What is Wilms tumor
Wilms tumor, or nephroblastoma, is a malignant tumor originating in the kidney. It can affect one or both kidneys, occurring mainly before the age of 6. For every ten cases of kidney cancer in children, nine are Wilms tumors, making this renal neoplasm the most common in childhood.
Most of the time, there is only a single isolated lesion; however, a small number of patients with Wilms tumor present with more than one tumor lesion in the same kidney. In both cases, the disease usually becomes very large before it is noticed.
Subtypes of Wilms tumor
Wilms tumors present histopathological characteristics that have implications for prognosis:
- Favorable histology – neoplastic cells do not exhibit signs of anaplasia. Approximately nine out of ten Wilms tumors have favorable histology. The chance of curing children with these tumors is very good; and
- Unfavorable histology – in these tumors, the appearance of cancer cells varies widely, and their nuclei (the parts containing the DNA) tend to be very large and distorted – this is called anaplasia. Generally, tumors in which anaplasia is spread throughout the tumor (diffuse anaplasia) are more difficult to treat than tumors in which anaplasia is limited to certain parts of the tumor (focal anaplasia).
Symptoms and signs of Wilms tumor
Wilms tumor symptoms can develop without causing any noticeable signs. Typically, its first sign is a palpable mass or swelling in the abdomen, which is generally painless.
Other symptoms associated with Wilms tumor, as it grows, include:
- Fever;
- Nausea;
- Loss of appetite;
- Shortness of breath;
- Constipation; and
- Blood in the urine.
Diagnosis of Wilms tumor
As many of the signs and symptoms of Wilms tumor are common in other pathologies, the diagnosis can take some time.
When the specialist doctor suspects the neoplasm in the clinical examination, they proceed with other steps to confirm the disease. The investigation begins with imaging tests which, most of the time, provide enough information to confirm the diagnosis. The most commonly used are:
- Abdominal Ultrasound / Total Abdominal Computed Tomography – it is one of the most useful tests to detect a tumor in the kidney. It also helps to check if the neoplasm has grown into nearby veins or spread to other organs, such as the lungs;
- Magnetic Resonance Imaging – it can be done if the doctor needs very detailed images of the kidney or nearby areas. It can also be used to look for possible spread of cancer to the brain or spinal cord;
- Chest X-ray / Chest CT – also used to detect any spread of Wilms tumor to the lungs.
- Laboratory tests, especially urine and blood tests, should be performed if the doctor suspects renal neoplasia. Urine can be tested for substances called catecholamines, which helps to make the differential diagnosis of neuroblastoma, another type of tumor that can also occur in the abdomen.
Treatment for Wilms tumor
Most children with Wilms tumor receive more than one type of treatment. Surgery is usually the first option. It should be performed by a surgeon.
- The surgery: should be performed by a surgical oncologist experienced in pediatric neoplasms, and its main goal is to remove the entire tumor in one piece, preventing neoplastic cells from spreading in the abdomen. The surgery is performed after four or six sessions of chemotherapy according to the renal tumor protocol of the International Society of Pediatric Oncology (SIOP).
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 involves the removal of the kidney, surrounding adipose tissue, and the ureter (tube that transports urine from the kidney to the bladder):
- 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 renal tissue. Only part of the kidney or kidneys is removed, but it is also possible that the kidney with the majority of the tumor may need a radical nephrectomy;
- Placement of a central venous catheter – when chemotherapy is needed as part of the treatment, a small central venous catheter is inserted into a large blood vessel, usually under the collarbone, during the tumor removal surgery. A surgery may also be performed solely for this purpose.
Chemotherapy consists of using medications 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 neoplasms. Most children with Wilms tumor will undergo chemotherapy.
Before each chemotherapy session, blood tests are done to check the levels of blood cells and whether the liver and kidney function is adequate. In case of abnormalities, chemotherapy may be postponed or doses reduced. Chemotherapeutic medications can affect cells beyond neoplastic ones and cause side effects such as hair loss, mouth sores, loss of appetite, nausea, vomiting, diarrhea, and constipation.
Radiation therapy, on the other hand, is usually part of the treatment for advanced Wilms tumors or those with unfavorable histology (anaplastic), as directed by the protocol. Generally, when indicated, it is used after nephrectomy (to eliminate cancer cells that may have remained). Before starting radiation therapy sessions, measurements are taken with imaging exams to determine the appropriate doses and correct angles for directing the radiation beams.
The possible short-term adverse effects of radiation therapy can vary from mild local changes, such as redness in the skin, to more severe skin reactions. It can also cause nausea, diarrhea, and fatigue.
Prevention of Wilms tumor
The cause of Wilms tumor is still unknown. Although some clinical conditions and genetic syndromes may be associated with a higher risk of developing the disease, to date no connection has been found with environmental factors, either during pregnancy or after the child’s birth. Therefore, there is no way to prevent the onset of this type of tumor. In cases of patients with recognized genetic syndromes (Beckwith-Wiedemann, Denys-Drash, WAGR, among others) associated with the risk of Wilms tumor, it is the duty of the pediatrician to indicate the performance of total abdominal ultrasound every 3 to 4 months until the age of 6 to 7 years.
