Molecular diagnosis of Ewing sarcoma family of tumors: a comparative analysis of 560 cases with FISH and RT-PCR.
OBJECTIVE
To compare the sensitivity and specificity of fluorescence in situ hybridization (FISH) with reverse transcription polymerase chain reaction (RT-PCR) in the diagnosis of Ewing sarcoma family of tumors (ESFTs) and other small round-cell tumors (SRCTs) in formalin-fixed paraffin-embedded tissue assembled in tissue microarrays (TMAs). The second objective is to confirm the value of molecular methods and immunohistochemical (IHC) assays, to perform a differential diagnosis between ESFTs and SRCTs with similar or overlapping morphology.


METHODS
A total of 560 cases were selected for the present study out the 806 cases collected from the PROgnosis and THerapeutic Targets in the Ewing's Family of TumorS project. Case selection bias included only the cases with enough material to enable the TMA construction, as FISH analysis and the majority of IHC studies were performed in TMAs. Histopathologic, IHC, and molecular assays were carried out.


RESULTS
Of the 560 total cases, 411 (73.4%) were considered informative (with results by FISH and/or RT-PCR assays). From the informative cases, 382 (92.9%) were diagnosed as ESFT, 23 cases (5.6%) as non-ESFT but with specific diagnosis for another established entity, and 6 cases (1.5%) as small round cell tumors not otherwise specified. Sensitivity and specificity for the FISH assays was 96.3% and 95.2%, respectively, whereas RT-PCR presented a sensitivity of 97.5% and specificity of 92.9%. In concordant cases, both methods showed a sensitivity and specificity of 99.2% and 100%, respectively. Twenty-nine cases (7.1%) initially interpreted at morphologic level as atypical ESFTs were finally reclassified, with the support of molecular methods and IHC, as either non-ESFT with another specific histologic type or as small round cell tumors not otherwise specified.


CONCLUSIONS
FISH and RT-PCR are ancillary techniques possessing high sensitivity in the diagnosis of ESFT; nevertheless, FISH is more specific than RT-PCR in the diagnosis of formalin-fixed paraffin-embedded tissue. Both methods in combination displayed the highest sensitivity and specificity. The combination of histopathologic, IHC, and molecular findings is the method of choice for the diagnosis of ESFT, as well as for the differential diagnosis with other SRCTs.
Department of Pathology, University of Valencia, Valencia, Spain.
Isidro
I
Machado
Rosa
R
Noguera
Antonio
A
Pellin
Jose A
JA
Lopez-Guerrero
Marta
M
Piqueras
Samuel
S
Navarro
Antonio
A
Llombart-Bosch
D014408:Biomarkers, Tumor / Q000032:analysis; D001859:Bone Neoplasms / Q000737:chemistry / Q000175:diagnosis* / Q000235:genetics; D004273:DNA, Neoplasm / Q000032:analysis; D006801:Humans; D017404:In Situ Hybridization, Fluorescence / Q000379:methods*; D025202:Molecular Diagnostic Techniques; D016612:Paraffin Embedding; D011237:Predictive Value of Tests; D012334:RNA, Neoplasm / Q000032:analysis; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000379:methods*; D012512:Sarcoma, Ewing / Q000737:chemistry / Q000175:diagnosis* / Q000235:genetics; D046888:Tissue Array Analysis; D014178:Translocation, Genetic
D014408:Biomarkers, Tumor; D004273:DNA, Neoplasm; D012334:RNA, Neoplasm