Nephroblastoma, commonly known as Wilms tumor, is a rare kidney cancer that primarily affects young children, with most cases occurring before age five. While the diagnosis can feel overwhelming for families, advances in treatment have made this one of the most successfully treatable childhood cancers.
Epidemiology
Nephroblastoma stands as the most common type of kidney cancer in children, representing nearly 90% of all pediatric kidney tumors. In the United States, approximately 500 to 650 new cases are diagnosed each year, making it a relatively rare condition overall. Despite this rarity, nephroblastoma ranks as the fourth most common cancer in children and the most frequent abdominal cancer in this age group.[1][2][3]
The disease shows a clear age pattern. Most children are diagnosed between the ages of two and five years, with the median age at diagnosis being around three to four years old. The condition becomes increasingly rare after age five, though it can occasionally affect older children and even adults. About 95% of all cases are diagnosed by the time a child reaches ten years old.[1][3]
Gender differences in nephroblastoma are relatively minor. Girls appear to be affected slightly more often than boys, though the difference is small. When it comes to ethnicity, important patterns emerge. The disease is more common in children of African and African American descent, while children of Asian heritage have the lowest rates. European and North American rates fall somewhere in between. Interestingly, Asian patients also tend to have less aggressive forms of the disease and generally experience better outcomes.[2][3]
In most cases, nephroblastoma affects only one kidney, a situation described as unilateral disease. However, in about 5% of cases, tumors develop in both kidneys at the same time, which doctors call bilateral disease. Bilateral nephroblastoma is more commonly seen in girls than boys.[2]
Causes
The exact cause of nephroblastoma remains unclear in most cases. What doctors do know is that the cancer develops when something goes wrong with the normal growth of kidney cells. During development in the womb, certain kidney cells may not mature properly as they should. These abnormal cells can remain in the kidney after birth, and in some children, they may eventually develop into a tumor.[1][4]
The root of the problem lies in genetic changes that affect how kidney cells grow and divide. Scientists have identified several genes associated with nephroblastoma. These include genes labeled WT1, CTNNB1, and WTX, which show alterations in about one-third of all cases. Other genes linked to the disease include TP53 and MYNC. When certain genetic changes occur, particularly in genes like TP53 or when parts of chromosomes are lost, the prognosis may be less favorable.[2]
During fetal development, kidneys form from special tissue called metanephric tissue. Sometimes, clusters of these immature cells persist after birth in what doctors call nephrogenic rests. These abnormal cell clusters appear in up to 1% of infant kidneys but typically disappear as children grow. However, these rests are found in nearly all children with bilateral nephroblastoma and in about 35% of those with tumors in just one kidney, suggesting they may serve as a starting point for tumor development.[2]
It’s important to note that nephroblastoma is not contagious and cannot be spread from one person to another. Unlike some infectious diseases, there is no transmission route because this is not caused by an outside organism but rather by changes within the child’s own cells.[1]
Risk Factors
While nephroblastoma can develop in any child, certain factors increase the likelihood of developing this cancer. Understanding these risk factors helps identify children who may benefit from regular screening and closer monitoring.
The strongest risk factors involve specific genetic syndromes present from birth. Children with WAGR syndrome face approximately a 50% chance of developing nephroblastoma. The name WAGR itself includes “W” for Wilms tumor, along with other features including absence of the colored part of the eye, genital abnormalities, and developmental delays. Denys-Drash syndrome carries an even higher risk, with about 90% of affected children developing nephroblastoma, along with kidney problems and genital development issues. Children with Beckwith-Wiedemann syndrome, an overgrowth condition where body parts grow larger than normal and may be asymmetric, have a 5% to 10% risk of developing nephroblastoma.[3][4]
Other genetic conditions associated with increased risk include Frasier syndrome, Perlman syndrome, and Simpson-Golabi-Behmel syndrome. Each of these conditions involves specific genetic changes that affect normal development and increase cancer susceptibility.[4]
Certain birth defects also appear more frequently in children with nephroblastoma, though these conditions don’t necessarily cause the tumor. These include aniridia (partial or complete absence of the iris), hemihypertrophy (when one side of the body grows larger than the other), cryptorchidism (undescended testicles), hypospadias (abnormal opening of the urethra), and horseshoe kidney (when the two kidneys are fused together). The presence of these conditions may prompt doctors to monitor children more closely.[2][3]
Family history plays a role in only a very small percentage of cases. Less than 1% of children with nephroblastoma have a relative who also had the disease, and typically that relative is not a parent. This means that most cases occur sporadically without any family connection.[2]
Unlike many adult cancers, nephroblastoma does not appear to be linked to lifestyle factors, environmental exposures, or behaviors. Parents should understand that nothing they did or didn’t do caused their child’s cancer.[1]
Symptoms
The signs and symptoms of nephroblastoma can vary considerably from child to child. Some children show obvious symptoms, while others appear completely healthy despite having a tumor. Understanding these symptoms helps parents recognize when medical evaluation is needed.
The most common symptom, occurring in the majority of cases, is a swelling or firm lump in the abdomen. Parents often discover this mass accidentally while bathing their child, helping them get dressed, or changing diapers. The lump typically feels smooth and firm to the touch and can sometimes grow quite large before being noticed. Some tumors become so substantial they equal or exceed the size of the kidney itself.[1][3]
Interestingly, despite the presence of a tumor, many children with nephroblastoma do not experience pain. When abdominal pain does occur, it may range from mild discomfort to more significant pain that affects the child’s daily activities and comfort.[1][3]
Blood in the urine, a condition called hematuria, appears in some children with nephroblastoma. Sometimes the blood is visible to the naked eye, making the urine appear pink, red, or cola-colored. In other cases, blood can only be detected through laboratory testing of the urine.[1][3]
Fever without an obvious cause sometimes develops in children with nephroblastoma. This fever occurs because the body’s immune system responds to the presence of the tumor. Similarly, some children develop hypertension, or high blood pressure. When blood pressure rises significantly, it can cause additional symptoms including nosebleeds, headaches, and even visible blood in the white part of the eye.[1][3]
General symptoms may also appear. Children might show decreased appetite and become less interested in eating their favorite foods. Weight loss can occur, though this is less common in early stages. Some children experience unusual tiredness or weakness that isn’t explained by their normal activities. A low red blood cell count, called anemia, can develop and contribute to fatigue and paleness.[1][3]
Less commonly, children may experience constipation or have visible veins across their abdomen that appear larger or more prominent than normal. The tumor’s size and location can sometimes press on nearby structures, leading to these additional symptoms.[3]
Prevention
Unlike some adult cancers that can be prevented through lifestyle changes or avoiding certain exposures, nephroblastoma cannot be prevented in most cases. Because the disease develops from genetic changes that occur during fetal development or shortly after birth, there are no known behavioral modifications or environmental controls that reduce risk in the general population.[1]
However, for children at known high risk due to genetic syndromes or birth defects, a form of prevention exists through early detection screening. Regular ultrasound examinations can identify tumors when they are still small and potentially easier to treat. Healthcare providers typically recommend that high-risk children undergo abdominal ultrasound screening every three months until they reach at least age eight. Some children may need continued monitoring beyond this age depending on their specific condition.[4]
Genetic counseling offers another preventive approach for families with a history of nephroblastoma or associated genetic conditions. A genetic counselor can help families understand their risks, discuss whether genetic testing might be beneficial, and create appropriate monitoring plans for children who may be at increased risk. While this doesn’t prevent the cancer itself, it enables earlier detection and potentially more successful treatment.[4]
For children diagnosed with nephroblastoma, preventing complications and late effects of treatment becomes an important focus. Following treatment protocols carefully, attending all follow-up appointments, and maintaining overall health through good nutrition and appropriate activity levels can help minimize long-term effects and reduce the risk of cancer recurrence.[1]
Pathophysiology
Understanding how nephroblastoma develops and affects the body requires looking at both normal kidney development and what goes wrong when this cancer forms. The pathophysiology explains the physical, biochemical, and cellular changes that occur during the disease process.
Normally, kidneys develop during pregnancy from specialized embryonic tissue. This tissue, called metanephric blastema, contains immature cells that are programmed to develop into the various cell types that make up a functioning kidney. These immature cells, or nephroblasts, usually complete their transformation into mature kidney tissue before or shortly after birth. In children who develop nephroblastoma, something disrupts this normal maturation process.[2][4]
The tumor gets its name from these nephroblasts because it consists largely of cells that resemble these immature kidney cells. Instead of maturing and becoming part of normal kidney tissue, these cells continue to multiply without proper control. Genetic mutations in cells disrupt the normal signals that tell cells when to grow, when to stop growing, and when to mature into specialized tissue.[2]
At the cellular level, nephroblastoma involves several key genetic changes. The WT1 gene, located on chromosome 11, plays a critical role in normal kidney development. When this gene is altered or missing, it can no longer properly regulate cell growth and differentiation. The CTNNB1 gene is involved in a cellular signaling pathway that controls cell division and survival. Mutations here can cause cells to receive continuous growth signals even when they should stop dividing. The WTX gene, found on the X chromosome, normally helps control cell growth, and its loss removes an important brake on cell multiplication.[2]
Sometimes, a condition called nephroblastomatosis precedes tumor development. This non-cancerous condition involves the presence of multiple clusters of abnormal, immature kidney cells throughout one or both kidneys. These clusters, called nephrogenic rests, can create a thick layer around the kidney. While nephroblastomatosis itself is not cancer, these abnormal cell clusters have the potential to transform into nephroblastoma if left untreated. Children found to have nephrogenic rests in a kidney removed due to nephroblastoma face higher risk of developing tumors in their remaining kidney.[4]
As the tumor grows, it physically expands within the kidney, gradually replacing normal kidney tissue. The tumor may remain contained within a protective capsule for some time, but as it enlarges, it can break through this barrier. The cancer can spread beyond the kidney through several mechanisms. It may extend into nearby blood vessels, particularly the renal vein that drains blood from the kidney. It can infiltrate surrounding fatty tissue and structures. Cancer cells may also travel through the lymphatic system to nearby lymph nodes, small organs that help fight infection.[1][4]
When nephroblastoma spreads to distant parts of the body, a process called metastasis, the lungs are the most common destination. Liver, brain, and bones may also be affected. These metastatic tumors develop when cancer cells break away from the original tumor, enter the bloodstream or lymphatic system, and establish new growth in distant organs.[1][4]
The tumor’s impact on kidney function varies. When nephroblastoma affects only one kidney and the other kidney remains healthy, overall kidney function is usually maintained because one kidney can handle the body’s needs. However, when both kidneys are involved or if the remaining kidney after treatment doesn’t function optimally, problems with waste removal and fluid balance can develop. High blood pressure in children with nephroblastoma may result from the tumor affecting kidney structures that help regulate blood pressure, or from the tumor producing substances that affect blood vessel constriction.[1]
Under the microscope, nephroblastoma shows a characteristic appearance with three main components: blastema (the immature cells), epithelial elements (cells trying to form kidney structures), and stromal elements (supporting connective tissue). The proportions of these components vary between tumors. Some tumors show favorable histology, meaning the cells look relatively normal under the microscope. Others show unfavorable histology with severely abnormal cells called anaplastic cells. Anaplastic cells divide rapidly and respond less well to treatment, resulting in a more challenging disease course.[2]
