SATB2 immunohistochemistry in osteosarcoma: Utility in diagnosis and differentiation from histologic mimics

Abstract

Background: Diagnostic challenges in osteosarcoma arise in small biopsies with under-representation of the lesion and scant or absent osteoid matrix. Aim: This study aimed to validate the utility of SATB2 antibody in the diagnosis of osteosarcoma and differentiate it from its histological mimics. Materials and Methods: A total of 70 histologically proven cases of osteosarcomas and 97 other histological mimics were included in the study. IHC was performed using SATB2 monoclonal antibody. Results: SATB2 antibody revealed nuclear positivity in all 70 (100%) cases of osteosarcoma. The majority of the conventional osteosarcomas (30 cases, 55.6%) showed 5+ score with a strong-staining intensity. Parosteal osteosarcomas and low-grade central osteosarcoma displayed less extensive staining compared to conventional osteosarcomas. The benign bone-forming tumors (osteoid osteoma and osteoblastoma) showed intense nuclear staining in nearly 100% of the cells. Fibrous dysplasia, osteofibrous dysplasia, callus formation, and myositis ossificans also showed nuclear positivity predominantly along the osteoid. Enchondromas and grade 1 and 2 conventional chondrosarcomas were negative. Positive staining was observed in phosphaturic mesenchymal tumor, juvenile trabecular ossifying fibroma, and desmoplastic fibroma. The other tumors like Ewing sarcoma, lymphoma, chordomas, and undifferentiated sarcomas were negative. Thus, SATB2 can be used to differentiate small-cell osteosarcoma from round-cell sarcomas and enchondroma and chondrosarcomas (grade 1 and 2) from chondroblastic osteosarcoma. Conclusion: It can be used as a useful adjunct in specific settings where osteoid is equivocal.