OSTEOCALCIN AND OSTEONECTIN IMMUNOREACTIVITY IN THE DIAGNOSIS OF OSTEOSARCOMA

Osteosarcomas (OSAs) can be difficult to distinguish histologically fr om tumors with significantly different biologic potentials and treatme nt protocols. The correct diagnosis of OSA relies on identification of malignant osteoblasts that are capable of producing neoplastic bone. To determine the use of immunohistochemistry for the diagnosis of OSA, 106 tumors from the Massachusetts General Hospital and the University of Vermont were immunostained with monoclonal antiosteocalcin (OC) an d antiosteonectin (ON) antibodies. They included 42 OSAs, 25 non-bone- forming sarcomas, 24 other malignant tumors including lymphomas, carci nomas, and melanomas, and 15 benign bone tumors. Cytoplasmic staining with OC showed 70% sensitivity and 100% specificity, while staining wi th ON showed 90% sensitivity and 54% specificity for bone-forming tumo rs, consistently staining cell types other than osteoblasts. Of the OS As, 83% demonstrated matrix staining with one or both antibodies, wher eas dense collagen was negative for both antibodies in all tumors. We conclude that tumor cell cytoplasmic staining with monoclonal OC may b e helpful in distinguishing OSAs from other malignancies, and staining of extracellular matrix for OC and ON antibodies concurrently may hel p distinguish bone matrix from dense collagen.