A distinctive pediatric renal neoplasm characterized by epithelioid morphology, basement membrane production, focal HMB45 immunoreactivity, and t(6;11)(p21.1;q12) chromosome translocation

We report two cases of a hitherto undescribed pediatric renal neoplasm that is distinctive at the morphological, immunohistochemical, ultrastructural, and cytogenetic levels. On light microscopy, the tumors are composed of ne sts of polygonal, clear to eosinophilic cells associated with a subpopulati on of smaller cells that surround hyaline material. Despite their epithelio id morphology, these tumors do not label immunohistochemically for epitheli al markers but instead label focally for melanocytic markers HMB45 and Mela n A. The hyaline material is positive with periodic acid-Schiff and methena mine-silver histochemical stains, and labels immunohistochemically for type 4 collagen. Ultrastructural examination confirms that it represents baseme nt membrane material. Cytogenetic analysis reveals the identical t(6; 11)(p 21.1;q12) chromosome translocation as the sole abnormality in these two tum ors, confirming their identity and distinctive nature.