Tumors harboring osteoclast-like giant cells (OGCs) at extraosseous site are extremely rare. These rare tumors have been detected most frequently in the pancreas and few pulmonary tumors harboring OGCs have been previously reported. In addition, the genetic profiles of these tumors have remained virtually unknown. Therefore, we report a case of pulmonary adenocarcinoma harboring OGCs in which k-ras mutation and immunohistochemical study of proteins associated with OGCs were examined. The case was a 70-year-old man, who demonstrated a pulmonary mass associated with unusual radiological features. Histopathologically, three different cell types, mucinous adenocarcinoma cell, OGC and mononuclear cell were detected. OGCs were immunohistochemically negative for epithelial markers and positive for histiocytic markers but mononuclear cells were immunopositive for epithelial markers. In addition, both mononuclear and adenocarcinoma cells had the same k-ras mutation profiles and mononuclear cells were immunohistochemically positive for macrophage colony-stimulating factor (M-CSF), one of the factors associated with OGC differentiation. Therefore, mononuclear cells were considered to be derived from neoplastic epithelium and OGCs could represent non-neoplastic cells. In addition, M-CSF locally produced could promote the differentiation of OGCs.
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