Wilms' tumor

Definition

Wilms' tumor is a cancerous tumor of the kidney that usually occurs in young children.

Description

When an unborn baby is developing, the kidneys are formed from primitive cells. Over time, these primitive cells become more specialized. The cells mature and organize into the normal kidney structures. Sometimes, clumps of these cells remain in their original, primitive form. If these cells begin to multiply after birth, they may ultimately form a large mass of abnormal cells. This is known as a Wilms' tumor.

Wilms' tumor is a type of malignant tumor. This means that it is made up of cells that are significantly immature and abnormal. These cells are also capable of invading nearby structures within the kidney and traveling out of the kidney into other structures. Malignant cells can even travel through the body to invade other organ systems, most commonly the lungs and brain. These features of Wilms' tumor make it a type of cancer that, without treatment, would eventually cause death. However, advances in medicine during the last 20 years have made Wilms' tumor a very treatable form of cancer.

Wilms' tumor occurs almost exclusively in young children. The average patient is about three years old. Females are only slightly more likely than males to develop Wilms' tumors. Wilms' tumors are found more commonly in patients with other types of birth defects. These defects include:

• Absence of the colored part (the iris) of the eye (aniridia)
• Enlargement of one arm, one leg, or half of the face (hemihypertrophy)
• Certain birth defects of the urinary system or genitals
• Certain genetic syndromes (WAGR syndrome, Denys-Drash syndrome, and Beckwith-Wiedemann syndrome).

Causes & symptoms

The cause of Wilms' tumor is not totally understood. Because 15% of all patients with this type of tumor have other genetic defects, it seems clear that at least some cases of Wilms' tumor may be due to a genetic defect. It appears that the tendency to develop a Wilms' tumor can run in families. In fact, about 1-2% of all children with a Wilms' tumor have family members who have also had a Wilms' tumor.

Some patients with Wilms' tumor experience abdominal pain, nausea, vomiting, high blood pressure, or blood in the urine. However, the parents of many children with this type of tumor are the first to notice a firm, rounded mass in their child's abdomen. This discovery is often made while bathing or dressing the child, and frequently occurs before any other symptoms appear. Rarely, a Wilms' tumor is diagnosed after there has been bleeding into the tumor, resulting in sudden swelling of the abdomen and a low red blood cell count (anemia).

Diagnosis

Initial diagnosis of Wilms' tumor is made by looking at the tumor using various imaging techniques. Ultrasound and computed tomography scans (CT scans) are helpful in diagnosing Wilms' tumor. Intravenous pyelography, where a dye injected into a vein helps show the structures of the kidney, can also be used in diagnosing this type of tumor. Final diagnosis, however, depends on obtaining a tissue sample from the mass (biopsy), and examining it under a microscope in order to verify that it has the characteristics of a Wilms' tumor. This biopsy is usually done during surgery to remove or decrease the size of the tumor. Other studies (chest x rays, CT scan of the lungs, bone marrow biopsy) may also be done in order to see if the tumor has spread to other locations.

Treatment

Treatment for Wilms' tumor almost always begins with surgery to remove or decrease the size of the kidney tumor. Except in patients who have tumors in both kidneys, this surgery usually will require complete removal of the affected kidney. During surgery, the surrounding lymph nodes, the area around the kidneys, and the entire abdomen will also be examined. Additional biopsies of these areas may be done to see if the cancer has spread. The next steps of treatment depend on whether/where the cancer has spread. Samples of the tumor are also examined under a microscope to determine particular characteristics of the cells making up the tumor.

Information about the tumor cell type and the spread of the tumor is used to decide the best kind of treatment for a particular patient. Treatment is usually a combination of surgery, medications used to kill cancer cells (chemotherapy), and x rays or other high energy rays used to kill cancer cells (radiation therapy).

Prognosis

The prognosis for patients with Wilms' tumor is quite good, compared to the prognosis for most types of cancer. The patients who have the best prognosis are usually those who have a small-sized tumor, a "favorable" cell type, are young (especially under two years old), and have an early stage of cancer that has not spread. The average two-year survival rate for children with Wilms' tumor is 92%.

Prevention

There are no known ways to prevent a Wilms' tumor, although it is important that children with birth defects associated with Wilms' tumor be carefully monitored.

Key Terms

Biopsy

A procedure where a small sample of tissue is removed, prepared, and then examined with a microscope to determine the characteristics of the tissue's cells.

Cancer

A process where abnormal cells within the body begin to grow out of control, acquire the ability to invade nearby structures, and travel through the bloodstream in order to invade distant structures.

Malignant

Refers to cancer or cancer cells.

Further Reading

For Your Information

Books

• Shearer, Patricia D., and Judith A. Wilimas. "Neoplasms of the Kidney." In Nelson Textbook of Pediatrics, edited by Richard Behrman. Philadelphia: W. B. Saunders Co., 1996.
• Steuber, C. Philip, and Donald J. Fernbach. "Neoplasms of the Kidney or Suprarenal Area." In Principles and Practice of Pediatrics, edited by Frank A. Oski, et al. Philadelphia: J. B. Lippincott Company, 1994.

  Periodicals

• Haase, G. M. "Current Surgical Management of Wilms' Tumor." Current Opinions in Pediatrics, 8 (1996): 268+.

  Organizations

• American Cancer Society. 1515 Clifton Rd. NE, Atlanta, GA 30329. (800) 227-2345. http://www.cancer.org.
• March of Dimes Birth Defects Foundation, National Office. 1275 Mamaroneck Ave., White Plains, NY 10605. http://www.modimes.org.

Gale Encyclopedia of Medicine. Gale Research, 1999.