten children diagnosed with Wilms' tumor will be alive five years after diagnosis. This is due to improved surgical techniques, the use of combinations of drugs, and sometimes radiation treatments.
The overall five-year survival rate for children with Wilms tumor is approximately 90%. That means that 9 out of 10 children with Wilms tumor will live at least five years after their cancer is diagnosed. The five-year survival mark is the point at which a patient is considered "cured" since these tumors almost never recur later.
There are two major types of Wilms' tumors. These are identified based upon the types of cells that are found (histology) and impact the outcome. After the tumor or a portion of the tumor is removed, a pathologist will look at the cells that make up the tumor to identify the type of cells that make up the tumor.
Wilms' tumor of favorable histology
Favorable histology means there is no anaplasia (explained below), and that the chance of a cure is excellent. About 92% of Wilms' tumors have favorable histology.
Wilms' tumor of unfavorable histology
If a tumor has unfavorable histology, it means that the cells are more abnormal or bizarre appearing, and that the nuclei of the cancer cells (the part that contains the cells' DNA) are very large and distorted. This is called anaplasia. Anaplasia is predictive of a pooer chance of cure.
Shirley Perry, RN, Oncology Nurse Practitioner, Stollery Children's Hospital
Reviewed by the
CureSearch.org Medical Editorial Board
June 2008