Recommended Staging System for Wilms Tumor
The recommended staging system for Wilms tumor is the National Wilms Tumor Study Group (NWTSG) staging system, which classifies tumors into stages I through V based on surgical findings and tumor extent. 1
NWTSG Staging System Overview
Stage I: Tumor limited to kidney and completely excised; renal capsule intact; no tumor rupture or biopsy prior to removal; no residual tumor apparent beyond margins of resection 2
Stage II: Tumor extends beyond kidney but is completely removed; regional extension of tumor (penetration of renal capsule or extensive invasion of renal sinus); vessels outside kidney contain tumor thrombus; biopsy or local spillage confined to flank 3
Stage III: Residual non-hematogenous tumor confined to abdomen; any of the following: lymph node involvement; diffuse peritoneal contamination by tumor spillage; peritoneal implants; tumor beyond surgical margins either microscopically or grossly; tumor not completely removed 3, 4
Stage IV: Hematogenous metastases or lymph node metastases outside the abdomen (lung, liver, bone, brain) 4
Stage V: Bilateral renal involvement at diagnosis (each side should be staged separately) 2, 5
Clinical Significance of Staging
Accurate staging is critical as it directly impacts treatment decisions and survival outcomes 5
Stage I-II favorable histology tumors have excellent outcomes with 4-year overall survival of 98.3% and 92% respectively 2, 3
Stage III favorable histology has 4-year event-free survival of 88% and overall survival of 97% with appropriate therapy 3
Stage IV disease has significantly lower survival rates, with 4-year event-free survival around 33.3% for anaplastic histology 2
Bilateral disease (Stage V) has 4-year event-free survival of approximately 43.8% and overall survival of 55.2% 2
Prognostic Factors Beyond Staging
Histology: Favorable histology vs. anaplastic histology (diffuse or focal) is a critical determinant of prognosis 2
Genetic markers: Loss of heterozygosity (LOH) at chromosomes 1p and 16q is associated with poorer outcomes in all stages 3
Lymph node status: Negative lymph node status is associated with better event-free survival 3
Age at diagnosis: Adults with Wilms tumor have different outcomes compared to children, with 5-year disease-specific survival of 95.7% 4
Special Considerations in Staging
Genetic testing for predisposition syndromes (TRIM28, REST, CTR9, DIS3L2) should be considered as part of comprehensive evaluation 6
Patients with epithelial-predominant histology should be tested for TRIM28 pathogenic variants, as 86% of these tumors harbor TRIM28 variants 6
Bilateral tumors require careful consideration, as they often represent genetic predisposition syndromes requiring surveillance of family members 6
For patients with delayed nephrectomy after preoperative chemotherapy, histologic response in the nephrectomy specimen provides additional prognostic information 3
Surveillance Recommendations Based on Staging
For patients with identified genetic predisposition syndromes, renal ultrasound surveillance every 3 months until 8 years of age is recommended 6
For patients with stage I-IV disease who have completed therapy, continued surveillance is recommended, especially for those with genetic predisposition syndromes 6
The risk of second tumors after completion of therapy may be higher in patients with genetic predisposition syndromes compared to the general population 6
Surveillance should be tailored based on specific genetic findings, with special attention to those with REST, CTR9, and TRIM28 pathogenic variants 6