Histological spectrum of angiofibroma of soft tissue: histological and genetic analysis of 13 cases

Aims Angiofibroma of soft tissue ( AFST ) is a rare soft tissue neoplasm characterized by a fibroblastic cytomorphology and a prominent vascular structure. AFST s possess a novel fusion gene, i.e. NCOA 2 – AHRR / AHRR – NCOA 2 or GTF 2I – NCOA 2 , providing a useful approach to diagnosing AFST . Morphologically, AFST s span a wide spectrum, making diagnosis a challenge. The aim of this study was to review AFST cases and to report previously unknown histological features, which we confirmed by genetic analysis. Methods and results We reviewed 276 cases diagnosed as solitary fibrous tumours/haemangiopericytomas (232 cases), unclassified tumours of fibroblastic differentiation (36 cases), and recently diagnosed AFST s (eight cases), and retrieved 13 cases compatible with AFST . Immunohistochemical staining was performed for these cases, all 13 of which were analysed by reverse transcription polymerase chain reaction and fluorescence in‐situ hybridization. The histological findings were as follows: amianthoid fibres, extravasation of red blood cells, haemosiderin deposition, aggregates of foamy histiocytes, cystic change, necrosis, and haemorrhage. Immunohistochemically, the tumour cells were positive for epithelial membrane antigen (four of 13 cases), desmin (six of 13 cases), CD 163 (13 of 13 cases), CD 68 (seven of 13 cases), oestrogen receptor (13 of 13 cases), progesterone receptor (three of 13 cases), and STAT 6 (one of 13 cases, weak nuclear staining), but they were negative for CD 34, α‐smooth muscle actin, muscle‐specific actin, S100, pan‐cytokeratin, MDM 2, and CDK 4. The AHRR – NCOA 2 fusion gene was detected in eight cases, and NCOA 2 gene rearrangement in nine cases. Conclusion We revealed the previously unreported histological variation and immunohistochemical findings of AFST , and confirmed them by using genetic methods. The results suggested that AFST should be considered in the diagnosis of fibrous or fibrohistiocytic tumours with the above histological features.