Sensitivity and specificity of cluster differentiation and friend leukemia integration1 for the diagnosis in a series of molecularly confirmed ewing sarcoma family of tumors

Abstract

Background: Immunohistochemistry (IHC) is a cost-effective and routinely available ancillary technique for the diagnosis of Ewing sarcoma family of tumors (ESFT). However, molecular confirmation is needed for precise diagnosis. Aim: This study aimed to determine the sensitivity and specificity of the commonly used IHC markers cluster differentiation (CD99) and friend leukemia integration1 (FLI1) in a series of molecularly confirmed ESFT. Materials and Methods: Retrospective review of the ESFT confirmed by either fluorescence in situ hybridization (FISH) or reverse transcriptase polymerase chain reaction (RT-PCR) during a period of 10 years was done. The demographic, clinical, and radiologic data were noted from medical records. The histology was reviewed with CD99, FLI1, and additional markers, wherever performed. The sensitivity and specificity of CD99 and FLI1 for the diagnosis of ESFT were calculated. Results: There were 72 ESFT patients in the study period, confirmed by FISH (EWSR1 rearrangement) in 53 and RT-PCR (EWS-FLI1) in 19. The female-to-male ratio was 1.06. The median age at diagnosis was 21 years. The cases included 22 skeletal and 50 extraskeletal sites. The positivity of CD99 and FLI1 was 98.46% and 94.83%, respectively, and both were positive in 55/72 (76.39%) cases. The sensitivity and specificity of CD99 were 98.46% and 20%, and those of FLI1 were 94.83% and 28.57%, respectively. Conclusion: Although the sensitivity for CD99 and FLI1 was high, the specificity was low toward the diagnosis of ESFT. The combined use of CD99 and FLI1 could confirm only 76.39% of molecularly confirmed ESFT, emphasizing the need for a precise diagnosis by molecular technique.