Nephroblastoma, also known as Wilms tumor or nephroembryoma, is the most common malignant renal tumor in children. It accounts for approximately 95% of pediatric renal tumors and 6%–7% of all childhood malignancies.
Pathology
Nephroblastoma is often encapsulated with a pseudocapsule, displaying a homogeneous gray-white cut surface, frequently accompanied by hemorrhage and necrosis with occasional cystic cavity formation. After breaching the renal capsule, the tumor may invade surrounding tissues and organs extensively. Lymphatic metastasis can occur, often involving the renal hilum and periaortic lymph nodes. Nephroblastoma originates from embryonic renal tissue and is characterized histologically by a malignant mixed composition of blastemal, epithelial, and stromal elements. On the molecular level, common genetic abnormalities include WT1 gene mutations, WTX gene deletions, and alterations at the 11p15 chromosomal locus. Hematogenous metastasis most often affects the lungs, followed by the liver, brain, and other organs.
Clinical Manifestations
More than 80% of cases occur before the age of five, with a mean age of 3.5 years. Gender incidence is approximately equal, and bilateral cases account for about 5%. An asymptomatic abdominal mass, observed in over 90% of cases, is the most common and significant presenting feature, often discovered incidentally by parents or physicians. The mass is typically located in the upper abdomen near the flank, with a smooth surface, moderate firmness, no tenderness, and some degree of mobility. In some cases, the tumor is large enough to cross the midline and may become relatively fixed. Approximately 20% of patients present with hematuria, and around 25% have hypertension at the time of diagnosis. Other common symptoms include fever, anorexia, and weight loss. Tumor rupture and hemorrhage can occasionally present as an acute abdomen. In advanced stages, symptoms such as nausea, vomiting, and anemia may occur. Additionally, some children may present with associated abnormalities such as aniridia, genitourinary malformations, or hemihypertrophy.
Diagnosis and Differential Diagnosis
The possibility of nephroblastoma should be considered when an upper abdominal mass is identified in a child. Imaging studies have decisive value in making the diagnosis. Ultrasound aids in determining the nature of the mass as solid. CT and MRI provide detailed information on tumor extent as well as the involvement of adjacent lymph nodes, organs, renal veins, and the inferior vena cava. Chest X-rays and CT scans are crucial for assessing pulmonary metastasis.
Nephroblastoma must be differentiated from conditions such as giant hydronephrosis and adrenal neuroblastoma. Giant hydronephrosis presents as a soft, cystic mass, and ultrasound can easily distinguish it from tumors. Adrenal neuroblastoma may invade the kidney directly, often appearing nodular and located closer to the midline. Measuring catecholamine metabolites, such as vanillylmandelic acid (VMA) and homovanillic acid (HVA), can assist in diagnosing neuroblastoma.
Treatment and Prognosis
A multidisciplinary approach involving surgery, chemotherapy, and radiotherapy significantly improves postoperative survival rates. Abdominal radical nephrectomy serves as the initial treatment for most patients. Surgery not only achieves complete tumor resection but also facilitates more accurate tumor staging, providing a basis for subsequent chemotherapy and radiotherapy. For patients in whom partial nephrectomy is planned, those where complete resection is not feasible in a single session, or those with tumor thrombi extending above the hepatic vein, preoperative neoadjuvant chemotherapy is recommended. Actinomycin D (AMD) and vincristine (VCR) are the first-line chemotherapeutic agents, with better efficacy observed when used in combination. Preoperative radiotherapy is indicated for large nephroblastomas with insufficient tumor shrinkage after chemotherapy. Postoperative radiotherapy should be initiated within 10 days; delays increase the risk of local tumor recurrence.
With the adoption of comprehensive treatment strategies, the five-year survival rate for nephroblastoma has improved significantly to over 90%. For bilateral nephroblastoma, auxiliary therapy is administered before bilateral tumor resection. Renal function in the contralateral kidney must be confirmed before performing nephrectomy for unilateral nephroblastoma.
Nephroblastoma in adults has a much poorer prognosis and requires early diagnosis and aggressive surgical treatment. Postoperative therapies, including radiotherapy and chemotherapy guided by pathological classification and staging, can significantly enhance cure rates and improve outcomes.