Original ArticlePrimary Intrathoracic Synovial Sarcoma A Clinicopathologic Study of 40 t(X;18)-Positive Cases From the French Sarcoma Group and the Mesopath GroupBégueret, Hugues, MD*; Galateau-Salle, Françoise, MD†; Guillou, Louis, MD‡‡; Chetaille, Bruno, MD‡; Brambilla, Elisabeth, MD§; Vignaud, Jean-Michel, MD∥; Terrier, Philippe, MD¶; Groussard, Odile, MD**; Coindre, Jean-Michel, MD††Author Information From the Departments of Pathology, *Hôpital Haut-Lévêque, Pessac, †Centre Hospitalo-Universitaire, Caen, ‡Hôpital de la Timone, Marseille, §Hôpital Albert Michallon, Grenoble, ∥Hôpital Central, Nancy, ¶Institut Gustave Roussy, Villejuif, **Hôpital Beaujon, Clichy, ††Institut Bergonié, Bordeaux, France; and ‡‡Institut Universitaire de Pathologie, Lausanne, Switzerland. Supported by the Ligue Nationale Contre la Cancer, Committees of Charente-Maritime, Gironde and Landes. Reprints: Jean-Michel Coindre, MD, Department of Pathology, Institut Bergonié, 229 Cours de l'Argonne, 33076 Bordeaux Cédex, France (e-mail: firstname.lastname@example.org). The American Journal of Surgical Pathology: March 2005 - Volume 29 - Issue 3 - p 339-346 doi: 10.1097/01.pas.0000147401.95391.9a Buy Metrics Abstract Synovial sarcoma (SS), an aggressive neoplasm accounting for up to 14% of soft tissue sarcomas, was recently recognized as a primary tumor in the lung and pleura. SS is characterized by the chromosomal translocation t(X;18)(SYT-SSX) found in more than 95% of the tumors. We report a cooperative study from the French Sarcoma Group and the Mesopath Group on 40 t(X;18)(SYT-SSX)-positive primary intrathoracic SS. There were 22 males and 18 females, whose age ranged from 16 to 79 years (median, 47 years). Neoplasms were mostly circumscribed and of large size (median, 7.5 cm; range, 2-16 cm). Thirty-nine tumors were monophasic SS, including 24 (60%) monophasic fibrous and 15 (37.5%) poorly differentiated cases, and one lesion was a biphasic SS. A larger proportion of poorly differentiated tumors were observed among intrathoracic SS as compared with soft tissue SS. Immunohistochemically, 90% of the cases reacted with at least one epithelial marker. CD34 was focally expressed in 3 cases. SYT-SSX1 fusion transcripts were detected in 22 cases (56.4%) and SYT-SSX2 fusion transcripts in 17 cases. Median and 5-year disease-specific survival in 33 patients was 50 months and 31.6%. Median and 5-year disease-free survival was 24 months and 20.9%. Patient sex, age, tumor size, histologic subtype, grade, and SYS-SSX fusion type had no significant impact on outcome. In conclusion, intrathoracic SS are rare but aggressive tumors with poor prognosis. In this unusual location, the detection of SYT-SSX fusion transcripts is a valuable diagnostic adjunct. © 2005 Lippincott Williams & Wilkins, Inc.