Cytohistologic correlations in 56 synovial sarcomas in 36 patients: the Institut Curie experience

Synovial sarcoma (SS) is a high-grade malignant soft tissue tumor that manifests different phenotypic subtypes that may render their cytologic evaluation challenging. Although several cytologic studies of SS have been published, correlative studies of cytologic and corresponding histologic features are limited. To better define the cytological features of various SS forms, we reviewed the cytologic and the corresponding histologic material of 56 tumors from 36 patients. Classical patterns were defined as dispersed or small clusters of cells with bland chromatin, inconspicuous nucleoli, oval to spindle-shaped cytoplasm and branching tumor tissue fragments, vessel stalks, acinar structures in scant mucin background, seen in all 53 (94.7%) cellular cases. Epithelial, squamous, round cells, mast cells, necrosis, comma-like nuclei, marked nuclear atypia, secretory mucin, and rosette-like structures were also occasionally observed. Comparing the histological subtype we noted that epithelial cells and secretory mucin were restricted to biphasic SS, round cells to poorly differentiated SS, and comma-like nuclei to monophasic fibrous SS. We conclude that the classical pattern is highly suggestive of SS of all three monophasic, biphasic, or poorly differentiated subtypes. These characteristics, along with molecular genetic studies, may improve the cytologic diagnosis of SS.