Final Diagnosis -- Synovial Sarcoma


Synovial Sarcoma


Synovial sarcoma is a mesenchymal tumor composed of spindle cells that are intermixed with elements that feature epithelial differentiation, hence its characteristic biphasic appearance.[1] It can occur at any age, however its peak incidence is in the third decade.[2] Synovial sarcomas have a rather equal male:female incidence ratio.[1] Although it typically occurs in the extremities, usually near joints, it has also been reported in the trunk and head and neck regions.[2, 3] Rarer sites of involvement include kidney,[4] upper digestive tract,[5] heart,[6] male and female internal and external sex organs,[7, 8] among others.

Synovial sarcomas generally present as a tender mass that most of the times is larger than 5 cm[9] and grossly shows areas of hemorrhage or myxoid change admixed with tan-gray or pink areas that vary from soft to firm in consistency.[10] Microscopically these tumors are composed, of two main elements present in different proportions; one, a relatively monotonous population of spindle cells with granular chromatin, no visible nucleoli and high nuclear-to-cytoplasm ratio; and an epithelial cell population forming tubular, glandular or cord-like structures or present as solid nests. The epithelial cells generally present cuboid or columnar morphology with ovoid nuclei, vesicular chromatin and eosinophilic cytoplasm.[1]

Several malignant mesenchymal tumors such as liposarcomas, leiomyosarcomas, neurofibrosarcomas, and malignant fibrous histiocytoma have been reported involving the pelvis generally presenting as large tumors sometimes extending to pelvic viscera, representing true therapeutical challenges to surgeons and oncologists.[11] Although cases of synovial sarcoma occurring in the pelvis have also been reported[12, 13] other tumors occur in much higher frequency at this site in female patients and should therefore be considered in the clinical and radiological differential diagnosis. Such tumors include ovarian neoplasms of either germinal, surface epithelium, or sex-cord stromal cell origin, malignancies arising from the cervix and corpus of the uterus such as cervical carcinoma or endometrial stromal tumors, or less frequently in this age group malignant mixed müllerian tumors.

In our case the morphological features appreciated on routine H&E sections made the most frequent ovarian tumors, cervical carcinoma, and endometrial stromal tumors unlikely possibilities. The distinction between a possible malignant mixed müllerian tumor and a neoplasm of mesenchymal origin was achieved through the use of immunohistochemical stains that were negative for CD10, PAX8, WT1 and ER decreasing the probabilities of a mullerian origin,[14-17] and positive for CD99 which pointed to a potential soft tissue origin for the lesion. The combination of CD99 positivity in the spindle cells and cytokeratin (AE1/AE3, CAM 5.2) and non-cytokeratin (Ber-EP4 and EMA) markers of epithelial differentiation positive in the remainder component of the tumor enhanced its biphasic nature,[18] putting synovial sarcoma high in the list of differential diagnoses and distinguishing it from the monophasic variant of this tumor that generally shows only focal positivity for keratins.[19] Finally, the FISH results showed SS18 (SYT) gene rearrangement that is associated to the characteristic t(X;18) (p11.2; q11.2) translocation, found exclusively in synovial sarcomas providing optimal proof of this tumor identity.[20]


  1. WHO Classification of Tumours of Soft Tissue and Bone, 4th Edition edn. Lyon: International Agency for Research on Cancer (IARC); 2013.
  2. Sultan I, Rodriguez-Galindo C, Saab R et al: Comparing children and adults with synovial sarcoma in the Surveillance, Epidemiology, and End Results program, 1983 to 2005: an analysis of 1268 patients. Cancer 2009, 115(15):3537-3547.
  3. Amble FR, Olsen KD, Nascimento AG et al: Head and neck synovial cell sarcoma. Otolaryngol Head Neck Surg 1992, 107(5):631-637.
  4. Argani P, Faria PA, Epstein JI et al: Primary renal synovial sarcoma: molecular and morphologic delineation of an entity previously included among embryonal sarcomas of the kidney. Am J Surg Pathol 2000, 24(8):1087-1096.
  5. Billings SD, Meisner LF, Cummings OW et al: Synovial sarcoma of the upper digestive tract: a report of two cases with demonstration of the X;18 translocation by fluorescence in situ hybridization. Mod Pathol 2000, 13(1):68-76.
  6. Nicholson AG, Rigby M, Lincoln C et al: Synovial sarcoma of the heart. Histopathology 1997, 30(4):349-352.
  7. Iwasaki H, Ishiguro M, Ohjimi Y et al: Synovial sarcoma of the prostate with t(X;18)(p11.2;q11.2). Am J Surg Pathol 1999, 23(2):220-226.
  8. Nielsen GP, Shaw PA, Rosenberg AE et al: Synovial sarcoma of the vulva: a report of two cases. Mod Pathol 1996, 9(10):970-974.
  9. Michal M, Fanburg-Smith JC, Lasota J et al: Minute synovial sarcomas of the hands and feet: a clinicopathologic study of 21 tumors less than 1 cm. Am J Surg Pathol 2006, 30(6):721-726.
  10. Evans HL: Synovial sarcoma. A study of 23 biphasic and 17 probable monophasic examples. Pathol Annu 1980, 15(Pt 2):309-331.
  11. Lewis SJ, Wunder JS, Couture J et al: Soft tissue sarcomas involving the pelvis. J Surg Oncol 2001, 77(1):8-14; discussion 15.
  12. Theriot C, Hughes K, Mitchell J et al: Pelvic synovial sarcoma of unknown primary origin: case report and literature review. J Miss State Med Assoc 2013, 54(11):308-311, 313.
  13. Fisher C, Folpe AL, Hashimoto H et al: Intra-abdominal synovial sarcoma: a clinicopathological study. Histopathology 2004, 45(3):245-253.
  14. Soslow RA, Ali A, Oliva E: Mullerian adenosarcomas: an immunophenotypic analysis of 35 cases. Am J Surg Pathol 2008, 32(7):1013-1021.
  15. Franko A, Magliocco AM, Duan Q et al: WT1 immunoprofiling and comparison of malignant Mullerian mixed tumors of the female genital tract. Int J Gynecol Pathol 2010, 29(5):452-458.
  16. Liliac L, Carcangiu ML, Canevari S et al: The value of PAX8 and WT1 molecules in ovarian cancer diagnosis. Rom J Morphol Embryol 2013, 54(1):17-27.
  17. Mikami Y, Hata S, Kiyokawa T et al: Expression of CD10 in malignant mullerian mixed tumors and adenosarcomas: an immunohistochemical study. Mod Pathol 2002, 15(9):923-930.
  18. Olsen SH, Thomas DG, Lucas DR: Cluster analysis of immunohistochemical profiles in synovial sarcoma, malignant peripheral nerve sheath tumor, and Ewing sarcoma. Mod Pathol 2006, 19(5):659-668.
  19. Miettinen M, Limon J, Niezabitowski A et al: Patterns of keratin polypeptides in 110 biphasic, monophasic, and poorly differentiated synovial sarcomas. Virchows Arch 2000, 437(3):275-283.
  20. Ladanyi M, Antonescu CR, Leung DH et al: Impact of SYT-SSX fusion type on the clinical behavior of synovial sarcoma: a multi-institutional retrospective study of 243 patients. Cancer Res 2002, 62(1):135-140.

Contributed by Cecilia Lezcano, M.D. and David J. Dabbs, M.D.

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