A 7 – year old boy with left renal mass had bone pain and was detected to have bone metastatic deposits. The most likely renal tumor is :
Clear cell carcinoma is a histological subtype of wilm’s tumor which frequently metastasize to bone (In conventional wilms's tumor bone metastasis is rare).
Histology of wilms tumor 

Wilms tumor is a complex mixed embryonal neoplasm, comprises three elements : -


Blastenia.
Mesenchyme.
Epithelium.


On the basis of outcome Wilms tumor has been classified into two histological subtypes.

Favorable histology :

It is the conventional form and carries good prognosis.
Comprises blastoma, epithelial and stromal elements.
Devoid of anaplasia or ectopia.
Brain and bone metastasis is rare.
Metastasis may occur to lung.

Unfavorable histology :


Characterized by marked enlargement of nuclei, hyperchromatism, and multipolar mitotic figures.
Anaplasia is present.
Clear cell sarcoma is a subtype of the unfavorable form and usually metastasizes to bone.

Note :

Rhabdoid tumor, which may metastatize to the brain, is no longer classified as a subtype of wilms tumor.
Favorable histology Wilms tumor
Renal cell carcinoma
Clear cell sarcoma
Rhabdoid tumor