[440] The Utility of TLE1 as a Diagnostic Marker for Synovial Sarcoma Sampled by Fine Needle Aspiration.

Matthew Stachler, Jason Hornick, Xiaohua Qian. Brigham and Woman's Hospital, Harvard Medical School, Boston, MA

Background: Synovial sarcoma (SS) is an aggressive malignant soft tissue tumor that may also occur in visceral organs and mediastinum and is often evaluated by fine needle aspiration biopsy (FNAB). The presence of diverse histologic patterns of SS (biphasic, monophasic and poorly differentiated) can make diagnosing SS challenging, especially in small FNAB. Recent studies have shown that TLE1, a transcriptional co-repressor implicated in hematopoiesis, neuronal and terminal epithelial differentiation, is a promising diagnostic maker for SS in surgical specimens. In this study, we evaluated the utility of TLE1 immunohistochemistry in distinguishing SS from its morphologic mimics in FNAB samples.
Design: In total, 9 FNAB cases of SS with cell blocks were evaluated, in addition to 25 cases of tumors in the differential diagnosis of SS: 5 thymomas, 8 peripheral nerve sheath tumors (PNST) (7 schwannomas and 1 malignant), 4 solitary fibrous tumors (SFT), 6 Ewing sarcomas (EWS), 1 dermatofibrosarcoma protuberans (DFSP) and 1 dedifferentiated liposarcoma (DDLPS). All diagnoses were confirmed by surgical resection and/or cytogenetic studies. Immunohistochemistry was performed on cell block sections using a polyclonal anti-TLE1 antibody. The extent of immunoreactivity was graded according to the percentage of tumor cells showing nuclear staining (>50%, 3+; 25-50%, 2+; <25%, 1+; no staining, 0) and the intensity of staining (strong, moderate, or weak).
Results: Strong nuclear expression of TLE1 was seen in 100% of SS cases, with 89% showing 3+ staining and all showing at least 2+ staining. Variable TLE1 staining was observed in 50% of PNSTs (12.5% 3+, 37.5% 1+ with 12.5% strong, 25% moderate, and 12.5% weak intensity). Weak to moderate TLE1 staining was seen in 75% of SFTs (25% 2+, 50% 1+ with 50% moderate and 25% weak intensity). Very limited TLE1 staining was observed in 20% of thymomas (1+, weak). EWS, DFSP and DDLPS were completely negative for TLE1.
Conclusions: TLE1 is a highly sensitive but not a completely specific marker for SS in FNA samples. Depending on the subtype of synovial sarcoma and the differential diagnosis, strong diffuse TLE1 nuclear expression can help distinguish SS from morphologic mimics such as thymoma, EWS and DFSP. However, caution must be taken for the interpretation of moderate TLE1 staining in samples containing a monomorphic spindle cell population when SFT or PNSTs are in the differential diagnosis. In such cases, molecular/cytogenetic confirmation of the SYT-SSX fusion gene is advisable.
Category: Cytopathology

Wednesday, March 2, 2011 1:00 PM

Poster Session VI # 88, Wednesday Afternoon

 

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