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Wilm's Tumor. (4 marks) (GMC)*** *Wilm's tumors. (2 marks) (NAMO)

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I now have all the information needed for a comprehensive, exam-ready answer. Here is the full write-up:

Wilms' Tumor (Nephroblastoma)

Definition

Wilms' tumor (nephroblastoma) is the most common primary malignant renal tumor of childhood and the fourth most common pediatric malignancy overall. It is an embryonal tumor that develops from remnants of immature metanephric kidney tissue.

Epidemiology

  • Incidence: ~1 in 10,000 children
  • Peak age: 2-5 years (95% of cases before age 10)
  • 5-10% are bilateral (synchronous or metachronous)
  • Bilateral tumors present ~10 months earlier - suggesting a germline mutation
  • ~500 new cases/year in the US
  • Overall cure rate: ~90% (one of the great successes of pediatric oncology, up from ~30% decades ago)

Pathogenesis and Genetics

Associated Syndromes (10% of cases - but key to understanding)

SyndromeFeaturesGene/LocusWilms' Risk
WAGR syndromeWilms' tumor, Aniridia, Genital anomalies, mental RetardationWT1 deletion + PAX6 deletion at 11p13~33%
Denys-Drash syndrome (DDS)Gonadal dysgenesis (male pseudohermaphroditism), diffuse mesangial sclerosis, early renal failureDominant-negative missense mutation in WT1 (zinc-finger region), 11p13~90%
Beckwith-Wiedemann syndrome (BWS)Visceromegaly, macroglossia, hemihypertrophy, hyperinsulinemic hypoglycemiaWT2 locus (11p15.5) - loss of imprinting of IGF2 gene; paternal allele overexpressedIncreased
WAGR and DDS involve WT1 inactivation (two-hit mechanism for tumorigenesis). BWS involves IGF2 overexpression due to loss of imprinting - also predisposes to hepatoblastoma, adrenocortical tumors, rhabdomyosarcoma, and pancreatic tumors.

Sporadic (90%) Molecular Alterations

  • ~10%: gain-of-function mutations in β-catenin
  • 15-20%: mutations in genes encoding microRNA processing proteins, reducing levels of mature miRNAs involved in mesenchymal-to-epithelial transformation - leading to persistent blastemal rests
  • TP53 mutations: associated with anaplastic histology and poor prognosis

Morphology

Gross Pathology

  • Typically large, solitary, well-circumscribed mass replacing renal parenchyma
  • 10% are bilateral or multicentric
  • Cut surface: soft, homogeneous, tan-to-gray, with occasional hemorrhage, cystic degeneration, and necrosis
Wilms tumor gross specimen - large, well-circumscribed tan-to-gray mass in the lower pole of the kidney
Gross specimen: Wilms' tumor occupying the lower pole of the kidney, showing the characteristic tan-to-gray color and well-circumscribed margins. - Robbins & Kumar Basic Pathology

Histology - Classic TRIPHASIC Pattern

The hallmark is recapitulation of different stages of nephrogenesis:
  1. Blastemal component - sheets of small, round, blue cells with scant cytoplasm (resembling embryonic metanephric blastema)
  2. Epithelial component - abortive tubules or primitive glomeruli
  3. Stromal component - fibroblastic or myxoid cells; skeletal muscle differentiation is not uncommon
Histology of Wilms' tumor: (A) Triphasic pattern showing blastemal blue cells and epithelial tubules; (B) Focal anaplasia with hyperchromatic pleomorphic nuclei and abnormal mitosis
Fig A: Classic triphasic Wilms' tumor - tightly packed blue blastemal cells with interspersed primitive tubules (arrows). Fig B: Focal anaplasia - hyperchromatic pleomorphic nuclei and abnormal mitosis (center). - Robbins & Kumar Basic Pathology

Anaplasia (~5% of tumors)

  • Cells with large, hyperchromatic, pleomorphic nuclei and abnormal mitoses
  • Correlates with acquired TP53 mutations
  • Associated with chemotherapy resistance and adverse prognosis
  • Diffuse anaplasia = indicator of unfavorable histology

Nephrogenic Rests

  • Precursor lesions of Wilms' tumor (putative)
  • Present in renal parenchyma adjacent to the tumor
  • Contain immature tubules, glomeruli, and cells resembling Wilms' tumor
  • Their presence mandates close surveillance of the contralateral kidney

Clinical Features

  • Asymptomatic abdominal/flank mass - most common presentation; often discovered by parent while bathing/dressing the child
  • Hypertension
  • Hematuria
  • Abdominal pain, fever
  • Intestinal obstruction (from tumor pressure)
  • Occasionally discovered after blunt abdominal trauma

Staging (NWTSG)

StageDescription
Stage ITumor limited to kidney, completely excised
Stage IIExtends beyond kidney but completely excised (capsule penetration, renal sinus involvement)
Stage IIIResidual non-hematogenous tumor in abdomen (positive nodes, peritoneal contamination, incomplete excision)
Stage IVHematogenous metastases (lung, liver, bone, brain)
Stage VBilateral renal involvement at diagnosis

Investigations

  • Abdominal + chest CT scan - characterizes the mass, detects metastases, evaluates the contralateral kidney, identifies nephrogenic rests
  • Abdominal ultrasound - evaluates renal vein or inferior vena cava extension
  • Urine catecholamines - to exclude neuroblastoma

Treatment

Surgery

  • Radical nephroureterectomy with transperitoneal approach through a large transverse incision
  • Early control of the renal pedicle (to prevent hematogenous spread)
  • Sampling of regional lymph nodes mandatory
  • Tumor rupture must be avoided (upstages to Stage III)
  • Bilateral disease: biopsy both lesions → preoperative chemo → nephron-sparing surgery

Chemotherapy

  • Actinomycin D + Vincristine (favourable histology, early stages)
  • Adding Doxorubicin for higher stages
  • Radiation for Stage III/IV or unfavorable histology

Two Major Study Group Approaches

  • NWTSG (North America): Surgery first, then chemo ± radiation
  • SIOP (Europe): Preoperative chemotherapy to shrink tumor first, then surgery
  • Both groups agree on preoperative chemo for: bilateral disease, IVC involvement above hepatic veins, or solitary kidney involvement

Prognosis

  • Stage I/II with favorable histology: ~97% 4-year survival
  • Overall survival: ~90%
  • Unfavorable histology (diffuse anaplasia, blastemal predominance): significantly worse
  • Diffuse anaplasia is the most important adverse prognostic factor

Key Summary (for 2-mark questions)

  • Definition: Most common primary renal tumor of childhood; embryonal tumor (nephroblastoma); peak age 2-5 years
  • Associated syndromes: WAGR (WT1 deletion, 11p13), Denys-Drash (WT1 mutation, 90% risk), Beckwith-Wiedemann (IGF2 imprinting, 11p15)
  • Histology: Classic triphasic pattern - blastemal + epithelial + stromal; anaplasia = poor prognosis
  • Presentation: Asymptomatic flank mass in a young child
  • Treatment: Nephrectomy + chemotherapy ± radiotherapy; ~90% cure rate
Sources: Robbins & Kumar Basic Pathology; Robbins, Cotran & Kumar Pathologic Basis of Disease; Schwartz's Principles of Surgery 11e; Campbell-Walsh-Wein Urology

Wilm's Tumor. (4 marks) (GMC)*** *Wilm's tumors. (2 marks) (NAMO

I already covered this topic in full detail in the previous response. Here is a clean, exam-focused version formatted for both the 4-mark (GMC) and 2-mark (NAMO) weightings:

Wilms' Tumor (Nephroblastoma)

For 2-mark answer (NAMO)

Definition: Wilms' tumor (nephroblastoma) is the most common primary malignant renal tumor of childhood, arising from remnants of immature metanephric kidney (embryonal tumor). Peak age: 2-5 years. Presents as a large, asymptomatic abdominal mass in a young child. Histologically shows a classic triphasic pattern - blastemal + epithelial + stromal cells. Treatment: nephrectomy + chemotherapy. Overall cure rate ~90%.

For 4-mark answer (GMC)

Definition & Epidemiology

  • Most common primary renal tumor of childhood; 4th most common pediatric malignancy
  • Incidence: ~1 in 10,000 children; peak age 2-5 years
  • 5-10% bilateral (synchronous or metachronous)
  • Cure rate: ~90% (up from 30% decades ago)

Associated Syndromes & Genetics

SyndromeFeaturesGeneRisk
WAGRWilms', Aniridia, Genital anomalies, mental RetardationWT1 deletion + PAX6, 11p13~33%
Denys-Drash (DDS)Gonadal dysgenesis, diffuse mesangial sclerosis, early renal failureWT1 dominant-negative mutation, 11p13~90%
Beckwith-WiedemannVisceromegaly, macroglossia, hemihypertrophyLoss of imprinting of IGF2, 11p15.5Increased
  • 90% of cases are sporadic - β-catenin gain-of-function (~10%), miRNA processing mutations (15-20%)
  • TP53 mutations → anaplastic histology → worst prognosis

Morphology

Gross:
  • Large, solitary, well-circumscribed mass
  • Soft, tan-to-gray on cut section; with hemorrhage and necrosis
Wilms tumor gross - tan-to-gray well-circumscribed mass in lower pole of kidney
Microscopy - Classic Triphasic Pattern:
  1. Blastemal - sheets of small round blue cells (resembles embryonic metanephric blastema)
  2. Epithelial - abortive tubules or primitive glomeruli
  3. Stromal - fibroblastic/myxoid cells; skeletal muscle differentiation may occur
Histology: (A) triphasic Wilms' tumor - blastemal cells with epithelial tubules (arrows); (B) anaplasia with hyperchromatic pleomorphic nuclei and abnormal mitosis
Anaplasia (~5%):
  • Large hyperchromatic pleomorphic nuclei + abnormal mitoses
  • Linked to TP53 mutations; indicates chemotherapy resistance and poor prognosis
Nephrogenic rests:
  • Putative precursor lesions of Wilms' tumor
  • Presence warrants surveillance of the contralateral kidney

Clinical Features

  • Asymptomatic flank/abdominal mass - most common (often found by parent while bathing child)
  • Hypertension, hematuria, abdominal pain, fever
  • Occasionally after blunt abdominal trauma

Staging (NWTSG)

StageDescription
IConfined to kidney, completely excised
IIBeyond kidney but completely excised
IIIResidual abdominal tumor (nodes, spillage, incomplete excision)
IVHematogenous metastases (lung, liver)
VBilateral renal involvement

Treatment

ComponentDetails
SurgeryRadical nephroureterectomy; transperitoneal approach; early renal pedicle control; lymph node sampling
ChemotherapyActinomycin D + Vincristine (± Doxorubicin for higher stages)
RadiotherapyStage III/IV or unfavorable histology
Bilateral diseaseBiopsy → chemo → nephron-sparing surgery
  • NWTSG approach: surgery first, then chemo
  • SIOP (European) approach: preoperative chemo to shrink tumor, then surgery
  • Both agree on preoperative chemo for bilateral disease, IVC involvement above hepatic veins, or solitary kidney

Prognosis

  • Stage I/II, favorable histology: ~97% 4-year survival
  • Overall: ~90% survival
  • Diffuse anaplasia = most important adverse prognostic indicator
Sources: Robbins & Kumar Basic Pathology; Robbins, Cotran & Kumar Pathologic Basis of Disease; Schwartz's Principles of Surgery 11e; Campbell-Walsh-Wein Urology
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