Pulmonary metastasis of giant cell tumor of the bone diagnosed by fine‐needle aspiration biopsy

Giant cell tumor is a benign but locally aggressive tumor that primarily affects the epiphyses of long bones of young adults. Pulmonary metastases in giant cell tumor are rare (about 1-9%). Here, we report a case of metastatic pulmonary giant cell tumor in a patient who had a previous history of giant cell tumor of the distal femur with multiple recurrences. The diagnosis of pulmonary metastasis was achieved by cytologic evaluation with concurrent immunohistochemical studies in material obtained by fine-needle aspiration biopsy. The aspirate smears contained clustered and dispersed mononuclear and osteoclast-like giant cells that had bland nuclei with inconspicuous nucleoli. All multinucleated cells showed immunoreactivity to KP-1 antibody, a histiocytic marker (not lineage specific) and only a subset of mononuclear cells (30%) stained with this marker. Twenty percent of the mononuclear cells also displayed increased Ki-67 and p53 protein expression. The pulmonary metastasis was similar morphologically and immunophenotypically to the recurrent giant cell tumor of the bone.