Patient Education
What is Wilms tumor?
Wilms tumor (also called Wilms’ tumor or nephroblastoma) is a type of cancer that starts in the kidneys. It is the most common type of kidney cancer in children. It is named after Max Wilms, a German doctor who wrote one of the first medical articles about the disease in 1899.
What are Types of Wilms tumor?
Wilms tumors are grouped into 2 major types based on how they look under a microscope (their histology):
Favorable histology: Although the cancer cells in these tumors don’t look quite normal, there is no anaplasia (see next paragraph). More than 9 of 10 Wilms tumors have a favorable histology. The chance of cure for children with these tumors is very good.
Unfavorable histology (anaplastic Wilms tumor): In these tumors, the look of the cancer cells varies widely, and the cells’ nuclei (the central parts that contain the DNA) tend to be very large and distorted. This is called anaplasia. The more anaplasia a tumor has, the harder it is to cure.
What causes Wilms' tumour?
In most children, the causes of Wilms' tumor are unknown. Very rarely, people who develop Wilms' tumor have other specific conditions that are present at birth (congenital malformations). These include the lack of an iris in the eye (aniridia), abnormalities of the genitals, and a condition where one side of the body is slightly larger than the other (hemihypertrophy).
In 1 in 100 people with Wilms' tumor, another family member will also have Wilms' tumor.
What are Signs and symptoms of Wilms’ tumor?
The most common symptom is a swollen abdomen, which is usually painless. Sometimes a parent or carer may feel a lump in the abdomen which can be quite large. Occasionally, the tumor may bleed slightly and this can irritate the kidney and may be painful. There may be blood in your child's urine, or their blood pressure may be raised. The child may also have a high temperature (fever), upset stomach, weight loss, or a lack of appetite.
How Wilm’s tumour is diagnosed?
A variety of tests and investigations may be needed to diagnose a Wilms' tumor. An abdominal ultrasound scan is usually the first thing that is done. This will be followed by an MRI and/or CT scan of the abdomen and chest. These scans help doctors to identify exactly where the tumor is, and whether it has spread beyond the kidney. This is known as staging. Urine and blood samples will also be taken to check your child's kidney function and general health. Most children will go on to have a biopsy, where a sample of tissue is taken from the tumor to confirm the diagnosis.
What is staging of Wilms’ tumor?
The stage of a cancer is a term used to describe its size and whether it has spread beyond its original site. Knowing the particular type and the stage of cancer helps doctors decide on the most appropriate treatment. In the case of a Wilms’ tumor, the stage is finalized after surgery to remove the tumor. As most Wilms’ tumor patients receive chemotherapy before surgery, you may not know the exact stage of your child's tumor straight away. An exception is that babies under six months old usually have surgery straight away.
A commonly-used staging system for Wilms' tumor is described below.
Stage 1
The tumor is only affecting the kidney and has not begun to spread. It can be completely removed with surgery.
Stage 2
The tumor has begun to spread beyond the kidney to nearby structures, but it’s still possible to remove it completely with surgery.
Stage 3
The tumor has spread beyond the kidney; either because the tumor has burst before (or during) the operation, has spread to lymph glands (nodes), or has not been completely removed by surgery.
Stage 4
The tumor has spread to other parts of the body such as the lungs or liver. Tumors in other parts of the body are known as metastases.
Stage 5
There are tumors in both kidneys (bilateral Wilms' tumor).
If the tumor comes back after initial treatment, this is known as recurrent cancer or relapse.
What is treatment of Wilms’ tumour?
Treatment will depend on a number of factors including how the cells appear under the microscope (histology) and the stage of the tumor. Treatment may include chemotherapy, radiotherapy, or surgery.
Surgery
All children with Wilms’ tumor will have surgery. Initially, this may only involve taking a small sample of cells from the tumor to confirm the diagnosis. This is called a biopsy and is usually done under a general anesthetic using a needle inserted through the skin.
Apart from very young children (under six months), most patients will receive chemotherapy before having a bigger operation to remove the entire tumor. The operation usually involves removing the whole of the affected kidney (nephrectomy).
Based on the biopsy result, and after examining the whole tumor under the microscope, Wilms’ tumors can be divided into a number of groups based on knowledge about how these different types of tumors are likely to behave.
The majority of tumors are what is known as ‘standard risk’. So-called ‘low risk’ tumors require less additional treatment than standard risk tumors.
Two types of Wilms’ tumor - anaplastic and blastemal - are considered to be ‘higher risk’ than other Wilms’ tumors and require more intensive (stronger) chemotherapy.
Anaplastic Wilms’ tumor
About 5-10% of Wilms’ tumors have an appearance called anaplasia, which means the cells look very disorganized under a microscope. This is sometimes identified at biopsy, but may only be found when the whole tumor is examined after surgery.
Blastemal Wilms’ tumor
This group of high-risk tumors cannot be identified by looking at the biopsy because they occur when a particular type of early kidney cell survives the pre-surgery chemotherapy. These cells are known as blastemal cells. Tumors, where most of these cells survive chemotherapy, are called blastemal tumors.
Chemotherapy
Chemotherapy is the use of anti-cancer (cytotoxic) drugs to destroy cancer cells. It's usually given as an injection or drip into a vein (intravenously). Chemotherapy is given before surgery is called neoadjuvant chemotherapy.
What doctors find out about the tumor after surgery - for example how the cells look under the microscope and how far cancer has spread - helps them decide whether additional chemotherapy should be given (adjuvant chemotherapy). This is to help reduce the risk of cancer coming back (recurring).
Radiotherapy
Radiotherapy treats cancer by using high-energy rays to destroy the cancer cells while doing as little harm as possible to normal cells.
Not all children with Wilms’ tumor need radiotherapy. For those that do, the area to be treated depends on the stage of the tumor at diagnosis. Some children receive radiotherapy to the area around the affected kidney or to the whole abdomen. If the tumor has spread to the lungs then lung radiotherapy may be needed, but this depends on how well cancer responds to initial chemotherapy: it’s not always needed.
Radiotherapy may occasionally be used to shrink tumors that are too large to remove surgically. This will, ideally, allow an operation to be done. Radiotherapy can also be used when tumors have spread elsewhere in the body.
What is prognosis?
Most children with Wilms' tumor are cured. If cancer comes back, it's usually within the first two years. When one kidney is removed, the other will be able to work normally and can take over the work of the other kidney.
Very few children have long-term kidney problems. Your child will have regular check-ups to look for any recurrence.