Causes and Underlying Mechanisms
Wilms tumor occurs when immature kidney cells do not develop as expected and instead form a mass. The exact cause of this error is often unknown, but it involves changes (mutations) in the DNA of kidney cells. In a small number of cases, these genetic changes are inherited from a parent, but most occur by chance during the child's early development. Specific genes such as WT1 and WT2 have been linked to the condition.

Risk Factors
While most children who develop Wilms tumor have no known risk factors, certain groups are more likely to be affected. Risk factors include:

• Age: It is most common in children aged 3 to 4.
• Race: Black children have a slightly higher risk compared to children of other races.
• Family History: Having a family member with the condition slightly increases risk, though this is rare.
• Genetic Syndromes: Certain birth defect syndromes, such as Beckwith-Wiedemann syndrome, WAGR syndrome, and Denys-Drash syndrome, are strongly linked to Wilms tumor.

Prevention
There are currently no known lifestyle changes or environmental strategies to prevent Wilms tumor, as it is largely driven by genetic factors. For children with known high-risk genetic syndromes, doctors recommend regular screening with abdominal ultrasounds. This does not prevent the tumor from forming, but it helps catch the disease at an early, more treatable stage.

Signs and Symptoms
The most common sign of Wilms tumor is a firm, smooth lump or swelling in the abdomen that is usually painless. Parents often notice this mass while bathing or dressing the child. Because the tumor can grow quite large before being discovered, the belly may look uneven or distended. Other symptoms can include:

• Blood in the urine (hematuria), which may make urine look pink or red
• Fever that cannot be explained by an infection
• High blood pressure, which might cause headaches
• Abdominal pain or discomfort
• Loss of appetite and nausea
• Constipation

Diagnosis and Identification
Doctors typically start with a physical exam to feel for a mass in the abdomen. If a tumor is suspected, imaging tests are used to confirm the diagnosis and check for spread. Common tests include:

• Ultrasound: Uses sound waves to create images of the kidney and is often the first test used.
• CT Scan or MRI: Provides detailed cross-sectional images to determine the size of the tumor and whether it has spread to nearby lymph nodes or the other kidney.
• Chest X-ray or CT: Checks if the cancer has spread to the lungs.
• Blood and Urine Tests: Evaluate kidney function and overall health, though they do not diagnose the tumor directly.

Differential Diagnosis
Clinicians must distinguish Wilms tumor from other causes of abdominal masses in children. It is most often confused with neuroblastoma, another childhood cancer that can occur in the abdomen. The specific location of the tumor and how it appears on imaging helps doctors tell the difference.

Treatment Options
The primary treatment for Wilms tumor involves a combination of surgery and chemotherapy, and sometimes radiation therapy. The specific plan depends on the stage of the cancer and the appearance of the cells under a microscope (histology). Treatment is generally very effective.

• Surgery: The most common first step is a procedure called a radical nephrectomy, where the entire affected kidney is removed. In rare cases where both kidneys are affected, surgeons may remove just the tumor (partial nephrectomy) to save kidney function.
• Chemotherapy: Powerful medications are used to kill cancer cells. This is often given after surgery to destroy any remaining cells, but in some cases, it may be used before surgery to shrink the tumor. Common drugs include vincristine and dactinomycin.
• Radiation Therapy: High-energy beams may be used for more advanced stages or aggressive tumor types to kill cancer cells that have spread.

Management and Monitoring
During treatment, children require close monitoring for side effects such as infection, fatigue, and nausea. Long-term follow-up is essential to check for recurrence and to monitor the health of the remaining kidney and the heart, as some treatments can have late effects.

When to Seek Medical Care
Parents should contact a healthcare provider if they notice any unusual swelling or lumps in their child's belly. After diagnosis, seek immediate care if the child experiences:

• A fever of 100.4°F (38°C) or higher during chemotherapy
• Signs of infection around a surgical incision (redness, pus, or warmth)
• Uncontrolled vomiting or inability to drink fluids
• Sudden, severe abdominal pain

Severity and Staging
Wilms tumor is a serious condition but is one of the most curable childhood cancers. Severity is determined by the stage of the disease (I through V) and the histology (how the cells look).

• Stage I: The tumor is contained within one kidney and can be completely removed with surgery.
• Stage II: The cancer has spread beyond the kidney but is still completely removed by surgery.
• Stage III: Cancer remains in the abdomen after surgery or has spread to lymph nodes.
• Stage IV: Cancer has spread to distant parts of the body, such as the lungs or liver.
• Stage V: Tumors are found in both kidneys at the time of diagnosis (bilateral).

Prognosis and Outlook
The prognosis for Wilms tumor is generally excellent. Children with "favorable histology" (cells that look less abnormal) have a survival rate of over 90%. Even children with more advanced stages often respond well to treatment. However, a small percentage of tumors have "anaplastic histology" (more aggressive cells), which can be harder to treat and carries a higher risk of recurrence.

Long-Term Effects
Most children go on to live normal, healthy lives. However, survivors are at risk for certain long-term complications due to the cancer or its treatment. These can include:

• Decreased kidney function (usually managed well with the remaining kidney)
• Heart problems related to certain chemotherapy drugs
• fertility issues (rare, but possible depending on treatment)
• Secondary cancers later in life

Impact on Daily Activities
During treatment, a child's daily routine will change significantly due to surgery recovery and chemotherapy schedules. They may need to miss school and avoid crowded places to reduce the risk of infection. Fatigue and nausea can affect their energy levels for play and activities. Once treatment is complete, most children return to their normal activities. Children with one kidney can typically play sports and live normally, though some doctors may advise avoiding high-impact contact sports to protect the remaining kidney.

Emotional and Social Support
A cancer diagnosis is stressful for the entire family. Children may feel anxious about medical procedures or changes in their appearance, such as hair loss. Siblings may also feel confused or neglected. Connecting with support groups, social workers, or counselors can help families cope with the emotional challenges.

Questions to Ask Your Healthcare Provider
Asking the right questions can help you understand the diagnosis and treatment plan. Consider asking:

• What is the stage and histology of the tumor?
• Will my child need radiation in addition to surgery and chemotherapy?
• How will this treatment affect my child's future growth and development?
• What are the signs of infection I should watch for during chemotherapy?
• How often will my child need check-ups after treatment ends?
• Are there any specific activities or foods my child should avoid?
• What resources are available for school support and financial assistance?

Q: Is Wilms tumor hereditary?
A: In most cases, Wilms tumor is not hereditary and occurs sporadically. Only about 1% to 2% of cases are passed down in families. However, children with certain genetic syndromes are at higher risk.

Q: Can a child live a normal life with one kidney?
A: Yes, the body can function very well with a single healthy kidney. The remaining kidney typically grows larger and takes over the work of the removed one. No special diet is usually needed, but hydration is important.

Q: How long does treatment typically last?
A: The duration depends on the stage of the cancer. Treatment usually lasts between 6 months to a year, involving surgery followed by rounds of chemotherapy and potentially radiation.

Q: What is the survival rate for Wilms tumor?
A: The overall survival rate is approximately 90%. For early-stage tumors with favorable cell types, the survival rate is even higher, making it one of the most curable childhood cancers.

Q: Can Wilms tumor come back after treatment?
A: Recurrence is possible, usually within the first two years after treatment. Regular follow-up scans are crucial to catch any return of the disease early, when it can still be treated effectively.