Immunohistochemical validation of TLE1, a novel marker, for synovial sarcomas

Logistic and financial constraints limit application of several available immunohistochemical (IHC) markers and molecular analysis in every case of synovial sarcoma, diagnosed in our settings. Recently, TLE1 has been recognized as a robust IHC marker for diagnosing a synovial sarcoma. Here, we present IHC features of synovial sarcomas, including TLE1 expression in these cases and in some other tumours.

Conventional sections from 42 synovial sarcomas (30 retrospective & 12 prospectively diagnosed) were subjected to TLE1 IHC staining, including 21 tumours confirmed with molecular testing. TLE1 immunostaining was graded from 0, 1+, 2+, 3+, with 2+ or 3+ grades interpreted as positive staining.

Of the 42 tumours, 26 (61.9%) were of monophasic spindle cell type, 13 biphasic type (30.9%), two (4.7%) calcifying type and remaining one (2.3%) was a poorly differentiated synovial sarcoma. On immunohistochemistry (IHC), tumours were positive for epithelial membrane antigen (EMA) (26/34, 76.4%), cytokeratin (CK)7 (6/10, 60%), CK/MNF116 (6/21, 28.6%), B cell lymphoma 2 (BCL2) (36/37, 97.3%), cluster of differentiation molecule 99 (MIC2) (23/31, 74.1%) and transducin-like enhancer of split 1 (TLE1) (40/42, 95.2%), while negative for CD34 in all 21 tumours, wherever performed. TLE1 was also positive in tumour controls, including schwannomas (5/5, 100%), neurofibromas (2/2, 100%), malignant peripheral nerve sheath tumors (2/12, 17%) and Ewing sarcomas (4/10, 40%). TLE1 sensitivity for diagnosis of synovial sarcomas was 95.2 per cent. Its overall specificity was 63.7 per cent, whereas with regards to tumors forming its closest differential diagnoses, its specificity was 72 per cent.

Although molecular confirmation is the diagnostic gold standard for synovial sarcoma, TLE1, in view of its high sensitivity may be a useful marker within the optimal IHC panel comprising EMA, BCL2, MIC2, CD34 and CK7, especially on small biopsy samples, for substantiating a diagnosis of synovial sarcoma. Awareness of TLE1 expression in other tumours and its correct interpretation are necessary.