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Wilms' Tumor Facts

Wilms' tumor is a rare type of kidney cancer that affects children. It also is called nephroblastoma. The disease is named after the German doctor who discovered it in 1899, Max Wilms.

According to the American Cancer Society, about 500 children, most between ages 2 and 5, are diagnosed with Wilms' tumor each year in this country. While it is rare, it is the most common type of kidney cancer in children.

If Wilms' tumor is found and treated in the early stages, the chances for successful treatment are as high as 95%.

Problems that cause Wilms' tumor may begin before birth. As kidney cells mature in the fetus, they become specialized and form different parts of the kidney. Some of the cells continue developing after birth and mature over the next three or four years.

However, in children with Wilms' tumor, the cells remain immature. They begin to grow and reproduce too quickly, forming a tumor.

Wilms' tumor generally forms one tumor in one kidney. In rare cases, there may be more than one tumor in one kidney or tumors in both kidneys.

Because they grow rapidly and often don't have early symptoms, Wilms' tumors may be large when they are found. Sometimes they spread to other parts of the body, particularly the lungs.

Types of Wilms' Tumors

Wilms' tumors can be classified into two categories depending on how they appear when they are examined with a microscope.

Favorable histology: Almost all Wilms' tumors are this type. The cells are slightly abnormal. Chances for successful treatment are good.

Unfavorable histology (anaplastic Wilms' tumor): The cell area that holds the DNA is large and distorted, or anaplastic. Anaplastic tumors are more difficult to treat successfully.

Wilms' Tumor Risk Factors

Anything that increases your child's chance of getting Wilms' tumor is a risk factor. Although we don't know exactly what causes Wilms' tumors, some things may make your child more likely to develop the disease.

Risk factors include:

  • Age: Most children who develop Wilms' tumors are between 3 and 5 years old
  • Race: Wilms' tumor is more common in African American children. It is least prevalent in Asian American children
  • Gender: It is more common in females
  • Birth defect syndromes, including:
    • WAGR
    • Beckwith-Wiedemann
    • Denys-Drash
  • Other birth defects, including:
    • Aniridia (complete or partial lack of the iris [colored area] of the eyes)
    • Hemihypertrophy (an oversized arm and/or leg on one side of the body)
    • Cryptorchidism (failure of the testicles to descend into the scrotum) in boys
    • Hypospadias (defect in boys where the urinary opening is on the underside of the penis)
  • Other genetic conditions, including:
    • Perlman syndrome
    • Sotos syndrome
    • Simpson-Golabi-Behmel syndrome
    • Bloom syndrome
    • Li-Fraumeni syndrome
    • Frasier syndrome
    • Trisomy 18

Not everyone with risk factors gets Wilms' tumor. However, if your child has risk factors, you should discuss them with your doctor.

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