What is Wilms Tumor
Wilms tumor, or nephroblastoma, is a malignant tumor that originates in the kidney. It can affect one or both kidneys, occurring mainly before 6 years of age. Nine out of ten cases of kidney cancer in children are Wilms tumors, which makes this kidney cancer the most common in childhood.
Most of the time, there is only one isolated lesion; a small number of patients with Wilms tumor, however, have more than one tumor lesion in the same kidney. In either case, the disease usually becomes very large before it is noticed.
Wilms tumor subtypes
Wilms tumors are grouped into two main types based on their appearance under the microscope, called histology:
- Favorable histology – the neoplastic cells do not look very normal, but there is no anaplasia. Approximately nine out of ten Wilms tumors have a favorable histology. The chance of curing children with these tumors is very good; and
- Anaplastic histology – in these tumors, the appearance of cancer cells varies widely and their nuclei (the parts that contain the DNA) tend to be very large and distorted – this is called anaplasia. In general, tumors in which the anaplasia is spread throughout the tumor (diffuse anaplasia) are more difficult to treat than tumors in which the anaplasia is limited to only certain parts of the tumor (focal anaplasia).
Wilms tumor symptoms and signs
Wilms’ tumor can develop without causing any symptoms. Your first sign is usually a palpable mass or swelling in your abdomen, which is usually not painful.
Other symptoms associated with Wilms tumor as it grows are:
- Loss of appetite;
- Shortness of breathe;
- Constipation; and
- Blood in the urine.
Wilms tumor diagnosis
As many of the signs and symptoms of Wilms tumor are common in other conditions, diagnosis can take a while.
When the specialist doctor suspects the neoplasm on clinical examination, he proceeds with other steps to confirm the disease. The investigation begins with imaging tests, which, in most cases, provide enough information to confirm the diagnosis. The most used are:
- CT scan – this is one of the most useful tests to detect a kidney tumor. It also helps to check whether the tumor has grown into nearby veins or has spread to other organs, such as the lungs;
- MRI – this may be done if the doctor needs very detailed images of the kidney or nearby areas. It can also be used to look for a possible spread of cancer to the brain or spinal cord;
- Chest X-ray – also used to detect any spread of Wilms tumor to the lungs. In more advanced stages of treatment, it is used to detect changes in the disease (positive or negative).
Laboratory tests, especially urine and blood tests, should be performed if the doctor suspects kidney cancer. Urine can be tested for substances called catecholamines, which helps make the differential diagnosis from neuroblastoma, another type of tumor that can also occur in the abdomen.
When tests indicate the presence of Wilms’ tumor, the diagnosis must be made through biopsy, with the removal of a sample of the tumor for analysis. At this stage, pathologists also identify the histology of the disease.
Most children with Wilms tumor receive more than one type of treatment.
Surgery is usually the first option. It must be performed by an oncological surgeon with experience in pediatric neoplasms, and its main objective is to remove the entire tumor in one piece, preventing neoplastic cells from spreading in the abdomen. If at the time of diagnosis it is not possible to remove the entire tumor, other treatments can be used to reduce its dimensions and allow the surgery to be performed later, more safely.
Depending on the situation, different types of surgeries can be performed:
- Radical nephrectomy – is the most common surgery for Wilms tumor located in only one kidney. It removes the kidney, the adrenal gland that sits on top of the kidney, the surrounding fatty tissue, and the ureter (the tube that carries urine from the kidney to the bladder). Most children do not have any health problems with having only one kidney;
- Partial nephrectomy (nephron-sparing surgery) – indicated for the small number of children with Wilms tumors in both kidneys, this surgery attempts to preserve some normal kidney tissue. Only part of the kidney or kidneys is removed, but it is also possible that the kidney with the most tumor will need to undergo a radical nephrectomy;
- Exploratory surgery – when radical or partial nephrectomy is done, another goal of surgery is to determine the extent of the neoplasm and whether or not it can be removed. This type of cancer can spread to the lymph nodes, which makes it necessary to remove the lymph nodes near the kidney. Removing the lymph nodes is called a lymphadenectomy. In addition, any suspicion that another nearby organ, such as the liver, may have been affected by the cancer is investigated during surgery. In this case, samples are taken for later biopsy; and
- Placement of a central venous catheter – when chemotherapy is required to continue treatment, a small central venous catheter is inserted into a large blood vessel, usually under the collarbone, during surgery to remove the tumor. Surgery may also be performed for this purpose alone.
Chemotherapy is the use of drugs infused into the bloodstream to reach all areas of the body, including and especially the tumor. It is a very useful treatment for localized and bulky disease, as well as for disseminated neoplasia. Most children with Wilms tumor will have chemotherapy at some point.
Before each chemotherapy session, blood tests are done to check your blood cell levels and that your liver and kidneys are functioning properly. In case of abnormality, chemotherapy may be delayed or doses reduced.
Chemotherapy drugs can affect cells in addition to cancer cells and cause side effects such as hair loss, canker sores, loss of appetite, nausea, vomiting, diarrhea and constipation.
Radiation therapy, in turn, is usually part of the treatment for more advanced Wilms tumors (stages III, IV and V), as well as for some tumors in early stages with anaplastic histology. It can be used after surgery (to eliminate any remaining cancer cells), before surgery (to shrink the tumor, making it easier to remove), or even in place of surgery (if surgery cannot be done for some reason).
Before the beginning of the radiotherapy sessions, measurements are made with imaging tests to determine the appropriate doses and the correct angles for directing the radiation beams.
Possible short-term adverse effects of radiation therapy can range from mild local changes, such as skin redness, to more severe skin reactions. It can also cause nausea, diarrhea and tiredness.
The cause of Wilms’ tumor is still unknown. Although some clinical conditions and genetic syndromes may be associated with an increased risk of developing the disease, to date, a link to environmental factors has not been found, either during pregnancy or after childbirth. There is, therefore, no way to prevent the emergence of this type of tumor.