Immunohistochemical detection of STAT6, CD34, CD99 and BCL-2 for diagnosing solitary fibrous tumors/hemangiopericytomas.

Solitary fibrous tumors (SFTs)/hemangiopericytomas (HPCs) are uncommon mesenchymal neoplasms of fibroblastic type that can arise anywhere in the body. Recently, NGFI-A binding protein 2 (NAB2)-signal transducer and the activator of transcription 6 (STAT6) fusion gene were discovered as a hallmark of SFTs/HPCs by using whole-exome, and transcriptome sequencing; consequently, the fusion gene can be rapidly detected by STAT6 immunohistochemistry. In this study, 53 formalin-fixed, paraffin-embedded (FFPE) tissues were performed using immunohistochemistry with antibodies against STAT6, CD34, CD99 and Bcl-2. Nuclear STAT6 positive staining was present in 51 cases (51/53, sensitivity 96.2%), which were usually diffuse (4+ in 14 cases; 3+ in 13 cases; 2+ in 9 cases; 1+ in 15 cases) and intense (strong in 17 cases; moderate in 22 cases; and weak in 12 cases) staining. CD34 was positive in 47 cases (47/53, sensitivity 88.7%), CD99 was positive in 50 cases (50/53, sensitivity 94.3%) and Bcl-2 was positive in 51 cases (51/53, sensitivity 96.2%). There is no difference among categories such as age, sex, location, tumor size, or estimated dignity in immunohistochemical staining of STAT6, CD34, CD99 and Bcl-2. The nuclear STAT6 being positive is a helpful and highly sensitive marker in diagnosis of SFTs/HPCs. Considering immunohistochemical STAT6, CD34, CD99 and Bcl-2 findings together can provide more supportive diagnostic information.