HEY1 and synovial sarcoma: Of these, 6 had to be excluded because of later changes in histological classification (3 osteosarcomas, 1 synovial sarcoma with t(X;18), 1 PPM1F-FOXO1 positive surface-sarcoma, 1 mesenchymal chondrosarcoma with HEY1-NCOA2 fusion).