Cancers that develop in children are often different from those that develop in adults. Childhood cancers are often the result of DNA changes in cells very early in life, sometimes even before birth. Unlike many cancers in adults, childhood cancers are not strongly linked to lifestyle or environmental risk factors.

There are exceptions, but childhood cancers tend to respond better to treatments such as chemotherapy. Children’s bodies also tend to tolerate chemotherapy better than adults’ bodies do. But cancer treatments such as chemotherapy and radiation therapy can have some long-term side effects, so children who have had cancer need careful attention for the rest of their lives.

Since the 1960s, most children and teens with cancer have been treated at specialized centers designed for them. These centers offer the advantage of being treated by a team of specialists who know the differences between adult and childhood cancers, as well as the unique needs of children with cancer and their families. This team usually includes pediatric oncologists (childhood cancer doctors), surgeons, radiation oncologists, pathologists, pediatric oncology nurses, and nurse practitioners. These centers also have psychologists, social workers, child life specialists, nutritionists, rehabilitation and physical therapists, and educators who can support and educate the entire family.

Most children with cancer in the United States are treated at a center that is a member of the Children’s Oncology Group (COG). All of these centers are associated with a university or children’s hospital. As we have learned more about treating childhood cancer, it has become even more important that treatment be given by experts in this area.

Any time a child or teen is diagnosed with cancer, it affects every family member and nearly every aspect of the family’s life. You can read more about coping with all these changes in Children Diagnosed With Cancer: Dealing With Diagnosis.

Survival rates are often used by doctors as a standard way of discussing a person’s prognosis (outlook). Some parents may want to know the survival statistics for children in similar situations, while others may not find the numbers helpful, or may even not want to know them. If you would rather not read about survival rates, don’t read any further.

The 4-year survival rate refers to the percentage of children who live at least 4 years after their cancer is diagnosed. Of course, many children live much longer than 4 years (and many are cured).

To get 4-year survival rates, doctors have to look at children who were treated at least 4 years ago. Improvements in treatment since then may result in a better outlook for children now being diagnosed with Wilms tumors.

These survival rates are based on the results of the National Wilms Tumor Studies, which included most of the children treated in the United States in the last few decades. The most important factors in determining a child’s outlook are the stage and histology of the tumor. (Histology refers to how the cancer cells look under the microscope – see What is Wilms tumor?) Some of these rates are based on only small numbers of children, so it’s hard to know if they are accurate.

Survival rates are based on previous outcomes of children who had the disease, but they can’t predict what will happen in any particular child’s case. Knowing the stage and histology of a Wilms tumor are important in estimating the child’s outlook. But other factors can also affect a child’s outlook, such as how well the tumor responds to treatment. Even when taking other factors into account, survival rates are only rough estimates. Your child’s doctor can tell you if the numbers below apply, as he or she knows your child’s situation best.

The stage of a cancer describes how far it has spread. Your child’s treatment and prognosis (outlook) depend, to a large extent, on the cancer’s stage. Staging is based on the results of the physical exam and imaging tests (ultrasound, CT scans, etc.), which are described in How are Wilms tumors diagnosed?, as well as on the results of surgery to remove the tumor, if it has been done.

Children’s Oncology Group (COG) staging system

A staging system is a standard way for the cancer care team to sum up the extent of the tumor. In the United States, the Children’s Oncology Group staging system is used most often to describe the extent of spread of Wilms tumors. This system describes Wilms tumor stages using Roman numerals I through V (1 through 5).

Stage I

The tumor was contained within one kidney and was removed completely by surgery. The tissue layer surrounding the kidney (the renal capsule) was not broken during surgery. The cancer had not grown into blood vessels in or next to the kidney. The tumor was not biopsied before surgery to remove it.

About 40% to 45% of all Wilms tumors are stage I.

Stage II

The tumor has grown beyond the kidney, either into nearby fatty tissue or into blood vessels in or near the kidney, but it was removed completely by surgery without any apparent cancer left behind. Nearby lymph nodes (bean-sized collections of immune cells) do not contain cancer. The tumor was not biopsied before surgery.

About 20% of all Wilms tumors are stage II.

Stage III

This stage refers to Wilms tumors that may not have been removed completely. The cancer remaining after surgery is limited to the abdomen (belly). One or more of the following features may be present:

• The cancer has spread to lymph nodes in the abdomen or pelvis but not to more distant lymph nodes, such as those inside the chest.
• The cancer has grown into nearby vital structures so the surgeon could not remove it completely.
• Deposits of tumor (tumor implants) are found along the inner lining of the abdominal space.
• Cancer cells are found at the edge of the sample removed by surgery, a sign that some of the cancer still remains after surgery.
• Cancer cells “spilled” into the abdominal space before or during surgery.
• The tumor was removed in more than one piece – for example, the tumor was in the kidney and in the nearby adrenal gland, which was removed separately.
• A biopsy of the tumor was done before it was removed with surgery.

About 20% to 25% of all Wilms tumors are stage III.

Stage IV

The cancer has spread through the blood to organs away from the kidneys such as the lungs, liver, brain, or bones, or to lymph nodes far away from the kidneys.

About 10% of all Wilms tumors are stage IV.

Stage V

Tumors are found in both kidneys at diagnosis.

About 5% of all Wilms tumors are stage V.

Tumor histology

The other main factor in determining the prognosis and treatment for a Wilms tumor is the tumor’s histology, which is based on how the tumor cells look under a microscope. The histology can be either favorable or unfavorable (anaplastic). These are described in more detail in What is Wilms tumor?

Wilms tumors can be hard to find early because they can often grow quite large without causing any symptoms. Children may look healthy and play normally.

Swelling or a hard mass in the abdomen (belly): This is often the first sign of a Wilms tumor. Parents may notice this while bathing or dressing the child. It feels firm and is often large enough to be felt on both sides of the belly. It’s usually not painful, but it might cause belly pain in some children.

Other possible symptoms: Some children with Wilms tumor may also have:

• Fever
• Nausea
• Loss of appetite
• Shortness of breath
• Constipation
• Blood in the urine

Wilms tumors can also sometimes cause high blood pressure. This does not usually cause symptoms on its own, but in rare cases blood pressure can get high enough to cause problems such as headaches, bleeding inside the eye, or even a change in consciousness.

Many of the signs and symptoms above are more likely to be caused by something other than a kidney tumor. Still, if your child has any of these symptoms, check with your child’s doctor so that the cause can be found and treated, if needed.

Each year, about 500 new cases of Wilms tumors are diagnosed in the United States. This number has been fairly stable for many years. About 5% of all cancers in children are Wilms tumors.

Wilms tumors tend to occur in young children. The average age at diagnosis is about 3 to 4 years. It becomes less common as children grow older and is uncommon after age 6. It’s very rare in adults, although cases have been reported.

Statistics related to survival for Wilms tumors are discussed in the section “ Survival rates for Wilms tumor, by stage and histology.”

Visit the American Cancer Society’s Cancer Statistics Center for more key statistics.

Because of major advances in treatment, most children treated for Wilms tumor are now surviving into adulthood. Doctors have learned that treatment can affect children’s health later in life, so watching for health effects as they get older has become more of a concern in recent years. We have information to help parents cope with the many issues that can come up during and after a child is treated for cancer.

Just as the treatment of childhood cancer requires a very specialized approach, so does the care and follow-up after treatment. The earlier any problems can be recognized, the more likely it is they can be treated effectively. Young people treated for Wilms tumor are at risk, to some degree, for several possible late effects of their cancer treatment. It’s important to discuss what these possible effects might be with your child’s medical team so you know what to watch for and report to the doctor.

The risk of late effects depends on a number of factors, such as the specific treatments the child has, the doses of treatment, and the age of the child when being treated. These late effects may include:

• Reduced kidney function
• Heart or lung problems after getting certain chemotherapy drugs or radiation therapy to these parts of the body
• Slowed or delayed growth and development
• Changes in sexual development and ability to have children, especially in girls
• Increased risk of second cancers later in life (rare)

There may be other possible complications from treatment as well. Your child’s doctor should carefully review any possible problems with you before your child starts treatment.

Along with physical side effects, some childhood cancer survivors might have emotional or psychological issues. They might also have problems with normal functioning and school work. These can often be addressed with support and encouragement. If needed, doctors and other members of the health care team can recommend special support programs and services to help children after cancer treatment.

Long-term follow-up care

To help increase awareness of late effects and improve follow-up care of childhood cancer survivors throughout their lives, the Children’s Oncology Group (COG) has developed long-term follow-up guidelines for survivors of childhood cancers. These guidelines can help you know what to watch for, what type of screening tests should be done to look for problems, and how late effects can be treated.

Ask your child’s health care team about possible long-term complications and make sure there’s a plan in place to watch for these problems and treat them, if needed. To learn more, ask your child’s doctors about the COG survivor guidelines. You can also read them online at www.survivorshipguidelines.org. You may want to discuss them with your child's doctor.

Children Diagnosed With Cancer: Late Effects of Cancer Treatment tells you a lot more about some of the possible long-term effects of cancer treatment. 

Things to keep

As much as you might want to put the experience behind you once treatment is completed, it’s very important to keep good records of your child’s medical care during this time. This can be very helpful later on as your child changes doctors. Gathering these details during and soon after treatment may be easier than trying to get them in the future. 

It’s also very important to keep health insurance coverage. Follow-up tests and doctor visits cost a lot, and even though no one wants to think of the tumor coming back, this could happen.

A risk factor is anything that affects the chance of having a disease such as cancer. Different cancers have different risk factors.

Lifestyle-related risk factors such as body weight, physical activity, diet, and tobacco use play a major role in many adult cancers. But these factors usually take many years to influence cancer risk, and they are not thought to have much of an effect on the risk of childhood cancers, including Wilms tumors.

So far research has not found any strong links between Wilms tumor and environmental factors, either during a mother’s pregnancy or after a child’s birth.

Most Wilms tumors have no clear cause, but there are some factors that affect risk.

Age

Wilms tumors are most common in young children, with the average age being about 3 to 4 years. They are less common in older children, and rare in adults.

Race

In the United States, the risk of Wilms tumor is slightly higher in African-American children than in white children and is lowest among Asian-American children. The reason for this is not known.

Gender

Girls have a slightly higher risk of Wilms tumor than boys.

Family history of Wilms tumor

About 1% to 2% of children with Wilms tumors have one or more relatives with the same cancer. Scientists think that these children inherit chromosomes with an abnormal or missing gene from a parent that increases their risk of developing Wilms tumor. Surprisingly, the relative with Wilms tumor is not usually a parent.

Children with a family history of Wilms tumors are slightly more likely to have tumors in both kidneys. Still, in most children only one kidney is affected.

Certain genetic syndromes/birth defects

There is a strong link between Wilms tumors and certain kinds of birth defects. About 1 child in 10 with Wilms tumor also has birth defects. Most birth defects linked to Wilms tumors occur in syndromes. A syndrome is a group of symptoms, signs, malformations, or other abnormalities that occur together in the same person. Syndromes linked to Wilms tumor include:

WAGR syndrome

WAGR stands for the first letters of the physical and mental problems linked with this syndrome (although not all children have all of them):

• Wilms tumor
• Aniridia (complete or partial lack of the iris [colored area] of the eyes)
• Genitourinary tract abnormalities (defects of the kidneys, urinary tract, penis, scrotum, clitoris, testicles, or ovaries)
• Mental Retardation

Children with this syndrome have about a 30% to 50% chance of having a Wilms tumor. The cells in children with WAGR syndrome are missing part of chromosome 11, where the WT1 gene is normally found (see Do we know what causes Wilms tumors?). Children with WAGR tend to get Wilms tumors at an earlier age and often have tumors in both kidneys.

Denys-Drash syndrome and Frasier syndrome

These rare syndromes have also been linked to changes (mutations) in the WT1 gene.

In Denys-Drash syndrome, the kidneys become diseased and stop working when the child is very young. Wilms tumors usually develop in the diseased kidneys. The reproductive organs don’t develop normally, and boys may be mistaken for girls. Because the risk of Wilms tumors is very high, doctors often advise removing the kidneys soon after this syndrome is diagnosed.

In Frasier syndrome the kidneys are also diseased, but they usually keep working into adolescence. As with Denys-Drash syndrome, the reproductive organs don’t develop normally. Children with Frasier syndrome are also at increased risk for Wilms tumors, although they are at even higher risk for cancers in the reproductive organs.

Beckwith-Wiedemann syndrome

Children with this syndrome tend to be big for their age. They also have larger than normal internal organs and often have an enlarged tongue. They may have an oversized arm and/or leg on one side of the body (called hemihypertrophy), as well as other medical problems. They have about a 5% risk of having Wilms tumors (or, less often, other cancers that develop during childhood). This syndrome is caused by a defect in chromosome 11 that affects the WT2 gene.

Other syndromes

Less often, Wilms tumor has been linked to other syndromes, including:

• Perlman syndrome
• Sotos syndrome
• Simpson-Golabi-Behmel syndrome
• Bloom syndrome
• Li-Fraumeni syndrome
• Trisomy 18

Certain birth defects

Wilms tumor is also more common in children with certain birth defects (without known syndromes):

• Aniridia (complete or partial lack of the iris [colored area] of the eyes)
• Hemihypertrophy (an oversized arm and/or leg on one side of the body)
• Cryptorchidism (failure of the testicles to descend into the scrotum) in boys
• Hypospadias (defect in boys where the urinary opening is on the underside of the penis)

Although there is a clear link between Wilms tumors and certain birth defect syndromes and genetic changes, most children with this type of cancer do not have any known birth defects or inherited gene changes.

Researchers do not yet know exactly why some children get Wilms tumors, but they have made great progress in understanding how normal kidneys develop, as well as how this process can go wrong, leading to a Wilms tumor.

The kidneys develop very early as a fetus grows in the womb. Changes (mutations) in certain genes in early kidney cells can lead to problems as the kidneys develop. Some of the cells that are supposed to develop into mature kidney cells stay as early kidney cells instead. Clusters of these early kidney cells sometimes remain after the baby is born. Usually, these cells mature by the time the child is 3 to 4 years old. If this doesn’t happen, the cells might somehow begin to grow out of control, which might result in a Wilms tumor.

Normal human cells grow and function based mainly on the information contained in each cell’s chromosomes (long strands of DNA in each cell). DNA carries the instructions for nearly everything our cells do. DNA is divided into units called genes.

Some genes control when our cells grow, divide into new cells, and die. Genes that help cells grow, divide, or stay alive are called oncogenes. Others that slow down cell division or cause cells to die at the right time are called tumor suppressor genes. Cancers can be caused by DNA changes that turn on oncogenes or turn off tumor suppressor genes. These gene changes can be inherited from a parent (as is sometimes the case with childhood cancers), or they may happen during a person’s lifetime as cells in the body divide to make new cells.

Changes in certain genes increase the chance that some kidney cells will remain in an early form and turn into a Wilms tumor.

For example, a small number of Wilms tumors are caused by changes (mutations) in or loss of the WT1 or WT2 genes, which are tumor suppressor genes found on chromosome 11. Changes in these genes and some other genes on chromosome 11 can lead to overgrowth of certain body tissues. This may explain why some other growth abnormalities, like those described in the section What are the risk factors for Wilms tumor? are sometimes found with Wilms tumors.

Sometimes these gene changes are passed on from a parent to a child, but most Wilms tumors don’t seem to be caused by inherited gene mutations. Instead, they seem to result from gene changes that occur early in a child’s life, perhaps even before birth.

In a small number of Wilms tumors there is a change in a tumor suppressor gene known as WTX, which is found on the X chromosome. Another gene that is sometimes altered in Wilms tumor cells is known as CTNNB1. It’s not clear exactly what causes these genes to be altered.

Because the genes described above are not altered in all Wilms tumors, there must be gene changes that have not yet been found. In many cases, more than one gene change is involved.

Researchers now understand some of the gene changes that can occur in Wilms tumors, but it’s still not clear what causes these changes. Some gene changes can be inherited, but most Wilms tumors are not the result of known inherited syndromes. Other gene changes may just be random events that sometimes happen inside a cell, without having an outside cause. There are no known lifestyle-related or environmental causes of Wilms tumors, so it is important to know that there is nothing these children or their parents could have done to prevent these cancers.

Wilms tumors are usually found when they start to cause symptoms such as swelling in the abdomen (belly), but by this point they have often grown quite large. They can be found earlier in some children with tests such as an ultrasound of the abdomen. (See the section How are Wilms tumors diagnosed?”) But because Wilms tumors are rare, it’s not practical to use ultrasound exams as a screening test (a test to look for disease in people with no signs or symptoms) in all children who are not at increased risk. There are no blood tests or other tests that are useful in screening otherwise healthy children for Wilms tumors.

On the other hand, screening for Wilms tumor is very important for children who have syndromes or birth defects known to be linked to this disease. For these children, most doctors recommend physical exams by a specialist and ultrasound exams on a regular basis (for example, about every 3 or 4 months at least until the age of 8) to find any kidney tumors when they are still small and have not yet spread to other organs.

Wilms tumor can also run in families, although this is rare. Talk to your doctor if you have any relatives who have had a Wilms tumor. If you do, the children in your family may need to have regular ultrasound exams of the abdomen. If a man or woman is known to have a WT1 gene mutation, testing can be done to see if they have passed the mutation on to their children. (This can be done even before birth.)

During and after treatment for Wilms tumors, the main concerns for most families are the short- and long-term effects of the tumor and its treatment, and concerns about the tumor still being there or coming back.

It’s certainly normal to want to put the tumor and its treatment behind you, and get back to a life that doesn’t revolve around cancer. But it’s important to realize that follow-up care is a central part of treatment that offers your child the best chance for long-term recovery.

Follow-up exams and tests

Your child’s health care team will set up a follow-up schedule, which will include physical exams and imaging tests (such as chest x-rays, ultrasounds, and CT scans) to look for the growth or return of the tumor, or any problems related to treatment.

Since most children have had a kidney removed, blood and urine tests will be done to check how well the remaining kidney is working. If your child received the drug doxorubicin (Adriamycin) during chemotherapy, the doctor may also order tests to check the function of your child’s heart.

The recommended schedule for follow-up exams and tests depends on the initial stage and histology (favorable or unfavorable) of the cancer, the type of treatment, and any problems that the child may have had during treatment. Doctor visits and tests will be more frequent at first (about every 6 to 12 weeks for the first couple of years), but the time between visits may be extended as time goes on.

During this time, it’s important to report any new symptoms to your child’s doctor right away, so that the cause can be found and treated, if needed. Your child’s doctor can give you an idea of what to watch for.

If the tumor does come back, or if it doesn’t respond to treatment, your child’s doctors will discuss the treatment options with you.

Children with bilateral Wilms tumors or Denys-Drash syndrome will also need regular tests to look for possible early signs of kidney failure (including urine tests, blood pressure checks, and blood tests of kidney function).