Utility of immunohistochemical analysis for cyclo-oxygenase 2 in the differential diagnosis of osteoblastoma and osteosarcoma

Aims: To study the immunoexpression of cyclo- oxygenase ( COX) 2 in osteoblastomas ( OBs) and osteosarcomas ( OSs), and to assess the utility of immunohistochemical analysis for COX 2 in the differential diagnosis of the two tumour forms. Methods: The immunohistochemical features of COX 2 were studied in 11 OBs and 30 OSs, including 26 high- grade OSs ( 16 osteoblastic, 7 chondroblastic, and 3 fibroblastic) and 4 low- grade OSs. Results: Tumour cells from all 11 OBs unequivocally showed diffuse, intense and cytoplasmic immunoreactivity for COX 2. Strong cytoplasmic expression of COX 2 was observed in 5 of 26 ( 19%) high- grade OSs, all chondroblastic. In one osteoblastic- type OS, COX 2 was expressed in the chondroblastic component, but this tumour was considered to be COX 2 negative. No COX 2 expression was noted in atypical osteoblastic cells. Staining in the four low- grade OSs was negative. Conclusion: The results of immunohistochemical analysis of COX 2 suggest that in addition to the routine histopathological evaluation, COX 2 is a valuable diagnostic marker in the distinction between OB and OS.