Wilms’ tumor

Children’s Oncology Group (COG) histologic classification ⁽¹⁾

Favorable histology Wilms’ tumor

• No evidence of anaplasia

Un-favorable histology Wilms’ tumor

a.    Focal anaplastic Wilms’ tumor

• Anaplasia confined to one or more discrete sites within the primary tumor with no extrarenal involvement
• No nuclear unrest outside anaplastic foci

b.    Diffuse anaplastic Wilms’ tumor

• Non-localized anaplasia
• Anaplasia in invasive sites or extrarenal deposits
• Localized anaplasia with severe nuclear unrest
• Anaplasia in a random biopsy specimen
• Anaplasia involving the edge of one or more sections.

Blastemal predominant histology (post chemotherapy) ⁽²⁾

▪️  Presence of residual undifferentiated blastemal cells of over 66% in a tumour with more than 33% of cells viable after preoperative chemotherapy^.

Risk group definition for patients with favorable histology WT ⁽³⁾

Low risk:                                                                                      

▪️  Stages I-II.

Standard risk:

▪️ Stage III.

▪️   Stage IV (pulmonary metastasis only) and RCR post week 6.

High risk:

▪️ Stage IV (pulmonary metastasis only) with SIR post week 6.

▪️  Stage IV (extra pulmonary metastasis).

Response criteria for stage IV favorable histology with pulmonary metastasis: ⁽⁴⁾

Rapid complete responder (RCR): complete resolution of pulmonary metastases after 6 weeks of pre-nephrectomy chemotherapy with vincristine, dactinomycin, and doxorubicin.

Slow incomplete responder (SIR): incomplete resolution of pulmonary metastases after 6 weeks of pre-nephrectomy chemotherapy with vincristine, dactinomycin, and doxorubicin.

Risk stratification at relapse definitions: ⁽⁵⁾

• Standard risk: patients with initial stage I−II low-risk or intermediate-risk tumours, who received only vincristine and/or actinomycin D (no radiotherapy) in their first-line treatment.
• High risk: Patients without initial diffuse anaplasia or blastemal-type histology, who have already received doxorubicin in their initial treatment.
• Very high risk: Patients with recurrent anaplastic or blastemal-predominant tumor.