X-chromosome inactivation in patients who have pigmented villonodular synovitis.

We performed a histological examination and DNA analysis on samples of tissue from a forty-seven-year-old woman who had a clinical diagnosis of pigmented villonodular synovitis. The histological examination confirmed the diagnosis. The evaluation of the samples of tissue with preferential X-chromosome inactivation analysis (a molecular biological method for the study of clonality in tumors) showed that the lesion was polyclonal in origin. We concluded, therefore, that pigmented villonodular synovitis is more likely to be a reactive process than a true neoplasm.