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A risk factor is anything that raises a person's chance of having a disease such as cancer. Different cancers have different risk factors.

Lifestyle-related risk factors such as body weight, physical activity, diet, and tobacco use play a major role in many adult cancers. But these factors usually take many years to influence cancer risk, and they are not thought to have much of an effect on the risk of childhood cancers, including Wilms tumors.

So far, research hasn't found any strong links between Wilms tumor and environmental factors, either during a mother’s pregnancy or after a child’s birth.

Most Wilms tumors have no clear cause, but there are some factors that affect risk.

Age

Wilms tumors are most common in young children, with the average age being about 3 to 4 years. They are less common in older children, and rare in adults.

Race/ethnicity

In the United States, the risk of Wilms tumor is slightly higher in African American children than in White children and is lowest among Asian American children. The reason for this is not known.

Sex

Wilms tumors are slightly more common in girls than in boys.

Family history of Wilms tumor

About 1% to 2% of children with Wilms tumors have one or more relatives with the same cancer. Scientists think that these children inherit chromosomes with an abnormal or missing gene from a parent that increases their risk of developing Wilms tumor.

Children with a family history of Wilms tumors are slightly more likely to have tumors in both kidneys. Still, in most children only one kidney is affected.

Certain genetic syndromes/birth defects

There is a strong link between Wilms tumors and certain kinds of birth defects. About 1 child in 10 with Wilms tumor also has birth defects. Most birth defects linked to Wilms tumors occur in syndromes. A syndrome is a group of symptoms, signs, malformations, or other abnormalities that occur together in the same person. Syndromes linked to Wilms tumor include:

WAGR syndrome

WAGR stands for the first letters of the physical and mental problems linked with this syndrome (although not all children have all of them):

• Wilms tumor
• Aniridia (complete or partial lack of the iris [colored area] of the eyes)
• Genitourinary tract abnormalities (defects of the kidneys, urinary tract, penis, scrotum, clitoris, testicles, or ovaries)
• Mental Retardation

Children with this syndrome have about a 30% to 50% chance of having a Wilms tumor. The cells in children with WAGR syndrome are missing part of chromosome 11, where the WT1 gene is normally found (see What Causes Wilms Tumors?). Children with WAGR tend to get Wilms tumors at an earlier age and often have tumors in both kidneys.

Denys-Drash syndrome and Frasier syndrome

These rare syndromes have also been linked to changes (mutations) in the WT1 gene.

In Denys-Drash syndrome, the kidneys become diseased and stop working when the child is very young. Wilms tumors usually develop in the diseased kidneys. The reproductive organs don’t develop normally, and boys may be mistaken for girls. Because the risk of Wilms tumors is very high, doctors often advise removing the kidneys soon after this syndrome is diagnosed.

In Frasier syndrome the kidneys are also diseased, but they usually keep working into adolescence. As with Denys-Drash syndrome, the reproductive organs don’t develop normally. Children with Frasier syndrome are also at increased risk for Wilms tumors, although they are at even higher risk for cancers in the reproductive organs.

Beckwith-Wiedemann syndrome

Children with this syndrome tend to be big for their age. They also have larger than normal internal organs and often have an enlarged tongue. They may have an oversized arm and/or leg on one side of the body (called hemihypertrophy), as well as other medical problems. They have about a 5% risk of having Wilms tumors (or, less often, other cancers that develop during childhood). This syndrome is caused by a defect in chromosome 11 that affects the WT2 gene.

Other syndromes

Less often, Wilms tumor has been linked to other syndromes, including:

• Perlman syndrome
• Sotos syndrome
• Simpson-Golabi-Behmel syndrome
• Bloom syndrome
• Li-Fraumeni syndrome
• Trisomy 18

Certain birth defects

Wilms tumor is also more common in children with certain birth defects (without known syndromes):

• 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)