SATB2 is a novel marker of osteoblastic differentiation in bone and soft tissue tumours

Aims Diagnosing osteosarcoma can be challenging, as osteoid deposition is often limited in extent, and hyalinized stroma may closely mimic osteoid. SATB2 is a nuclear protein that plays a critical role in osteoblast lineage commitment. The aim of this study was to examine SATB2 expression in osteosarcomas and other bone and soft tissue tumours, to evaluate its diagnostic utility. Methods and results Whole sections of 215 tumours were evaluated, including 52 osteosarcomas (43 of skeletal origin; nine extraskeletal), 86 other bone tumours, and 77 other soft tissue tumours. All skeletal osteosarcomas, osteoblastomas, osteoid osteomas, and fibrous dysplasias, eight (89%) extraskeletal osteosarcomas, five (83%) giant cell tumours and three (50%) chondromyxoid fibromas showed nuclear immunoreactivity for SATB2. Staining in other bone and soft tissue tumours was predominantly limited to areas of heterologous osteoblastic differentiation. Focal weak staining was identified in one (9%) unclassified pleomorphic sarcoma and one (13%) monophasic synovial sarcoma. SATB2 was negative in all soft tissue tumours with prominent sclerotic stromal collagen. Conclusions SATB2 is a marker of osteoblastic differentiation in benign and malignant mesenchymal tumours. Although SATB2 is not specific for osteosarcoma, it has the potential to be a useful adjunct in some settings, particularly in the distinction between hyalinized collagen and osteoid.