Test Catalog

Test ID: SSX18    
Synovial Sarcoma Panel, Technical Component Only

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

Aiding in distinguishing synovial sarcomas from similar sarcomas

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

For the initial technical component only immunohistochemical (IHC) stain performed, the appropriate bill-only test ID will be reflexed and charged (IHTOI). For each additional technical component only IHC stain performed, an additional bill-only test ID will be reflexed and charged (IHTOA).

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

SS18-SSX fusion-specific antibody and SSX-C-terminal antibody are markers used for the diagnosis of synovial sarcoma.


SS18-SSX fusion-specific antibody recognizes SS18-SSX fusion proteins which are a result of the SS18 (synovial sarcoma translocation, chromosome 18) gene fusing with SSX (synovial sarcoma, X) gene on chromosome 18. This translocation is unique to synovial sarcoma. SSX-C-terminal antibody recognizes endogenous levels of SSX (1-4) proteins and the SS18-SSX fusion protein. Using these two antibodies together will aid in distinguishing synovial sarcomas from other histologically similar sarcomas.

Interpretation Provides information to assist in interpretation of the test results

This test does not include pathologist interpretation only technical performance of the stain. If interpretation is required, order PATHC / Pathology Consultation for a full diagnostic evaluation or second opinion of the case.


The positive and negative controls are verified as showing appropriate immunoreactivity and documentation is retained at Mayo Clinic Rochester. If a control tissue is not included on the slide, a scanned image of the relevant quality control tissue is available upon request; call 855-516-8404.


Interpretation of this test should be performed in the context of the patient's clinical history and other diagnostic tests by a qualified pathologist.

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

Age of a cut paraffin section can affect immunoreactivity. Stability thresholds vary widely among published literature and are antigen dependent. Best practice is for paraffin sections to be cut within 6 weeks.

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

1. Baranov E, McBride M, Bellizzi A, et al: A novel SS18-SSX fusion-specific antibody for the diagnosis of synovial sarcoma. Am J Surg Pathol. 2020 Jul;44(7):922-933

2. Kadoch C, Crabtree G: Reversible disruption of mSWI/SNF (BAF) complexes by the SS18-SSX oncogenic fusion in synovial sarcoma. Cell. 2013 Mar 28;153(1):71-85

3. McBride M, Pulice J, Beird H, et al: The SS18-SSX fusion oncoprotein hijacks BAF complex targeting and function to drive synovial sarcoma. Cancer Cell. 2018 Jun 11;33(6):1128-1141

4. Thway K, Fisher C: Synovial sarcoma: defining features and diagnostic evolution. Annals of Diag Path. 2014 Dec;18(6):369-380