Epidemiology
Most common primary renal tumour in children – an embryonal tumour which develops from remnants of immature kidney.
6 – 7 % of childhood cancers.
> 90 % of renal tumours in children.
Peak age of presentation is 3 – 4 years of age.
50 % higher prevalence in Afro-Caribbean children.
90 % are sporadic – remaining associated with syndromes (Denys-Drash, WAGR, Beckwith-Wiedemann). Those presenting with bilateral tumours, or associated with syndromes, are generally younger.
Pathology
Majority arise from somatic mutations – many different genes have been implicated eg. WT1, WTX, IGF2 in different proportion of cases.
Wide histologic variety.
Classic Wilms tumour described as triphasic / three types of cells – islands of compact undifferentiated blastema, epithelial cells, and stromal component.
More than a third of kidneys resected for Wilms have nephrogenic rests. These have a varied natural history – most do not go on to form Wilms tumour and they have been found in 1 % of post-mortem infants.
Main prognostic factor is the presence of anaplasia which signifies more aggressive disease.
Presentation
Usually palpable asymptomatic mass felt by parents.
Haematuria, abdominal pain or hypertension are other presentations. Minor trauma causing bleed/pain has been well described.
Can be picked up on 3 monthly screening ultrasounds for those at high risk (Denys-Drash, WAGR, Beckwith-Wiedemann etc). Aniridia (no iris of eye) is associated.
Differential diagnosis
Mesoblastic nephroma – usually < 1 year of age, benign large masses
Cystic nephroma
AML
Clear cell sarcoma – 2 – 3 years – present similar to Wilms, metastasise early
Malignant rhabdoid tumour
Neuroblastoma
RCC (typically > 12 yrs old)
XGP
Investigations and work-up
Abdominal ultrasound – including renal vein and cava
4 – 10 % may have renal vein / caval thrombus
CT or MRI +/- chest
Bloods – including coags which may be altered.
Urinalysis – proteinuria may need investigation for Denys-Drash etc, urine VMA levels for neuroblastoma
Management
Protocol driven, but two different protocols with different philosophies and similar outcomes.
Principles of nephrectomy for Wilms tumour:
- Usually an open, transperitoneal nephrectomy with lymph node sampling, through a transverse incision
- Adrenal gland may or may not be taken
- Perihilar and paracaval/para-aortic nodes should be sampled
- Complete exploration of the abdomen – palpate liver, cava
- Traditionally the contralateral kidney was explored – this can be omitted with CT
- Careful handling of the tumour to avoid spillage
- Tumour spill associated with higher rates of local recurrence, worse overall survival, and mandates intensification of chemotherapy
- Partial nephrectomy is not standard of care – smaller tumours found on screening may be amenable – only routinely used for bilateral tumours or single kidney
Chemotherapy for Wilms tumour:
- Vincristine and dactinomycin +/- doxorubicin
- Higher stage or less favourable may include cyclophosphamide, carboplatin and etoposide
Radiation for Wilms tumour:
- Whole abdominal radiation for spillage or any COG stage 3 (incl pre-op biopsy)
- Lung radiation for metastases
Prognosis
Good – 5 year survival of > 90 %.
Markers for worse prognosis:
- Higher stage
- Anaplastic histology
- Lung or liver metastases (although generally respond to chemo +/- XRT)
- Recurrent disease
There is no appreciable difference in survival for either treatment strategy – i.e. upfront nephrectomy or neoadjuvant chemotherapy.