Test Catalog

Test ID: EWSF    
Ewing Sarcoma, 22q12 (EWSR1) Rearrangement, FISH, Tissue

Useful For Suggests clinical disorders or settings where the test may be helpful

Supporting the diagnosis of Ewing sarcoma (EWS)/primitive neuroectodermal tumor, myxoid chondrosarcoma, desmoplastic small, round cell tumor, clear cell sarcoma, and myxoid liposarcoma when used in conjunction with an anatomic pathology consultation


An aid in the diagnosis of EWS when reverse transcriptase-polymerase chain reaction results are equivocal or do not support the clinical picture

Testing Algorithm Delineates situations when tests are added to the initial order. This includes reflex and additional tests.

This test does not include a pathology consult. If a pathology consultation is requested, PATHC / Pathology Consultation should be ordered and the appropriate fluorescence in situ hybridization (FISH) test will be ordered and performed at an additional charge.


This test includes a charge for application of the first probe set (2 FISH probes) and professional interpretation of results. Additional charges will be incurred for all reflex probes performed. Analysis charges will be incurred based on the number of cells analyzed per probe set. If no cells are available for analysis, no analysis charges will be incurred.


See the Method Description for specific details.

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

Ewing sarcoma/primitive neuroectodermal tumors are members of the small, round cell group of tumors that are thought to originate in cells of primitive neuroectodermal origin with variable degrees of differentiation. The small, round cell group of tumors also includes rhabdomyosarcomas, desmoplastic small, round cell tumors, and poorly differentiated synovial sarcomas. Although immunohistochemical markers can be helpful in the correct diagnosis of these tumors, recent molecular studies have shown the specificity of molecular markers in differentiating specific subtypes of small, round blue-cell tumors. Accurate diagnosis of each tumor type is important for appropriate clinical management of patients.


Ewing tumors are characterized cytogenetically by rearrangements of the EWSR1 gene at 22q12 with FLI1 at 11q24 (t[11;22]) or ERG at 21q22 (t[21;22]) in 85% and 5% to 10% of Ewing tumors, respectively. Less than 1% of cases may have other fusion partners such as ETV1 at 7p22, E1AF at 17q12, or FEV at 2q33.

Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.

An interpretive report will be provided.

Interpretation Provides information to assist in interpretation of the test results

A neoplastic clone is detected when the percent of cells with an abnormality exceeds the normal cutoff for the EWSR1 FISH probe set.


A positive result is consistent with a diagnosis of Ewing sarcoma (EWS)/primitive neuroectodermal tumors (PNET).


A negative result suggests that a EWSR1 rearrangement is not present but does not exclude the diagnosis of EWS/PNET.

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

This test is not approved by the U.S. Food and Drug Administration and is best used as an adjunct to existing clinical and pathologic information.


Fixatives other than formalin (eg, Prefer, Bouin's) may not be successful for fluorescence in situ hybridization (FISH) assays, however non-formalin fixed samples will not be rejected. 


Paraffin-embedded tissues that have been decalcified are generally unsuccessful for FISH analysis. The pathologist reviewing the hematoxylin and eosin-stained slide may find it necessary to cancel testing.

Supportive Data

Fluorescence in situ hybridization analysis was performed on 38 formalin-fixed, paraffin-embedded tissue samples, including 16 tumors, and 22 noncancerous control specimens. The normal controls were used to generate a normal cutoff for this assay. Rearrangement of EWSR1 was identified in 14 tumor specimens and 2 yielded no results due to poor hybridization.

Clinical Reference Recommendations for in-depth reading of a clinical nature

1. Fletcher CDM, Unni KK, Mertens F, eds. World Health Organization Classification of Tumors. Pathology and Genetics Tumours of Soft Tissue and Bone.  IARC Press; 2002:298-300

2. Burchill SA: Ewing's sarcoma: diagnostic, prognostic, and therapeutic implications of molecular abnormalities. J Clin Pathol. 2003 February;56(2):96-102. doi: 10.1136/jcp.56.2.96

3. Riley RD, Burchill SA, Abrams KR, et al: A systematic review of molecular and biological markers in tumors of the Ewing's sarcoma family. Eur J Cancer. 2003 January;39:19-30. doi: 10.1016/s0959-8049(02)00500-2

4. Romeo S, Dei Tos AP: Soft tissue tumors associated with EWSR1 translocation. Virchows Arch. 2010 Feb;456(2):219-34. doi: 10.1007/s00428-009-0854-3