Wilms Tumor Cancer (Nephroblastoma)
Also known as nephroblastoma, Wilms tumor is a type of childhood cancer that begins growing in the kidneys. The kidneys are two bean-shaped organs located towards the lower back of the rib cage, with one on each side of the body. The kidneys’ primary responsibility is to filter the blood in order to remove excess water, salt, and waste, secreting these substances as urine. Their secondary function is to ensure that the blood stays healthy by: (1) helping to control blood pressure through the production of the hormone renin; and (2) helping to maintain an appropriate supply of red blood cells through the production of the hormone erythropoietin, which tells the bone marrow to produce additional red blood cells when necessary.
There are more than 10 different types of kidney cancer in children, but Wilms tumor is by far the most common. Wilms tumor comprises about 6-7% of all childhood cancers and about 90% (9 out of 10) of all childhood kidney cancers. There are about 450-500 new cases of Wilms tumor diagnosed each year in the United States, occurring slightly more frequently in girls than in boys. Wilms tumor is most frequently diagnosed in children between the ages of 3 and 4, and is quite uncommon after the age of 6.
In about 95% of diagnoses, Wilms tumor is unilateral, which means that the tumor is confined to only one kidney; however, in about 5-10% of these diagnoses, there are multiple tumors within the same kidney. About 5% of children are diagnosed with bilateral Wilms tumor, which means that there are tumors in both kidneys. Although Wilms tumors are usually not diagnosed until they have grown quite large—the most common symptom is a hard lump or swelling on the abdomen—most Wilms tumors are diagnosed before they have metastasized (spread) to other organs or areas of the body.
Types of Wilms Tumors and Four-Year Survival Rates Based on Type
Once Wilms tumor has been diagnosed, the cancerous cells are examined under a microscope to determine their histology. This will help determine the severity of the disease as well as the appropriate course of treatment. Wilms tumors are classified as two different types depending on their histology:
- Favorable: more than 9 out of every 10 case of Wilms tumor has a favorable histology, meaning the tumor shows no signs of anaplasia (enlarged, distorted cell nuclei).
- Unfavorable: also called anaplastic Wilms tumor. When a Wilms tumor is unfavorable, the appearance of the cancerous cells varies widely, with most cells showing very large and distorted nuclei, or anaplasia. The more anaplasia the tumor shows, the more difficult it is to treat effectively.
Statistics for Wilms tumor are given as four-year survival rates, or the percentage of children who live at least four years after their initial diagnosis with Wilms tumor. It is important to note that these statistics are averages only; they do not indicate the prognosis for any particular child. Your child’s prognosis depends on many factors, including your child’s overall health, the course of treatment, and the tumor’s response to that treatment. If your child has been diagnosed with Wilms tumor, it is important that you speak with your oncology team about the details of your child’s diagnosis.
Statistics for four-year survival rates for Wilms tumor are based on both the histology and stage of the tumor, or how much the tumor has grown. The four-year survival rates for Wilms tumor with a favorable histology range from 99% for Stage 1 tumors to about 87% for Stage V tumors. However, the four-year survival rates decline significantly for anaplastic Wilms tumors: about 83% for Stage 1 and declining precipitously to 55% for Stage V.
About American Childhood Cancer Organization
American Childhood Cancer Organization (ACCO) is a non-profit charity dedicated to helping kids with cancer and their families navigate the difficult journey from cancer diagnosis through survivorship. Internationally, ACCO is the sole U.S. member of Childhood Cancer International (CCI), the largest patient-support organization for childhood cancer in the world. Here in the United States, ACCO promotes the critical importance of ensuring continued funding into new and better treatment protocols for childhood cancer. And most importantly, ACCO is focused on the children: developing and providing educational tools for children fighting cancer and their families, empowering them in their understanding of childhood cancer and the medical decisions they must make during this difficult journey. All of ACCO’s resources are available free of charge for families coping with childhood cancer.