Absence of immunoperoxidase staining for myoglobin in the malignant rhabdoid tumor of the kidney.

Malignant rhabdoid tumor of the kidney, a clinically and pathologically unique tumor of early childhood, has been recently distinguished from nephroblastoma. Skeletal muscle histogenesis has been considered because of its aggressive course and histologic resemblance to rhabdomyosarcoma. Application of an indirect immunoperoxidase technique for myoglobin, an early marker of myogenesis, failed to show the protein in four malignant rhabdoid tumors of kidney. This substantiates the lack of ultrastructural evidence of skeletal muscle differentiation in these tumors.