What Are Kidney Tumors?
Kidney tumors begin from cells in the kidneys.
The kidneys are a pair of bean-shaped organs located toward the back near the bottom of the rib cage.
Kidneys filter blood, taking out waste products and substances that are not needed. The result is urine, which is stored in the bladder until it passes out of the body.
Kidney tumors are not a common form of cancer in children.
In the United States, doctors diagnose about 550 cases each year in children younger than age 15. There are about 60 million children younger than age 15 in the United States.
The most common form of kidney tumors in children is a type of cancer called Wilms tumor.
A Wilms tumor sometimes starts when the kidneys are forming in a fetus. Some of the kidney cells begin to grow quickly out of control, forming a mass. In most cases, only one kidney has this type of mass, but sometimes both kidneys do.
Based on the look of the Wilms tumor cells, doctor may put the tumor into one of two subtypes:
- If the nuclei or "command centers" of the cells look normal, doctors say the tumor has favorable histology. About 95% of Wilms tumors fit into this subtype, which means they are easier to cure.
- If the nuclei of the cells look much larger than normal and do not have a normal shape, doctors say the tumor has unfavorable histology.
Types of Kidney Tumors
The next most common types of kidney tumor in children are:
- Renal cell carcinoma
- Clear cell carcinoma
- Rhabdoid tumor
Clear cell sarcoma is more likely than Wilms tumor to spread widely around the body, such as to the lungs, brain or bones. It is also more likely than Wilms tumor to come back after treatment.
Kidney Tumors in Children
Doctors do not know what causes kidney tumors.
Wilms tumor can run in families, so some children may be at higher risk because of genes passed down from their parents.
Doctors now believe that there are a number of genes that cause Wilms tumor, and they are working to figure out which genes they are. Most often doctors find the tumors in children around 3 years of age.
Older children are less likely to get Wilms tumor. After age 6, these tumors are rare.
Doctors diagnose renal cell carcinomas most often in 15- to 19-year-olds, clear cell sarcoma most often in the first four years of life, and rhabdoid tumors most often in infants.
Kidney Tumor Stages
Staging refers to the way doctors classify cancer based on various factors. The staging system is different for each type of cancer. Some cancer is staged only after surgery.
Children who have Wilms tumor are considered to be at one of these stages:
Stage 1 Wilms tumors
The tumor did not go beyond the capsule that surrounds the kidney, and doctors were able to take it all out with surgery.
Stage 2 Wilms tumors
The tumor went beyond the capsule that surrounds the kidney, but it appears doctors were able to take it all out with surgery. The cancer may have grown into nearby blood vessels or fat, or some may have gotten into the area near the kidney during surgery. Wilms tumors tend to be soft and can open before or during surgery.
Stage 3 Wilms tumors
Doctors could not remove the entire tumor, but the cancer that is left is only in the abdomen. For example:
- Cancer may be in the lymph nodes in the area.
- Cancer cells may remain in the body at the edge of the tissue that doctors removed.
- Cancer cells may have gotten into the abdomen before or during surgery, not only near the kidney.
- Cancer may have grown into nearby organs or other structures so that the doctor could not take it all out.
- Doctors may find tumor growth in the membrane that lines the abdomen.
Stage 4 Wilms tumors
The cancer has spread through the blood to sites far from the kidneys.
Stage 5 Wilms tumors
Both kidneys have tumors.
Other types of kidney tumors have their own staging systems. Your child's doctor can tell you about the system used for your child's cancer.
Kidney Tumors at Seattle Children's
Our doctors and other members of your child's team have worked with many children with kidney tumors. It's important to work with doctors who have experience treating this type of cancer. We can offer the latest treatments for your child.
We take part in research studies called clinical trials that are run by the Children's Oncology Group (COG).
COG is an international organization of childhood cancer specialists who conduct studies on many forms of childhood cancer. COG studies are based on the latest understanding of what causes kidney tumors. They allow us to offer the newest treatments being developed.
Kidney cancer survival rates
Doctors who treat people with cancer use five-year survival rates as one way to measure treatment success. The five-year survival rate means the percentage of patients with the disease who are alive five years after their disease was diagnosed. Outcomes for Wilms tumor treated at our center are up to 9 points better than the national average
Wilms tumor with the favorable histology subtype has a 90% to 98% survival rate. Wilms tumor with the unfavorable histology subtype has a survival rate between 60% and 80%.
Outcomes for the other types of kidney cancer tend to be worse than for Wilms tumor. We keep working with other researchers to create treatments that work better.
The survival rate for renal cell carcinoma is based on a very small number of patients and is about 83%. For clear cell sarcoma the survival rate is 85%, and for rhabdoid tumor it is 17%.
Read more about cancer programs and services and research at Children's.