<prompt> 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 -Favorable histology Wilms tumorRenal cell carcinomaClear cell sarcomaRhabdoid tumor  <response>: Ans. is c i.e., Clear cell sarcoma Clear cell carcinoma is a histological subtype of Wilms tumour which frequently metastasize to bone hi conventional wilmss tumour bone metastasis is rare. Histology of wilms tumor o Wilms tumor is a complex mixed embryonal neoplasm, comprises three elements : ? i Blastema ii Mesenchyme iii Epithelium o On the basis of outcome Wilms tumor has been classified into two histological subtypes : ? 1. Favourable histology o It is the conventional form and carries good prognosis. o Comprises blastoma, epithelial and stromal elements. o Devoid of anaplasia or ectopia. o Brain and bone metastasis is rare. o Metastasis may occur to lung. 2. Unorable histology o Characterized by marked enlargement of nuclei, hyperchromatism, and multipolar mitotic figures. o Anaplasia is present. o Clear cell sarcoma is a subtype of the unorable form and usually metastasizes to bone. Note : o Rhabdoid tumor, which may metastatize to the brain, is no longer classified as a subtype of wilms tumor. 