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83361
cell tumors (Ewing sarcoma, alveolar rhabdomyosarcoma, and neuroblastoma). Accurate diagnosis of
SS is important for appropriate clinical management of patients. Although immunohistochemical (IHC)
markers can be helpful in the correct diagnosis of these various tumor types, recent molecular studies
have shown the superior specificity of molecular markers 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) (#83361 Synovial Sarcoma by Reverse
Transcriptase PCR, Paraffin), 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 18q11.2
SS18 gene rearrangements in these tumors, which supports the diagnosis of SS.
Useful For: As an aid in the diagnosis of synovial sarcoma when RT-PCR results are equivocal or do
not support the clinical picture
Interpretation: A neoplastic clone is detected when the percent of cells with an abnormality exceeds
the normal cutoff for the SYT FISH probe. A positive result suggests rearrangement of the SYT gene
region at 18q11.2 and supports the diagnosis of synovial sarcoma (SS). A negative result suggests no
rearrangement of the SYT gene region at 18q11.2. However, this result does not exclude the diagnosis of
SS.
Reference Values:
An interpretive report will be provided.
Clinical References: 1. Sandberg AA, Bridge JA: Updates on the cytogenetics and molecular
genetics of bone and soft tissue tumors. Synovial sarcoma. Cancer Genet Cytogenet 2002 Feb;133(1):1-23
2. Kokovic I, Bracko M, Golouh R, et al: Are there geographical differences in the frequency of
SYT-SSX1 and SYT-SSX2 chimeric transcripts in synovial sarcoma? Cancer Detect Prev
2004;28(4):294-301
Synovial Sarcoma by Reverse Transcriptase PCR (RT-PCR),
Paraffin
Clinical Information: Synovial sarcomas account for 9% to 10% of soft tissue tumors. These tumors
occur in 2 major forms: biphasic and monophasic. Monophasic tumors are composed entirely of spindle
cells, while biphasic tumors have epithelial cells arranged in glandular structures and mixed with spindle
cells. The tumors are usually positive for keratin and epithelial membrane antigen as well as vimentin by
immunostaining. Synovial sarcoma is a member the small-round-cell tumor group that includes
rhabdomyosarcoma, lymphoma, Wilms tumor, Ewing sarcoma, and desmoplastic small-round-cell tumor.
While treatment and prognosis depend on establishing the correct diagnosis, the diagnosis of sarcomas
that form the small-round-cell tumor group can be very difficult by light microscopic examination alone,
especially true when only small needle biopsy specimens are available for examination. The use of
immunohistochemical stains (eg, keratin and EMA) can assist in establishing the correct diagnosis, but
these markers are not entirely specific for synovial sarcoma. Expertise in soft tissue and bone pathology
are often needed. Studies have shown that some sarcomas have specific recurrent chromosomal
translocations. These translocations produce highly specific gene fusions that help define and characterize
subtypes of sarcomas and are useful in the diagnosis of these lesions.(1-4) Cytogenetic studies have
shown a distinctive chromosomal translocation, t(X;18)(p11;q11), in more than 90% of synovial
sarcomas. Cloning of the translocation breakpoint showed that t(X;18) results in the fusion of 2 genes
designated as SYT (at 18q11) and SSX (at Xp11). Two closely related genes, SSX1 and SSX2, have 81%
homology in proteins. SYT-SSX2 is present in 35% of cases. Patients with SYT-SSX2 translocation
usually have greater metastasis-free survival than those with SYT-SSX1. These fusion transcripts can be
detected by reverse transcriptase PCR (RT-PCR), by FISH, chromogenic in situ hybridization (CISH), or
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