Is TLE1 Expression Limited to Synovial Sarcoma? Our Experience at Shifa International Hospital, Pakistan.

INTRODUCTION: Synovial sarcoma (SS) accounts for 10-15 percent of adult soft tissue sarcomas. Transducin-like enhancer of split 1 (TLE1), a transcriptional repressor, is essential in hematopoiesis, neuronal differentiation, and terminal epithelial differentiation. TLE1 proteins inhibit Wnt signaling and other cell fate determination signals, and so have an established role in repressing differentiation. TLE1 has recently been shown to be a highly sensitive and relatively specific marker of SS.

MATERIALS AND METHODS: Study design is retrospective, descriptive. A total of 25 cases of SS and 28 of soft tissue lesions were retrieved from the record. TLE1 (clone 1F5) expression was evaluated and scored as negative (<5% of cells positive), 1+ (5-25% of cells positive), 2+ (26-50% of cells positive), or 3+ (>50 % of cells positive).

RESULT: Twenty-four out of twenty-five (96%) cases of SS showed 3+ TLE1 expression. One (4%) case of poorly differentiated SS showed 2+ positivity. 3+ TLE1 positivity was seen in one (100%) case each of infantile fibrosarcoma and low-grade fibromyxoid sarcoma, while two cases (100%) of schwannoma also showed 3+ positivity. All cases of solitary fibrous tumor) (n=2), clear cell sarcoma of tendons and aponeurosis (n=2), embryonal rhabdomyosarcoma (n=1), and de-differentiated liposarcoma (n=2) showed 2+ positivity. 1+ positivity was seen in alveolar soft part sarcoma (n=2), Ewing's sarcoma (n=4), undifferentiated pleomorphic sarcoma (n=1), myxoid liposarcoma (n=1) and malignant peripheral nerve sheath tumor (n=1). TLE1 was negative in all cases of chordomas (n=2), lipomas (n=2), nodular fasciitis (n=2), malignant perivascular epithelioid cell tumor (n=1) and dermatofibrosarcoma protuberans (n=1).

CONCLUSION: TLE1 may be a reliable immunostain for diagnosing SS, but its expression is not limited to SS. Its expression should be interpreted in the light of morphological features and a panel of antibodies.