The utility of SATB2 immunohistochemical expression in distinguishing between osteosarcomas and their malignant bone tumor mimickers, such as Ewing sarcomas and chondrosarcomas.

SATB2 is commonly expressed in osteosarcomas. Although apparently being a valuable diagnostic marker for differentiating between small cell osteosarcoma (SCO) and other small round cell tumors of bone, for instance Ewing sarcoma family of tumors (ESFT), it has not been tested in a large series of ESFT and chondrosarcomas so far. We studied the immunohistochemical expression of SATB2 in 42 osteosarcomas, 31 chondrosarcomas, and 371 genetically confirmed ESFT. SATB2 positivity was detected in 90.4% of osteosarcomas, 87.5% of SCO, 91.3% of osteoblastic osteosarcomas, and in all chondroblastic and parosteal osteosarcomas. The osteoblastic and SCO subtypes expressed SATB2 more intensely than other histological types. SATB2 was expressed in 46.6% of chondrosarcomas, and in 1.3% of ESFT. Sensitivity and specificity of SATB2 immunoexpression were 90.4% and 95.3%, respectively. The positive and negative predictive values in osteosarcoma diagnosis were 66.6% and 98.9%, respectively. In chondrosarcoma, SATB2 immunoexpression was more frequent and intense in high-grade chondrosarcoma (Grade III) and uncommon in chondrosarcoma grade I. SATB2 positivity was detected in 55.6% of chondrosarcomas grade II. SATB2 apparently cannot distinguish between chondroblastic osteosarcoma and high-grade chondrosarcoma. Nevertheless, SATB2 is frequently expressed in osteogenic tumors, but is rarely positive in ESFT, and with the support of CD99 expression and specific molecular studies, it is very useful for distinguishing between these two lesions. Although SATB2 immunoexpression helps to distinguish osteosarcoma from their mimickers, the identification of malignant osteoid matrix formation and the integration of clinical and radiological data remain the corner stone of osteosarcoma diagnosis and as yet no antibody has equalled the diagnostic value of this important morphologic hallmark.