A Study on Stat6 Expression in Solitary Fibrous Tumour

Abstract

BACKGROUND Solitary Fibrous Tumour (SFT) is an uncommon mesenchymal neoplasm of fibroblastic type arising anywhere in the body. Classic SFTs show neoplastic cells arranged in a pattern of less architecture with alternating hypo and hypercellular areas and prominent branching vasculature. Traditionally, CD-34 expression is the most consistent finding in SFTs, however this expression is also common in other tumours that may mimic SFT. Recently, a recurrent gene fusion NAB2-STAT6 has been identified as molecular hallmark of SFT. Molecular detection of the fusion gene and immunohistochemical expression of nuclear STAT6 can be helpful in diagnosing SFT. Aim-To study the expression of STAT6 in SFT. MATERIALS AND METHODS 23 cases of SFT diagnosed during a 2-year period. STAT6 immunohistochemistry was performed on 18 SFT cases and also on 8 possible mimickers of SFT, which were taken as the (negative) control. RESULTS Nuclear STAT6 positivity was present in 18/18 (100%) cases of SFT, which were usually diffuse (4+ in 16 cases, 3+ in 1 case and 1+ in 1 case and intensity was strong in 15 cases, moderate in 2 cases and weak in 1 case). All other tumour types tested were negative for STAT6. CD-34 was done in all cases at initial diagnosis. 16/18 cases (88%) were CD-34 positive. 2 cases (12%) which were CD-34 negative were STAT6 positive. CD-99 and Bcl-2 were positive in most of the cases. CONCLUSION Strong nuclear STAT6 expression is largely specific for SFT and is helpful in distinguishing it from histologic mimics.