Test Catalog

Test ID: SS18F    
Synovial Sarcoma (SS), 18q11.2 (SS18 or SYT) Rearrangement, FISH, Tissue

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

Supporting the diagnosis of synovial sarcoma when used in conjunction with an anatomic pathology consultation

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 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.

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

Synovial sarcoma (SS) is a malignant soft tissue tumor that predominantly occurs in the lower limbs of children and young adults. This tumor accounts for approximately 5% to 10% of soft tissue tumors, has a poor prognosis, and may occur in other areas of the body such as the head and neck, heart, abdominal wall, mediastinum, and lung, in addition to the extremities. Histologically, SS is grouped either into the monophasic subtype consisting of mostly spindle cells or the biphasic subtype consisting of epithelial and spindle cells. Depending on the site of origin, the differential diagnosis of SS can include mesothelioma, fibrosarcoma, solitary fibrous tumor, leiomyosarcoma, malignant peripheral nerve sheath tumors, epithelioid sarcoma, and clear cell sarcoma. In addition, when the SS is poorly differentiated, the differential diagnosis broadens to include the small round-blue cell tumors (Ewing sarcoma, alveolar rhabdomyosarcoma, and neuroblastoma). Accurate diagnosis of SS is important for appropriate clinical management of patients. Although immunohistochemical markers can be helpful in the correct diagnosis of these various tumor types, recent molecular studies have shown the superior specificity of molecular makers in differentiating SS from other tumors.


A recurrent, tumor-specific translocation t(X;18)(p11.2;q11.2) is observed in approximately 90% of synovial sarcomas. A single gene, SS18 (SYT), has been implicated on 18q11.2, while 1 of 3 related genes, SSX1, SSX2, or infrequently SSX4, is usually involved on Xp11.2. The prevalence of SS18-SSX1 is about twice that of SS18-SSX2 in most studies. Detection of these transcripts is usually performed by reverse transcriptase-PCR (RT-PCR) (SYT / Synovial Sarcoma RT-PCR), which allows specific identification of SS18-SSX1 or SS18-SSX2. Identification of the SS18-SSX1 fusion is associated with an unfavorable outcome with significantly shorter overall survival when compared to the SS18-SSX2 fusion. Unfortunately, RT-PCR results may be equivocal or falsely negative due to many reasons such as when the available RNA is of poor quality or if a rare translocation partner is present. In these cases, FISH testing can be used to identify SS18 gene rearrangements in these tumors, which supports the diagnosis of SS.

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 SS18 (SYT) FISH probe.


A positive result suggests rearrangement of the SS18 (SYT) gene region at 18q11.2 and supports the diagnosis of synovial sarcoma (SS).


A negative result suggests no rearrangement of the SS18 (SYT) gene region at 18q11.2. However, this result does not exclude the diagnosis of SS.

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 US Food and Drug Administration and is best used as an adjunct to existing clinical and pathologic information.


Fixatives other than formalin (eg, Prefer, Bouin) may not be successful for FISH assays; however, nonformalin-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

FISH analysis was performed on 36 formalin-fixed, paraffin-embedded tissue samples including 14 synovial sarcoma (SS) tumors and 22 noncancerous control specimens or nonSS tumors. The normal controls were used to generate a normal cutoff for this assay. Using reverse transcriptase-PCR (RT-PCR) analysis, 11 SS tumors had the SSX1 translocation partner and 3 tumors had the SSX2 translocation partner. Rearrangement of SS18 was identified in all 14 SS specimens with 10 exhibiting the expected signal pattern and 4 with an atypical signal pattern.

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

1. World Health Organization Classification of Tumours. Pathology and Genetics of Tumours of Soft Tissue and Bone. Edited by CDM Fletcher, K Unni, F Mertens. IARC: Lyon 2002, pp 200-204

2. Sandberg AA, Bridge JA: Updates on the cytogenetics and tissue tumors. Synovial sarcoma. Cancer Genet Cytogenet 2002 Feb;133(1):1-23

3. Kokovic I, Bracko M, Golouh R, et al: Are there geographical chimeric transcripts in synovial sarcoma? Cancer Detect Prev 2004;28(4):294-301

4. dos Santos NR, de Bruijn DR, van Kessel AG: Molecular mechanisms underlying human synovial sarcoma development. Genes Chromosomes Cancer 2001 Jan;30(1):1-14