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Named in honor of Max Wilms (who originally proposed the origin of mixed kidney tumors)

Originated from nephrogenic blastema

90% of kidney pediatric tumors

Frequently present WT1 alterations (11p13)

Associated with syndromes (10%): Beckwith-Wiedemann, Denysh-Drash, WAGR

Palpable Painless mass is usually the most frequent presentation

Well circumscribed, pseudo encapsulated, gray-tan. Can have cystic areas

Usually composed of 3 elements (triphasic): Blastema, epithelium, and stromal elements.

Blastema is the small-undifferentiated cell component

Epithelial elements usually consist in small tubules or rosette like structures, but also can have mucinous, glomerular o squamous differentiation

Stroma is usually embryonal mesenchyme type, but can have many types of differentiation

Some cases can have ANAPLASIA and this finding is associated with worse prognosis

Anaplasia is defined as nuclear hipercromasia, nuclei that are 3x bigger than the rest, and multipolar mitoses.