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Strong expression of Bcl‐2 in pigmented villonodular synovitis of the knee with aggressive clinical behaviour

Objective: To determine the expression of bcl‐2, p53, and caspase 3, and measure the Ki‐67 proliferation index as well as DNA content and DNA fragmentation in a case of diffuse pigmented villonodular synovitis (PVNS) of the knee with aggressive clinical behaviour. Methods: Expression of p53, Bcl‐2 and Ki‐67 was investigated using immunohistochemistry. In addition, multiparametric flow cytometry was performed for expression of p53, bcl‐2, and caspase 3, as well as analysis of DNA content and distribution of cell cycle phases. DNA fragmentation was detected by the terminal deoxynucleotidyl transferase‐mediated dUTP‐biotin nick end labelling (TUNEL). Results: A strong cytoplasmic positivity for Bcl‐2 protein, a key factor in regulation of apoptosis, was found in the majority of proliferating synovial cells. No apoptotic cell fraction was found by analysis of DNA content. DNA fragmentation was observed in 6.8% of cells. No elevated expression of p53 and caspase 3 was detected. Conclusion: Our results indicate a possible role of dysregulation of apoptosis in this case of PVNS. This aspect in the pathogenesis of PVNS should be clarified in further studies.