OVERVIEW

What are the types of kidney tumors?

Kidney tumors are mostly malignant. Clinically, the most common types are divided into three categories: renal cell carcinoma, nephroblastoma (Wilms tumor), and renal pelvic tumors, with the first being the most prevalent.

Are kidney tumors common?

Urinary system tumors account for about 2%–3% of all malignant tumors (not particularly common). Among urinary system tumors, bladder cancer is the most frequent, followed by kidney cancer. However, nephroblastoma is the most common malignant tumor in the pediatric urinary system.

Is nephroblastoma malignant? Who is most affected?

Blastomas can be either benign or malignant, but nephroblastoma is malignant. Also known as Wilms tumor or renal embryoma, it primarily occurs in children. The average age at diagnosis is 37 months for boys and 43 months for girls, with 98% of patients being under 10 years old. However, it can also occur in some adults and elderly individuals. There is no significant difference in incidence between genders or between the left and right kidneys.

SYMPTOMS

What are the clinical manifestations of Wilms tumor?

Most Wilms tumors are solitary lesions, but 5% involve both kidneys, and 7% have multiple lesions in one kidney. Wilms tumor primarily affects children, and its clinical manifestations are nonspecific. Common clinical presentations include:

• Abdominal mass: The most common symptom, often discovered accidentally by parents during bathing or dressing. The mass is usually located in the upper abdomen on the affected side and gradually enlarges. A large tumor may compress adjacent organs, causing symptoms such as shortness of breath and poor appetite.
• Abdominal pain: Varies in intensity, ranging from mild discomfort to severe colic. In younger children, it may manifest as irritability or crying.
• Hematuria: In rare cases, visible red urine may occur, possibly due to tumor invasion of the renal pelvis.
• Hypertension: Often caused by vascular compression or invasion, leading to secondary hypertension. Blood pressure usually normalizes after tumor removal.
• Other symptoms: Fever, weight loss, anemia, nausea, vomiting, cough, and loss of appetite.

What are the metastasis patterns of Wilms tumor?

The metastasis patterns of Wilms tumor are similar to those of most cancers, with three common types: hematogenous spread, lymphatic spread, and direct extension:

• Hematogenous metastasis: The most common sites are the liver and lungs, with bone marrow also frequently affected.
• Lymphatic metastasis: Tumor cells may spread via lymphatic vessels to the renal hilum and retroperitoneal lymph nodes.
• Direct invasion: If the tumor breaches the renal fascia, it may invade adjacent organs. Due to anatomical differences, the left kidney may involve the spleen, pancreas, or parts of the colon, while the right kidney may invade the liver or parts of the colon.

CAUSES

What are the causes of Wilms tumor?

Wilms tumor is mainly divided into two types:

• One is sporadic, with no clear cause, primarily occurring at around 3-5 years of age;
• The other is hereditary, related to genetics, often bilateral. If either parent has the condition, there is a 50% chance of passing it to the child, mainly occurring at around 2-5 years of age, most commonly associated with congenital aniridia.

DIAGNOSIS

What tests are needed for the diagnosis of Wilms tumor?

Urinary color Doppler ultrasound, KUB+IVP, CT, and magnetic resonance imaging (MRI). Additionally, Wilms tumor may be associated with congenital malformations. Therefore, examinations should include an evaluation of related abnormalities, such as aniridia, hemihypertrophy, and genitourinary anomalies.

What are the advantages and disadvantages of various tests for Wilms tumor?

• Urinary color Doppler ultrasound: This test is non-invasive, convenient, and can show the location, number, size, etc., of the tumor. It can also determine whether it is complicated by urinary stones or hydronephrosis. The larger the tumor, the higher the accuracy of the ultrasound. It can also detect whether the renal vein and inferior vena cava are complicated by tumor thrombi, which can guide surgical choices.
• KUB + IVP: Kidney-ureter-bladder (KUB) X-ray + intravenous pyelography (IVP). KUB has limited diagnostic value for Wilms tumor, with no obvious specificity, but it can assess the presence of urinary stones, kidney contours, and position. IVP involves injecting a contrast agent intravenously, which is excreted in the urine and visualized under an X-ray machine to display the morphology of the kidneys, ureters, and bladder. It can be used to assess the excretory function of both kidneys and the presence of masses.
• Urinary CT scan + contrast enhancement: This test is convenient and non-invasive but requires a full bladder. It can display the size of the tumor and assist in determining tumor staging.
• Magnetic resonance imaging (MRI): This test has no radiation but is relatively expensive and time-consuming. It is not suitable for individuals with magnetic implants or claustrophobia. However, its role in staging Wilms tumor is slightly greater than that of CT.

Each of the above tests has different advantages and disadvantages, and the choice should be based on hospital equipment and the patient's specific condition. Clinically, before surgery or other treatments, additional tests such as complete blood count, coagulation tests, and electrocardiogram (ECG) are needed to assess the patient's physiological status and determine surgical feasibility.

Additionally, Wilms tumor predominantly occurs in children, so cooperation during testing is essential. Sedatives may be used if necessary, and radiation exposure (e.g., KUB+IVP, CT) should minimize exposure to the child's reproductive organs.

What possible diseases should Wilms tumor be differentiated from in childhood?

In children, other kidney tumors are relatively rare, such as clear cell sarcoma of the kidney, rhabdoid tumor of the kidney, and renal cell carcinoma. These often require differentiation from Wilms tumor through postoperative histopathological examination:

• Clear cell sarcoma of the kidney: Clear cell sarcoma is the second most common pediatric kidney tumor. Its prognosis is worse than that of Wilms tumor, with higher recurrence and mortality rates. Bone is a common metastatic site, so this tumor is also known as the childhood bone-metastasizing renal tumor. Histologically, clear cell sarcoma typically presents as cords and nests of pale tumor cells, with abundant extracellular matrix separated by fine capillary arcades.
• Rhabdoid tumor of the kidney: Rhabdoid tumor of the kidney is a highly malignant renal tumor, most commonly occurring in children under 2 years old and almost never in children over 5. At diagnosis, the tumor often has already metastasized to the lungs, abdominal organs, lymph nodes, bones, and brain. The prognosis is generally poor.
• Renal cell carcinoma (RCC): Renal cell carcinoma is rare in childhood.

TREATMENT

How is Wilms tumor typically staged after diagnosis?

Countries like the United States and Canada primarily use the NWTS/COG staging system, which is based on surgical evaluation before chemotherapy. It is divided into stages I to V:

• Stage I: The tumor is confined to the kidney. It can be completely removed, with an intact renal capsule and no evidence of renal sinus vascular involvement or tumor at or beyond the surgical margin.
• Stage II: The tumor extends beyond the kidney but can be completely excised, with no evidence of tumor at or beyond the surgical margin.
• Stage III: Residual tumor remains after surgery but is confined to the abdomen. This includes regional lymph node involvement, peritoneal surface involvement, incomplete tumor resection, tumor at or beyond the surgical margin, tumor spillage, prior biopsy, or preoperative chemotherapy.
• Stage IV: Hematogenous metastasis (e.g., to the lungs, liver, bones, or brain) or lymph node involvement outside the abdominopelvic region.
• Stage V: Bilateral kidney involvement at diagnosis. Each kidney is staged separately to guide further treatment decisions.

How is Wilms tumor specifically treated?

Treatment varies depending on the stage of Wilms tumor, as follows:

• Stages I and II: After initial surgical resection, 19 weeks of chemotherapy with vincristine + dactinomycin is given, without radiotherapy. However, patients classified as very low-risk may undergo nephrectomy alone without adjuvant chemotherapy. Very low-risk criteria include age <2 years and tumor weight <550 grams.
• Stage III: After initial surgical resection, 25 weeks of triple chemotherapy (vincristine + dactinomycin + doxorubicin) is administered. Radiotherapy to the flank, hemipelvis, or whole abdomen is given based on lymph node involvement or peritoneal contamination.
• Stage IV: After initial surgical resection, 25 weeks of triple chemotherapy (vincristine + dactinomycin + doxorubicin) is given. Whole-lung irradiation is only used for patients with persistent lung metastases after 6 weeks of chemotherapy.
• Stage V: Although only 5%–7% of Wilms tumor patients have Stage V (bilateral involvement), treatment is challenging due to the need to preserve renal function while treating tumors in both kidneys. Preoperative chemotherapy (vincristine + dactinomycin + doxorubicin for 6 weeks) may be used. Postoperative chemotherapy and radiotherapy depend on histopathological findings and the presence of tumor in lymph nodes or the peritoneal cavity. Initial nephrectomy is performed on the more affected side, while partial nephrectomy or tumor excision is done on the contralateral kidney.

DIET & LIFESTYLE

What factors may be related to the prognosis of Wilms' tumor?

Wilms' tumor is primarily composed of three components: stroma (the majority), epithelium, and blastema, though some cases may consist of only one or two components.

The composition determines the prognosis. When the tumor is mainly composed of well-differentiated stroma, epithelium, or blastema (differentiation refers to the process by which primitive cells develop into specialized cells, such as cardiomyocytes; poorer differentiation indicates closer resemblance to primitive cells, while better differentiation indicates closer resemblance to specialized cells), the prognosis is favorable. Conversely, when the tumor consists of undifferentiated tissue, the prognosis is poor, though this type accounts for a relatively low proportion, approximately 4.5%.

Can Wilms' tumor be cured?

Wilms' tumor is the pediatric malignant solid tumor with the best outcomes when treated with a combination of surgery, chemotherapy, and radiation therapy. If there is no recurrence within 2–3 years after treatment, it is considered cured.

Do Wilms' tumor patients need regular follow-up examinations after treatment to achieve early detection and prevent recurrence?

Continuous monitoring is necessary. Typically, chest X-rays and abdominal ultrasounds are alternated with CT scans of the chest, abdomen, and pelvis. During treatment, imaging examinations are performed every 6–8 weeks; then every 3 months for 2 years; followed by every 6 months for another 2 years. Additionally, some patients may require more frequent abdominal ultrasounds.

PREVENTION

Can Wilms Tumor Be Prevented?

The cause of Wilms tumor is unknown, and there are no specific preventive measures. It is recommended to seek medical attention promptly if abnormalities are detected and to receive treatment as early as possible.