Renal sarcomas of childhood. A clinicopathologic and ultrastructural study.

Of 230 consecutive primary renal tumors of childhood collected over a 26-year period, 19 (8.2%) were sarcomas. The histologic criteria devised by the National Wilms' Tumor Study for diagnosis of "sarcomatous variants" of Wilms' tumor could be applied to all but three cases, namely, a rhabdomyosarcoma, a spindle-celled tumor, possibly leiomyosarcoma, and an unclassified primitive tumor. The most prevalent subtype was the bone-metastasizing, "clear cell" sarcoma. Correlative histologic and ultrastructural study supports the concept of subsets of tumors within the category now called "sarcomatous Wilms' tumor." Although this designation has the practical value of alerting the oncologist to the need for aggressive therapy, an origin in nephrogenic mesoderm cannot be cogently proposed for all of these tumors. This study also shows that the histologic features of the different subtypes of renal sarcomas may overlap. Hence, electron microscopy is indispensable for appropriate subclassification of these tumors.