Increased C-MYC Oncogene Expression in Ewing's Sarcoma: Correlation with Ki67 Proliferation Index

Abstract

Aims and Background Ewing's sarcoma is a highly malignant musculoskeletal tumor composed of small round cells. Although important results have been achieved with surgery associated with chemotherapy, recurrent disease is still a major problem. In order to define new prognostic factors useful for therapeutic decision-making, we conducted a study on 38 Ewing's sarcoma samples in which c-myc oncogene expression and Ki67 proliferation index were correlated with clinical outcome. Methods and Study Design Nineteen patients developed metastases during follow-up and 10 of these patients died. C-myc and Ki67 protein expression was evaluated by immunohistochemistry performed on 5 μm formalin-fixed and paraffin-embedded sections, while the c-myc mRNA transcript was localized using in situ hybridization. Results A statistically positive correlation was found between c-myc protein and Ki67 (P = 0.001) and c-myc mRNA and Ki67 expression (P = 0.047). The 38 patients were divided into two groups using as the cutoff 50% of Ki67-positive cells. The disease-free survival and overall survival estimates were 68% and 90%, respectively, in the group of patients with a percentage of Ki67-positive cells <50%, and 25% and 50%, respectively, in the group with a percentage of Ki67-positive cells ≥50%. The difference between the survival curves was statistically significant (P <0.05 and P <0.01). Furthermore, relapsed patients had a high and uniform expression of c-myc protein and mRNA compared to disease-free patients. Conclusion These results suggest a possible role of the c-myc oncogene and Ki67 antigen in the malignant progression of Ewing's sarcoma.