Wilms tumour or nephroblastoma as it is more commonly known is the most common renal malignancy in children. The annual incidence of renal tumours is about seven cases per million in children younger than 15 years of age. Two thirds of the cases of Wilms tumours are diagnosed before the age of five. Wilms tumour accounts for approximately 6% of all childhood malignancies.
Nephroblastoma can originate or affect one or both of the kidneys at the same time. Wilms tumour is associated with several congenital abnormalities (genetic or inherited abnormalities). Children that developed bilateral or are affected in both kidneys are more likely to have an inherited or a genetic abnormality. Although this is not always the case.
It is generally accepted that Wilms tumours are caused by abnormal renal or kidney development. This abnormal development results in growth of atypical, primitive tissue in the kidney. This abnormal growth does not function like normal kidney tissue and grows rapidly, compressing the normal tissue. Wilms tumour can spread to the surrounding tissue or enter the blood stream and form metastatic tumours in the lungs and even the brain.
Symptoms and clinical signs:
Most children present with a hard abdominal mass or swelling. This can also be an incidental finding when a child is examined for an unrelated condition. More often than not there is no pain associated. Some children may however present with mild abdominal pain or haematuria (blood in urine), fever or high blood pressure. Tumours that have started to bleed or rupture can cause acute abdominal pain and will require urgent medical attention.
Once the diagnosis is suspected a series of tests will be conducted to confirm the diagnosis. These tests will include an ultrasound examination of the abdomen, this is where ultrasound is used to visualise organ structures in the abdomen. This investigation is not diagnostic but will certainly tell the doctor that there is a mass originating from the kidney. The next important test is an abdominal CT scan. This will show a typical mass originating from the kidney and in most cases this can be diagnostic. Doctors may not request to a biopsy if there is any doubt about the diagnosis. A biopsy is where a small needle is placed through the skin and into the tumour and a small piece of the mass is removed. This is then examined under microscope and a final diagnosis of nephroblastoma is confirmed. A chest x-ray is a valuable tool to exclude any spread of the tumour to the lungs, blood test are performed to make sure it is safe to proceed with chemotherapy.
A common question that is often asked by patients as soon as they are diagnosed is what the stage. Staging a nephroblastoma is complicated. The size, spread and nature of the tissue is assessed to determine the stage.
Stage I: is where the tumour is confined to the kidney and is engulfed in a capsule.
Stage II: is where the tumour extends beyond the capsule of the kidney but is completely removed by surgery
Stage III: is when after surgery some tissue remains behind is confined to the abdomen with no spread to the lungs or to the lymph nodes.
Stage IV: is when after surgery there is evidence that the tumour has spread via the blood system. The tumour may be positioned in the lung, liver, bone or even the brain.
Stage V: is when both kidneys are involved, each kidney is staged separately for example you can have a stage V Wilms tumour with stage II, left and the stage I, right kidney tumour.
Once the kidney has been removed surgically it is examined and the nature of the tumour cells are assessed based on the tumour cells. The tumour is classified as a high-risk, standard risk or low risk tumour.
Wilms tumour is treated with a combination of chemotherapy, surgery and on occasion radiotherapy. Neoadjuvant therapy (this is where chemotherapy is given prior to surgery) is offered to patients with Wilms tumour. This is chemotherapy that is given 4 to 6 weeks prior to surgery with the aim of reducing the size of the tumour and limiting the possibility of spread, this also done to test the sensitivity of the tumour to chemotherapy.
Following this children undergo surgery whereby tumour and often the effected kidney is removed. The post-operative staging determines what adjuvant chemotherapy will be offered. Depending on the stage and risk this can range from 4 to 34 weeks.
At the end of treatment children are followed up for an extended period of time to make sure that the tumour does not return. Care is also taken to assess if there are any long-term side effects from the treatment. At these visits children will receive a thorough clinical exam, have a chest x-ray and an abdominal sonar, blood pressure will be monitored and kidney function tests will be performed. Certain children that have received prolonged courses of chemotherapy will also have heart sonar every five years following the completion of treatment.
Wilms tumour is one of the most common solid tumours occurring in children between ages of four and six years of age. It can affect one or both kidneys. Provided it is detected early and managed correctly it can be cured. There are some syndromes that will need closer follow-up and monitoring as children with these conditions have an increased risk of developing Wilms tumour.