10 Facts About Wilms Tumor and Kidney Cancer in Children

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Wilms tumor, also known as nephroblastoma, is the most common form of kidney cancer in children, accounting for 9 out of 10 pediatric kidney cancers. About 75 percent of those cases are children under the age of 5. Wilms tumor is linked to certain genetic syndromes and birth defects, and although rare, it can sometimes run in families. However, most children with Wilms tumor don’t have birth defects or inherited gene mutations.


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Understanding the basics about Wilms tumor

About 500 children are diagnosed with Wilms tumor each year in the U.S., most often between 3 and 4. These tumors have often grown large before they are found, and may be much bigger than the kidney. Most Wilms tumors are found before they metastasize, or spread. Most cases involve just one kidney, but about 5 percent of cases are bilateral, with tumors in both kidneys. Although rare, adults have also been reported with Wilms tumor.


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What kind of symptoms may a child experience with Wilms tumor?

The kidneys are bean-shaped organs located near the middle of the back. They filter waste from the blood, which creates urine. Children with Wilms tumor may experience symptoms including: abdominal mass you can feel, pain, blood in urine, high blood pressure, fever, weight loss, shortness of breath, and urinary tract infections.


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How does Wilms tumor develop?

It’s unclear exactly what causes Wilms tumor, but it is believed that it begins as a small mass made from embryonic tissue that never fully developed. As a fetus grows in the womb, changes, or mutations, in certain genes in early kidney cells can lead to problems as the kidney develops. Clusters of these early kidney cells may remain in a baby after birth. If these cells don’t mature as the child grows, they may begin to grow out of control, resulting in cancer.


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Two types of Wilms tumor

There are two major types of Wilms tumors based on the type of cells found in the tumor. A doctor can determine the tumor’s histology, or cell type, by looking at a piece of it under a microscope. A favorable histology means there is no anaplasia of the cells, meaning the cells’ nuclei isn’t distorted. About 92 percent of cases have favorable histology. These cases have a good chance of being cured.


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What is an unfavorable histology?

An unfavorable histology means that when examined, the tumor cells look different and the cell’s nuclei is large and distorted. Anaplasia is resistant to chemotherapy so the more distortion there is, the harder it is to cure.


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Staging Wilms tumor

Once Wilms tumor is diagnosed, the next step is for a doctor to determine what stage the cancer is in. There are five stages of Wilms tumors which describe the extent of the cancer and how far it has advanced. For instance, stage 1 means the cancer is contained to the kidney and was completely removed with surgery. Stage 5 means both kidneys have tumors when diagnosed: read more in the next slide.


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Stage 5 Wilms tumor

Stage 5 indicates that there are tumors in both kidneys, which likely means that there was abnormal tissue on both kidneys that developed into tumors. It’s not likely that the tumor spread from one kidney to the other. Treatment for this type of cancer is based on the kidney with the more advanced stage following surgery. How many cases are in this stage? Oddly the same number as the stage itself: 5 percent.


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Treatment options for Wilms tumor

There are three main types of treatment for Wilms tumor: surgery, chemotherapy, and radiation therapy. Surgery is often the first treatment for patients in the U.S., with the goal of removing the main tumor. If the tumor is large or has spread to nearby blood vessels, the doctor may recommend chemotherapy or radiation therapy beforehand.


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Wilms tumor can develop outside of the kidneys

On rare occasions, Wilms tumor can develop outside of the kidneys, and is classified as “extrarenal.” Nearly all of the cases of Extrarenal Wilms’ tumor are reported in children, with less than 1 percent being reported in adults. Most often these tumors are found in the abdominal cavity, the groin area, in the lower back and pelvic area and in females around genital and reproductive organs such as the uterus or ovaries.


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National Wilms Tumor Study brought about many treatment advances

At the beginning of the 20th century, about 90 percent of children who were diagnosed with Wilms tumor died. By the end of the century, nearly 90 percent survived and went on to live fairly normal lives. This is in large part thanks to advances that came from clinical trials that were conducted by the National Wilms Tumor Study, which began in 1969. The study has helped doctors learn how to treat Wilms tumor more effectively.


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Continuing to look at long-term side effects

The study is continuing to look at the long-term side effects of the cancer and treatment. It aims to identify serious medical conditions that Wilms Tumor survivors may be predisposed to as they grow older, including congestive heart failure, a second malignant tumor, kidney failure, chronic lung disease, and diabetes. It's also examining if the children or siblings of patients who had Wilms tumor are at increased risk of developing the cancer themselves.