[77] Immunohistochemical Staining for TLE1 Distinguishes Synovial Sarcoma from Histologic Mimics

WC Foo, MR Wick, JL Hornick. Brigham and Women's Hospital, Harvard Medical School, Boston, MA; University of Virginia Medical Center, Charlottesville, VA

Background: TLE1, a transcriptional corepressor implicated in hematopoiesis and epithelial differentiation, is overexpressed in synovial sarcomas. Recent studies evaluating its utility as a diagnostic marker have reported conflicting results. We investigated TLE1 expression by immunohistochemistry in a well-characterized series of synovial sarcomas and other mesenchymal tumors most commonly considered in the differential diagnosis.
Design: Whole tissue sections of 171 tumors were evaluated: 54 synovial sarcomas (21 biphasic, 18 monophasic, 15 poorly differentiated), 40 malignant peripheral nerve sheath tumors (MPNST; all positive for S100 and/or arising in patients with type 1 neurofibromatosis), 40 solitary fibrous tumors (20 typical and 20 histologically malignant, defined by mitotic activity), 20 fibrosarcomatous variant of dermatofibrosarcoma protuberans, and 17 Ewing sarcoma/primitive neuroectodermal tumors (PNET). All monophasic and poorly differentiated synovial sarcoma and Ewing sarcoma/PNET cases were previously confirmed to harbor t(X;18) or EWSR1 gene rearrangement, respectively. Immunohistochemical studies were performed following pressure cooker antigen retrieval using a polyclonal anti-TLE1 antibody (1:400; Santa Cruz). The extent of immunoreactivity was graded according to the percentage of tumor cells showing nuclear staining: 0, no staining; 1+, <5%; 2+, 5-25%; 3+, 26-50%; 4+, 51-75%; or 5+, 76-100%; and the intensity of staining was graded as weak, moderate, or strong.
Results: In total, 41 of 54 (76%) synovial sarcoma cases showed TLE1 positivity, including 16 (76%) biphasic (5+ [4], 4+ [2], 3+ [3], 2+ [3], 1+ [4]; weak [9], moderate [6], strong [1]), 12 (67%) monophasic (5+ [4], 4+ [3], 3+ [0], 2+ [5], 1+ [0]; weak [5], moderate [5], strong [2]), and 13 (87%) poorly differentiated (5+ [6], 4+ [2], 3+ [1], 2+ [3], 1+ [1]; weak [1], moderate [6], strong [6]). Of the other tumor types evaluated, only 4 (10%) MPNSTs were positive for TLE1 (3+ [1], 2+ [2], 1+ [1]; weak [2], moderate [2]). All of the other tumors were completely negative for TLE1.
Conclusions: TLE1 is a sensitive and highly specific marker for synovial sarcoma and can be helpful to distinguish synovial sarcoma from histologic mimics. In this study, only a small subset of MPNST showed limited staining for TLE1.
Category: Bone & Soft Tissue

Tuesday, March 23, 2010 9:30 AM

Poster Session III # 6, Tuesday Morning

 

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