Malignant small round cell tumors usually progress rapidly and show resistance to chemotherapy, and it is often difficult to make a definitive diagnosis based on their histological morphology. Glypican-3 (GPC3) is a highly tumor-specific antigen, and the overexpression of GPC3 was reported in many pediatric and adult malignancies. In the present study, we investigated the GPC3 expression in pediatric malignant small round cell tumors to assess its role in the differential diagnosis of the tumors. Immunohistochemistry was performed to assess the expression of GPC3 in samples from 84 rhabdomyosarcomas (RMSs; 44 alveolar and 40 embryonal RMSs), 62 Ewing sarcomas (EWSs), 35 neuroblastomas (NBs) and two desmoplastic small round cell tumors (DSRCTs). We performed a reverse transcription-quantitative polymerase chain reaction for GPC3 to determine the GPC3 mRNA expression in samples from 66 frozen tumors (23 RMSs, 28 EWSs and 15 NBs). The serum expression levels of GPC3 were analyzed in pre-operative blood samples from two RMS and eight NB patients. In total, 25% (21/84) of the RMSs and 3% (1/35) of the NBs exhibited a focal expression of GPC3, whereas, the other specimens showed no GPC3 expression. The GPC3 mRNA expression level of the RMSs with positive GPC3 expression (n=6) was significantly higher compared with the RMSs without such expression (n=17). A total of two cases of NB showed high serum levels of GPC3, but neither tumor showed immunoreactivity for GPC3. The immunohistochemical overexpression of GPC3 may be a candidate ancillary parameter in the differential diagnosis of RMS from EWS and DSRCT.
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