Histology and grading are important prognostic factors in synovial sarcoma

Abstract

Introduction: The diagnosis of synovial sarcoma (SS) is currently based on clinical, morphological, immunohistochemical and cytogenetic data. Some of these factors such as grade and histology, specific translocations (SS18-SSX1 vs. SS18-SSX2) and the reduced expression of INI1, were proposed as prognostic variables. The aim of this study was to verify whether histological (grading and histology) and molecular (type of SSX translocation and INI1 expression) characteristics of SS influence the prognosis of the disease.

Material and methods: We retrospectively evaluated 196 patients affected by SS of the extremities treated at our Institution (Istituto Ortopedico Rizzoli, Bologna, Italy). All cases were histologically revised and tumor grade was assessed according to the FNLCC system. Tissue specimens were retrospectively evaluated to check for SS18-SSX fusion type and INI1 expression.

Results: Most SS were monophasic, 28% were biphasic. Eighty tumors (41%) were grade 3. Sixty percent harbored SSX1 translocation, 40% SSX2; 51% maintained the expression of INI1. Sarcoma specific survival (OS) was 56.6% at 5 years and 46.9% at 10 years. Prognosis was worse in those patients monophasic SS (p = 0.011) as in those with a grade 3 tumors (p = 0.083). No correlation was found neither between SSX fusion type nor INI1 expression and survival. LR-free survival was 78.9% at 5 years and 75.9% at 10 years. A higher LR rate was observed in tumors with SSX2 translocation and (p = 0.049) in grade 3 SS (0 = 0.028).

Discussion: Our data confirm that not all cases of SS present the same severe outcome. High-risk patients identified on the basis of these parameters may qualify for an aggressive treatment approach.

Keywords: Grading; Histologic subtype; Prognostic factors; SS18-SSX fusion type; Synovial sarcoma.