Wilms Tumor

Because of the relative rarity of this tumor, all patients with Wilms tumor should be considered for entry into a clinical trial. Treatment planning by a multidisciplinary team of cancer specialists (pediatric surgeon or pediatric urologist, pediatric radiation oncologist, and pediatric oncologist) with experience treating Wilms tumor is required to determine and implement optimum treatment.

The National Wilms Tumor Study (NWTS) Group, which is now part of the Children's Oncology Group, has established standard treatment for Wilms tumor in North America which consists of surgery followed by chemotherapy and, in some patients, radiation therapy.[1,2,3] The major treatment conclusions of the National Wilms Tumor Studies (NWTS 1-5) are as follows:

1. Routine, postoperative radiation therapy of the flank is not necessary for children with stage I tumors or stage II tumors with favorable histology (FH) when postnephrectomy combination chemotherapy consisting of vincristine and dactinomycin is administered.
2. The prognosis for patients with stage III FH is best when treatment includes: (a) dactinomycin, vincristine, doxorubicin, and 10.8 Gy of radiation therapy to the flank; or (b) dactinomycin, vincristine, and 20 Gy of radiation therapy to the flank.
3. The addition of cyclophosphamide to the combination of vincristine, dactinomycin, and doxorubicin does not improve prognosis for patients with stage IV FH tumors.
4. A single-dose of dactinomycin per course (stages I-II FH, stage I anaplastic, stage III FH, stages III-IV, or stages I-IV clear cell sarcoma of the kidney) is equivalent to the divided-dose courses, and results in the same event-free survival, greater dose intensity, and is associated with less toxicity and expense.[4]
5. Eighteen weeks of therapy is adequate for patients with stage I FH whereas other patients can be treated with 6 months of therapy instead of 15 months.[1,4,5,6,7]
6. Tumor-specific loss of heterozygosity for combined 1p and 16q predicts recurrence of FH Wilms tumor and may be used to select patients for more aggressive treatment.[8]

Operative principles have evolved from NWTS trials. The most important role for the surgeon is to ensure complete tumor removal without rupture and perform an assessment of the extent of disease. Radical nephrectomy and lymph node sampling via a transabdominal incision is the procedure of choice.[9] For patients with resectable tumors, preoperative biopsy should not be performed.[9] Routine exploration of the contralateral kidney is not necessary if technically adequate imaging studies do not suggest a bilateral process. If the initial imaging studies are suggestive of regional and contralateral kidney involvement, the contralateral kidney should be formally explored to rule out bilateral involvement. This should be done prior to nephrectomy since the diagnosis of bilateral disease would dramatically alter the approach.[10] Partial nephrectomy remains controversial and is not recommended except for bilateral tumors. Also, some rare, very small tumors may be discovered by ultrasound screening, and these cases may be considered for partial nephrectomy.[11] In North America, renal-sparing partial nephrectomy of unilateral Wilms tumor following administration of chemotherapy to shrink the tumor mass is considered investigational.[12,13] Hilar, periaortic, iliac, and celiac lymph node sampling is mandatory.[9] Furthermore, any suspicious node basin should be sampled. Margins of resection, residual tumor, and any suspicious node basins should be marked with titanium clips. Liver wedge resection or partial duodenal or colonic resections are acceptable for complete en bloc excision. Wilms tumor arising in a horseshoe kidney is rare and accurate preoperative diagnosis is important in planning the operative approach. Primary resection is possible in most cases. Inoperable cases can usually be resected after chemotherapy.[14]