BACKGROUND: Ewing's sarcoma tumor is an aggressive malignancy of bone and soft 
tissue in children and young adults. Despite advances in modern therapy, 
metastasis occurs and results in high mortality. Intracellular molecules Yap, 
Akt, mTOR, and Erk are signaling pathway members that regulate the proliferation 
of tumor cells.
OBJECTIVE AND METHODS: We studied the immunohistochemical expression of these 
proteins in 36 tumor samples from adult and pediatric patients with Ewing's 
sarcoma tumors. Patients' age, sex, tumor site, tumor size, clinical stage and 
survival (overall and disease-free survival) were collected. Tissue microarrays 
slides were stained with antibodies against Yap, Akt, mTOR, and Erk proteins.
RESULTS: Tumors exhibited variable expression of Yap, Akt, mTOR, and Erk (from 
negative, low to high), with high levels of expression present in 31%, 53%, 77% 
and 0% respectively. Immunohistochemical expression of Akt was associated with 
worse overall and disease-free survival (p<0.05). The other biomarkers did not 
demonstrate any difference in survival between low versus high expression.
CONCLUSION: Although Yap, Akt, mTOR, and Erk protein are all expressed in 
Ewing's sarcoma by immunohistochemistry, only Akt expression is associated with 
worse prognosis. Larger studies are needed to verify these results and plan 
targeted therapy, particularly against Akt.