Special AT-rich sequence-binding protein 2 immunohistochemistry in the diagnosis of osteosarcoma in dogs.

Malignant osteoblasts can have markedly pleomorphic phenotypes and variable amounts of tumour-associated matrix, complicating the ability of pathologists to accurately differentiate osteosarcoma (OSA) from other types of neoplasms using only histopathology. Current immunohistochemical markers for animals have limited sensitivity and specificity in identifying OSA or produce inconsistent results. Immunohistochemistry (IHC) for special AT-rich sequence-binding protein 2 (SATB2) has been used in human medicine to aid in identification of normal and neoplastic osteoblasts, and the objective of this study was to determine whether this marker could also be useful for the diagnosis of canine OSA. Initially, SATB2 IHC was performed on eight samples from cases of well-differentiated canine OSA and on other tumour types for which OSA is a differential diagnosis, as well as on normal tissues, to assess sensitivity and cross-reactivity. Following confirmation that SATB2 is immunoreactive for normal and neoplastic canine osteoblasts and negative in other non-osseous mesenchymal cell types and organs, SATB2 IHC was tested on 123 cases of poorly differentiated malignant neoplasms as part of a panel with other immunohistochemical markers, as appropriate, based on histomorphology and differential diagnoses. The conclusion is that SATB2 IHC is a sensitive and specific marker for identifying canine OSA when used in a panel with other immunohistochemical markers and in conjunction with supportive clinical history.