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