[Giant cell-rich lesions of bone and their differential diagnosis].

Giant cell-rich lesions form a heterogeneous group of reactive and truly neoplastic processes with diverse clinical presentation and biological behavior. Common to all of them are variably numerous multinucleated osteoclast-like giant cells and the presence of mononuclear stroma. Based on the histological picture alone it is sometimes impossible to reliably distinguish certain tumors from each other. The pathologist has to know the patient´s age, the exact localization, tumor growth dynamics and its radiographic characteristics. Secondary reactive changes occur frequently and these can completely alter the morphology of the lesion and thus overshadow the underlying neoplasm. Reparative changes in a pathological fracture may histologically mimic primary bone malignancy. Immunohistochemistry helps only in select cases and molecular genetic methods still have very limited utility for the diagnosis of giant cell-rich tumors. It is necessary to correlate the microscopic features of the lesion with clinical and radiological findings. A correct diagnosis is of paramount importance for proper treatment and prognosis.