CIC-DUX4 and BCOR-CCNB3 fusion-gene-associated small round cell sarcomas account for a proportion of pediatric small round cell sarcomas, but their pathological features have not been sufficiently clarified. We reviewed a large number of soft tissue tumors registered at our institution, retrieved the cases of unclassified tumors with a small round cell component, and subjected them to histopathological, immunohistochemical, and gene profile analysis. We reviewed 164 cases of unclassified tumors with a small round cell component and analyzed them by RT-PCR and FISH. Tumors positive for a specific fusion-gene were also subjected to histopathological and immunohistochemical examinations. We identified 16 cases of BCOR-CCNB3/CIC-associated (CIC-DUX4 or CIC gene rearrangement-positive) sarcomas. These included seven BCOR-CCNB3 sarcomas and nine CIC-associated sarcomas. Heterogeneous elements included a myxoid spindle cell component in three BCOR-CCNB3 sarcomas and an epithelioid cell component in two CIC-associated sarcomas (one CIC-DUX4-positive and one CIC-DUX4-negative sarcomas). Mitotic activity was low in both heterogeneous components. By immunohistochemistry, in seven BCOR-CCNB3 sarcomas expression of EMA was positive in two cases, of p63 in three, of CD56 in six, of TLE1 in seven, of NKX2.2 in two, of CCNB3 in seven, and of BCOR in six cases (one case could not be tested for BCOR). In nine cases of CIC-associated sarcoma, CD56 was expressed in five, alpha-smooth muscle actin in one, ERG in three, and CD99, WT1 and TLE1 each in eight cases. Both sarcoma types showed not only a small round cell component, but also a myxoid/epithelioid component with low mitotic activity.

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Aims: Angiofibroma of soft tissue (AFST) is a rare soft tissue neoplasm characterized by a fibroblastic cytomorphology and a prominent vascular structure. AFSTs possess a novel fusion gene, i.e. NCOA2-AHRR/ AHRR-NCOA2 or GTF2I-NCOA2, providing a useful approach to diagnosing AFST. Morphologically, AFSTs 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 AFSTs (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), CD163 (13 of 13 cases), CD68 (seven of 13 cases), oestrogen receptor (13 of 13 cases), progesterone receptor (three of 13 cases), and STAT6 (one of 13 cases, weak nuclear staining), but they were negative for CD34, a-smooth muscle actin, , S100, pan-cytokeratin, MDM2, and CDK4. The AHRR-NCOA2 fusion gene was detected in eight cases, and NCOA2 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.

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PPB associated with HB is characterized by high incidence, late onset and recurrent bleeding, resulting in long hospitalization.