Giant-cell tumor in soft parts in a patient with osseous Paget's disease: diagnosis by fine-needle aspiration.

In this report, the cytological features and differential diagnosis of a case of giant-cell tumor (GCT) in soft tissues in a patient with osseous Paget's disease (PD) are described, with histological confirmation. Characteristic cytological findings include a diffuse cellular population of neoplastic cells composed of two types: one group of polygonal or round mononuclear small cells, exhibiting a thin-rim, dense cytoplasm and single hyperchromatic nuclei; and the second group of multinucleated, osteoclast-type giant cells with dozens of round nuclei, showing occasional micronucleoli. A prominent feature is the presence of numerous capillary structures surrounded by tumor cells. The differential diagnosis includes a number of other neoplastic and reactive processes in which giant cells may be abundant. The cytological features of GCT appear to be characteristic enough to allow a suggestive diagnosis. However, the final diagnosis should be made only after the lesion has been studied histologically.