PEDIATRIC RHABDOMYOSARCOMAS EXPRESS THE INTERMEDIATE FILAMENT NESTIN

Previous findings that the intermediate filament nestin is expressed i n immature skeletal muscle cells prompted us to compare the staining p atterns of nestin and desmin in rhabdomyosarcomas (RMSs) and in other small cell tumors of infancy. We found that nestin immunoreactivity wa s present in all of 29 examined typical RMSs, which also expressed des min. Two undifferentiated tumors, primarily suspected to be RMSs, expr essed nestin, but not desmin. One of these nestin-positive, desmin-neg ative tumors was positive for the expression of the myogenic regulator y gene MyoD and is considered to represent an undifferentiated RMS. Th e other, a paratesticular tumor, did not contain transcripts for MyoD, and most likely does not represent a RMS. In several RMSs and nonmusc le tumors, a z-disc-associated nestin immunoreactivity occurred as a p aramalignant phenomenon in cross-striated muscle fibers adjacent to th e tumor cells. Our findings indicate that nestin, although present als o in tumors of the central and peripheral nervous systems, as well as in endothelial cells and in some muscle cells adjacent to tumors, is a useful complementary marker for RMS, particularly in very undifferent iated desmin-negative tumors.