This is the commonest kidney tumor seen in children. It is the 4th commonest type of cancer in childhood. It accounts for about 6% of all childhood tumors. The incidence is about 9/million children/year. Both boys and girls are equally affected and there is no racial predilection. Most children with Wilms' tumor present by the age of 5 years. In about 1% of cases there is a family history of Wilms' tumor. Wilms' tumor is also associated with some congenital abnormalities; these include:
- Congenital absence of iris of eyes (aniridia).
- Congenital malformation of the kidneys and the urinary system such as horseshoe kidneys, double ureter, and abnormalities of the penis.
- Congenital hemihypertrophy in which one half eof the body is much bigger than other half.
- Congenital abnormalities of the skeletal system such as clubfoot rib fusion, congenital hip dislocation.
- Pigmentation and vascular lesion in the skin such as hemangiomas, cafe-au-lait spots.
- Beckwith-Wiedemann Syndrome: children with this syndrome have enlarged kidneys, liver, adrenal glands and pancreas. They also have enlarged tongues, small head and mental retardation. Children with this syndrome have higher risks of developing Wilms' tumor, hepatoblastoma (tumor of the liver) and gonadoblastoma (tumor of the reproductive organs).
Most children present with abdominal mass. The kidneys are involved in control of blood pressure and it is not uncommon for some children with Wilms' tumor present with hypertension (high blood pressure). Other symptoms include
- Blood in the urine ( known as hematuria)
- Weight loss
- Urinary tract infection
- Nausea and vomiting
- Abdominal pain
- Inguinal hernia
- Increased number of red blood cells in the blood (Polycythemia)
Investigation and diagnosis
A good history and physical examination is essential. This should also be done to identify congenital abnormalities that may have been missed previously.
Laboratory investigation include:
- Blood count and chemistry
- Examination of the urine
- Abdominal ultrasound
- Abdominal CT scan: This will help determine approximate size of tumor. One can also assess the other kidney to see if it is present and if it is functioning.
- Chest CT scan because this tumor tend s to spread into the lungs.
- EKG and echocardiogram to asses the function of the heart.
- Radiation therapy
Clinical staging depends on findings at surgery and presence or absence of spread to surrounding tissue and distant organs. There are 5 clinical groupings or stages. These are stage I, II, III, IV and V. The higher the stage the more advance and widespread the disease (tumor). Stage I denotes a tumor that is localized to only one kidney while stage IV denotes that the tumor has gone beyond the kidney and now involves organ such as lung, liver, bone and brain. Stage V indicates that the tumor involves both kidneys.
Surgery is recommended is to remove as much of the tumor as possible. Sometimes this entails removing the entire kidney. If the second kidney is present, functioning well and has no tumor this is possible if not as much of the tumor is removed from the affected kidney. It is hoped that whatever is left behind will be enough to perform the normal excretory function of the kidney. If both kidneys are affected, a biopsy of both kidneys is first obtained and based on this chemotherapy is determined. Excision of tumor is performed at initial operation only if the entire tumor can be removed with preservation of sufficient kidney tissue on one or both sides for normal kidney function. It is not unusual for patients to develop problems with kidney excretory function especially when they receive chemotherapy agents, which sometimes have toxic side effects on the kidney but are required for adequate treatment of the tumor. The dosing of these drugs are adjusted to accommodate changes in kidney function.
This is usually started shortly after surgery. Radiation therapy is required for patients with stage II, II and IV disease. The reason for giving radiation therapy is to kill any tumor cells that may have escaped into the abdomen at the time of surgery. The radiation is target to the region where the tumor was localized along with the surrounding area. The second kidney is shielded from the radiation field. If the tumor has spread to the lungs the lungs also get radiated.
Generally chemotherapy is started about a week after surgery. The duration of chemotherapy depends on the clinical staging and the histology (degree of maturation and differentiation) of tumor cells. The histology is said to be favorable or unfavorable. Patients with stage 1 tumors are generally treated for about 6 months. Patients with stage II, III and IV tumors are treated for 15 months. Chemotherapy consists of repeated cycles of 2 or 3 drugs depending on the clinical stage and histology.
Prognosis depends on the clinical stage of the disease and the histology of the tumor. Prognosis is better in patients with more localized tumors. Overall patients with stage I tumors and favorable histology have 98% survival after 4 years. If histology is unfavorable survival rate is about 89% in patients with stage 1 disease. Patients with stage IV tumors have about 80% survival after 4 years provided the histology is favorable. If it is unfavorable survival rate drops to about 50%.