Identification of factors to detect
chemotherapy-resistant tumours at diagnosis is a first priority for risk-adapted
therapy in the oncology of children and young adults, where more individualized, effective, and less toxic treatments are highly desirable. In this study, we analysed the
miRNAs discriminating
Ewing's sarcoma (EWS) patients with different clinical outcomes in order to identify new indicators of prognosis.
miRNA expression was investigated in 49 primary EWSs by using the Agilent human
miRNA microarray v.2 and/or qRT-PCR. Statistical power of the samples studied for
miRNA expression was verified, indicating adequate sample size. Microarray analysis defined a signature of five
miRNAs (miR-34a, miR-23a, miR-92a, miR-490-3p, and miR-130b) as an independent predictor of risk for
disease progression and survival. Validation analysis in the extended sample set indicated that both miR-34a and miR-490-3p achieved sufficient statistical power to predict prognosis. Results were particularly robust for miR-34a, which appeared associated with either event-free or overall survival and emerged as a significant predictor also after multivariate analysis. Patients with the highest expression of miR-34a did not experience adverse events in 5 years; in contrast, patients with the lowest expression recurred within 2 years. High expression of miR34a can be detected also in
paraffin-embedded tissues by in situ hybridization, thus contributing to an easy routine evaluation of this
miRNA. Functional analysis of miR-34a in EWS cell lines indicated that when miR-34a expression was enforced, cells were less proliferative, less malignant, and sensitized to
doxorubicin and
vincristine. Expression of miR-34a could be increased in p53wt cells by treatment with
nutlin-3a. Accordingly,
nutlin-3a synergizes with
doxorubicin. Overall, our data indicate that miR-34a expression is a strong predictor of outcome in EWS. Restoration of miR-34a activity may be useful to decrease
malignancy and increase tumour sensitivity to current drugs, so sparing excessive long-term toxicity to EWS patients.