Objective:To investigate the expressions of MyoD1 and Myogenin in rhabdomyosarcoma(RMS)and other small cell malignant tumors of childhood

so as to approach their clinical significance.Methods:11 cases of embryonal rhabdomyosarcoma(ERMS)

5 cases of alveolar rhabdomyosarcoma(ARMS)

10 cases of neuroblastoma

10 cases of malignant lymphoma and 10 cases of Ewing’s sarcoma were collected and stained with HE staining

to detect the expression levels of MyoD1 and Myogenin proteins by S-P immunohistochemistry method in these 4 types of small cell malignant tumors.Results:The positive expressions of MyoD1 and Myogenin in RMS were 75% and 68.75% respectively

but the expression rates in the other 3 types of small cell malignant tumors were 0%.The positive expression rates and intensity of MyoD1 and Myogenin in RMS group were higher than those in the other 3 types of small cell malignant tumors significantly(P<0.05).The positive expression rates of these 2 proteins in ARMS were higher than in ERMS(P<0.05).The higher malignant level was

the higher the positive expressions of MyoD1 and myogenin showed(P<0.05).The positive expressive rates of these 2 types of proteins in bad prognosis group were higher than those in middle prognosis group(P<0.05).Conclusion:The obvious expression difference between MyoD1 and Myogenin in RMS and in the other 3 types of small cell malignant tumors can be used as an index that distinguishes RMS with other small cell malignant tumors.MyoD1 and Myogenin can be a combination index of auxiliary diagnosis in RMS

providing significant and additional molecular biological methods to pathological diagnosis.