Wilms’ Tumor

NATURAL HISTORY

Wilms’tumor is often localized at diagnosis. It is curable in most children.
Spread may occur throughout the peritoneal cavity, especially if there has been preoperative rupture or the disease has been spilled at surgery. However, the results of the Second National
Wilms’ Tumor Study (NWTS-2) demonstrated that tumor spillage at surgery, when localized to the flank, is less important prognostically than formerly believed (6, 11).
The lungs are the most common metastatic site, followed by the liver. In NWTS-2, 57 patients (11.4%) had metastases at diagnosis; 47 of these had pulmonary metastases only (6).

PROGNOSTIC FACTORS

Poor prognosis is seen in patients with extensive tumors, diploid tumors, unfavorable (anaplastic) histology, and chromosomal loss in 1p and 16q (15).
NWTS-2 showed the importance of lymph node involvement as a prognostic factor.

CLINICAL PRESENTATION

The classic presentation for Wilms’tumor is that of a healthy child in whom abdominal swelling is discovered by the child’s mother, pediatrician, or family practitioner during a routine physical examination.
A smooth, firm, nontender mass on one side of the abdomen is felt (17).
Gross hematuria occurs in as many as 25% of these cases.
The child may be hypertensive or have nonspecific symptoms, such as malaise or fever.
Only rarely does a patient present with symptomatic metastases.

DIAGNOSTIC WORKUP

Plain films of the abdomen may demonstrate calcifications, which occur in 60% to 70% of neuroblastomas and 15% of Wilms’tumors.
An excretory urogram (intravenous pyelogram) can differentiate renal tumor from other conditions. Cysts often appear as radiolucent areas.
Ultrasonography may be helpful because, in up to 10% of Wilms’tumor patients, the kidney cannot be seen on intravenous pyelogram.
Abdominal computed tomography (CT) delineates the intrarenal tumor and demonstrates gross extrarenal spread, lymph node involvement, liver metastases, and the status of the opposite kidney.

TABLE 46-1 Pretreatment Workup for Patients with Renal Mass Suspected of Wilms’ Tumor According to National Wilms’ Tumor Study No. 5 Recommendations

History	Record preexisting conditions, family history of cancer, or congenital defects
Physical examination	Blood pressure, weight, height, presence of abdominal masses, congenital anomalies, particularly genitourinary, hemihypertrophy, and aniridia
Laboratory	Hemoglobin, white cell and differential counts, platelets, urinalysis, serum blood urea nitrogen, creatinine, alanine and aspartate aminotransferases, alkaline phosphatase
Radiology	Posteroanterior and lateral chest films, excretory urogram (intravenous pyelography), computed tomography scan of the abdomen, abdominal ultrasonography, x-ray skeletal survey, and radionuclide bone scan for patients with clear-cell sarcoma
	Magnetic resonance imaging scan of the brain in clear-cell sarcoma and rhabdoid tumor of the kidney
	Bone marrow aspiration and biopsy with clear-cell sarcoma
Source: From Kalapurakal JA, Thomas PRM. Wilms’ tumor. In: Halperin, EC, Perez CA, Brady LW, eds. Principles and practice of radiation oncology, 5th ed. Philadelphia, PA: Lippincott Williams & Wilkins, 2008:1850-1858, with permission.

A direct comparison of CT with ultrasonography suggests that CT is a better diagnostic tool overall.
Clinical and imaging impression does not obviate the need for inspection at laparotomy.
Plain chest radiography is essential. Chest CT may reveal some early lesions not visible on routine radiography, but it adds little when the chest radiographs are clearly positive.
A detailed discussion of the issues in diagnostic imaging has been published (1).
A complete blood count and urinalysis should be performed. Serum blood urea nitrogen and creatinine levels and liver function tests are routine.
If neuroblastoma is not ruled out, a test for urinary catecholamines should be performed.
Table 46-1 outlines the pretreatment investigations recommended in the NWTS-5.

STAGING

Tumor staging is performed by carefully examining the operative and the histopathologic findings.
The most widely used staging system was devised by the NWTS (Table 46-2) (11), after analysis of NWTS-1 and NWTS-2 results, in which a grouping system had been used.

PATHOLOGIC CLASSIFICATION

Prognosis is affected by which of the many variants of Wilms’tumor is present (21).
Although histopathologists had attempted to relate appearance to prognosis, no generally acceptable classification was available until the report of Beckwith and Palmer (3) from the NWTS-1.

TABLE 46-2 National Wilms’ Tumor Study Staging System

*Stage*		*Description*
I		Tumor limited to kidney and completely excised; surface of renal capsule intact; tumor not ruptured before or during removal; no residual tumor apparent beyond margins of resection.
II		Tumor extends beyond kidney but is completely excised; regional extension of tumor (i.e., penetration through outer surface of renal capsule into perirenal soft tissues); vessels outside kidney substances infiltrated or contain tumor thrombus. Tumor may have been examined on biopsy, or there has been local spillage of tumor confined to flank. No residual tumor apparent at or beyond margins of excision.
III		Residual nonhematogenous tumor confined to abdomen. Any of the following may occur:
	A	Lymph nodes on biopsy found to be involved in hilus, periaortic chains, or beyond.
	B	Diffuse peritoneal contamination by tumor such as spillage of tumor beyond flank before or during surgery or by tumor growth that has penetrated through peritoneal surface.
	C	Implants found on peritoneal surfaces.
	D	Tumor extends beyond surgical margins either microscopically or grossly.
	E	Tumor not completely excisable because of local infiltration into vital structures.
IV		Hematogenous metastases; deposits beyond stage III (e.g., lung, liver, bone, brain).
V		Bilateral renal involvement at diagnosis; attempt should be made to stage each side according to the above criteria on the basis of extent of disease before biopsy.
Source: From Farewell VT, D’Angio GJ, Breslow N, et al. Retrospective validation of a new staging system for Wilms’ tumor. Cancer Clin Trials 1981;4:167, with permission.

The NWTS classifies all tumors as having favorable histology (FH) or unfavorable histology (UH) for purposes of treatment. Of 1,465 randomized patients on NWTS-3,163 (11.1%) had UH histology (5).
Renal cell carcinomas and congenital neuroblastic nephromas are not considered Wilms’ tumor.
Two monoplastic sarcomatous varieties are no longer considered true Wilms’tumors, but have been included in NWTS protocols (2).

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