Signs and symptoms of Wilms' tumor vary widely, and some children don't show any obvious signs. But most children with Wilms' tumor experience one or more of these signs and symptoms:

• An abdominal mass you can feel
• Abdominal swelling
• Abdominal pain

Other signs and symptoms may include:

• Fever
• Blood in the urine
• Nausea or vomiting or both
• Constipation
• Loss of appetite
• Shortness of breath
• High blood pressure

It's not clear what causes Wilms' tumor, but in rare cases, heredity may play a role.

Cancer begins when cells develop errors in their DNA. The errors allow the cells to grow and divide uncontrollably and to go on living when other cells would die. The accumulating cells form a tumor. In Wilms' tumor, this process occurs in the kidney cells.

In rare cases, the errors in DNA that lead to Wilms' tumor are passed from a parent to the child. In most cases, there is no known connection between parents and children that may lead to cancer.

Factors that may increase the risk of Wilms' tumor include:

• African-American race. In the United States, African-American children have a slightly higher risk of developing Wilms' tumor than children of other races. Asian-American children appear to have a lower risk than children of other races.
• Family history of Wilms' tumor. If someone in your child's family has had Wilms' tumor, then your child has an increased risk of developing the disease.

Wilms' tumor occurs more frequently in children with certain abnormalities or syndromes present at birth, including:

• Aniridia. In aniridia (an-ih-RID-e-uh), the iris — the colored portion of the eye — forms only partially or not at all.
• Hemihypertrophy. Hemihypertrophy (hem-e-hi-PUR-truh-fee) means one side of the body or a part of the body is noticeably larger than the other side.

Wilms' tumor can occur as part of rare syndromes, including:

• WAGR syndrome. This syndrome includes Wilms' tumor, aniridia, genital and urinary system abnormalities, and intellectual disabilities.
• Denys-Drash syndrome. This syndrome includes Wilms' tumor, kidney disease and male pseudohermaphroditism (soo-do-her-MAF-roe-dit-iz-um), in which a boy is born with testicles but may exhibit female characteristics.
• Beckwith-Wiedemann syndrome. Children with this syndrome tend to be significantly larger than average (macrosomia). Other signs may include abdominal organs that jut out into the base of the umbilical cord, a large tongue (macroglossia), enlarged internal organs and ear abnormalities. There is also an increased risk of tumors, including a type of liver cancer called hepatoblastoma.