POLYMERASE CHAIN REACTION-BASED DIAGNOSIS OF RHABDOMYOSARCOMAS - COMPARISON OF FETAL TYPE ACETYLCHOLINE-RECEPTOR SUBUNITS AND MYOGENIN

The diagnosis of rhabdomyosarcoma (RMS) is usually straightforward whe n light microscopy and immunohistochemistry are used. However, tumors that exhibit a low degree of differentiation and small biopsies can le ad to confusion. In such patients and for the detection of minimal (re sidual) disease, a polymerase chain reaction (PCR)-based approach woul d be a valuable diagnostic adjunct. This type of approach would be hig hly sensitive and should be free from the risk for contamination of th e tumor sample with normal tissue. Because myogenin and the alpha and gamma subunit of the fetal type acetylcholine receptor (AChR) are spec ific immunohistochemical markers for RMS, their expression on the mRNA level in RMS, other childhood and adult tumors, and normal tissues wa s studied. Although the sensitivity of both approaches was 100% in emb ryonal and alveolar RMS, detection of myogenin mRNA was not specific f or RMS but occurred in normal muscle and the majority of the other nor mal tissues and childhood tumors. Conversely, detection of fetal AChR mRNA as defined by an alpha/tau ratio of <1 was encountered only in RM S and denervated muscle. The authors conclude that mRNA of the fetal t ype AChR but not myogenin is a highly specific and sensitive target fo r the PCR-based diagnosis of RMS.