PET-CT imaging features that differentiate between positive and negative EWSR1 translocation in Ewing sarcoma

Ewing sarcoma breakpoint region 1 (EWSR1) translocation-negative tumors represent a minor portion of small round cell tumors consistent with Ewing sarcoma morphology. The purpose of this study was to differentiate EWSR1 translocation-positive tumors from EWSR1 translocation-negative tumors using PET-computed tomography features.

In this retrospective study 27, Ewing sarcoma patients (December 2011 to November 2016) were divided into two groups, EWSR1 translocation-positive and EWSR1 translocation-negative based on cytogenetic analysis. Pretreatment standardized uptake value maximum (SUVmax) and Hounsfield Units (HU) were measured in the primary tumor in the axial slice with the largest tumor diameter.The associations between SUVmax, HU and the presence of EWSR1 translocation were evaluated. Receiver operating characteristic curve analysis was used to determine cut-off levels of SUVmax and HU suggestive of EWSR1-negative tumors.

Twenty-one patients were classified as EWSR1-positive and six as EWSR1-negative. Eighteen had SUVmax and 21 had HU measurements. EWSR1-negative tumors had significantly higher SUVmax values (P = 0.003) and significantly lower HU values (P = 0.008). Receiver operating characteristic curve analysis showed that SUVmax had diagnostic ability to discriminate between EWSR1-negative and EWSR1-positive tumors (area under the curve = 0.964, P = 0.006). A SUVmax of at least 10 had a sensitivity of 100% and specificity of 85.7% for EWSR1-negative tumors. HU had lower diagnostic ability than SUVmax (area under the curve = 0.881, P = 0.012). A HU up to 57 had a sensitivity of 81.3% and specificity of 80.0% for EWSR1-negative tumors.

Higher SUVmax and lower HU may differentiate between EWSR1-positive and EWSR1-negative tumors. This may reflect EWSR1-negative tumor aggressiveness.