ANTIBODIES TO DESMIN IDENTIFY THE BLASTEMAL COMPONENT OF NEPHROBLASTOMA

The blastemal component of Wilms' tumor (WT) might be indistinguishabl e histologically from other small, blue, round-cell tumors of childhoo d, including alveolar rhabdomyosarcoma (RMS), particularly in small bi opsy specimens and in the setting of metastatic disease, Furthermore, there are currently no reliable blastemal markers, Deparaffinized sect ions of 9 formalin-fixed blastema-predominant WTs and 46 RMSs were imm unostained with antibodies to desmin (D33), myogenin (F5D), MyoD1 (5.8 A), and muscle-specific actins (HHF35), after heat-induced epitope ret rieval. WE defined as positive those cases with more than 5% of cells immunostained (only nuclear staining was considered as positive for my ogenin and MyoD1). Antibodies to desmin were positive in eight (89%) o f nine cases of blastema-predominant WT; in contrast, no case was posi tive for any of the other muscle-associated proteins, Of the 46 cases of RMS, all were positive for desmin, 42 were positive for myogenin an d MyoD1, and 43 were positive for muscle actins. Desmin immunoreactivi ty, of and by itself, cannot be considered specific for RMS, but when accompanied by immunoreactivity for other myogenic proteins, it is hig hly characteristic of RMS, Our data also suggest that desmin immunorea ctivity, in the absence of other muscle-associated protein expression, might be considered a clue to the diagnosis of the blastemal WT, Part icularly in the context of small. biopsy specimens or in metastatic se ttings, the use of a panel of antibodies to desmin as well as to other myogenic proteins, such as MyoD1 or myogenin, can help to discriminat e between WT and RMS. Additional studies are required to determine whe ther desmin immunoreactivity in the blastemal component of WT represen ts true desmin expression.