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 -

Ans. is 'c' i.e., Clear cell sarcoma Clear cell carcinoma is a histological subtype of Wilm's tumour which frequently metastasize to bone (hi conventional wilms's 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.