Numerous osteoclast-like giant cells in metastases from lung adenocarcinoma, but absent from primary tumor

We report a rare case of lung adenocarcinoma in a 54-year-old man, in whom osteoclast-like giant cells (OCGCs) were found only in metastases. Autopsy revealed that metastases involving the tongue, gallbladder, stomach, intestines, right adrenal gland, and bones contained numerous OCGCs. Some metastases to the lungs and liver also contained OCGCs, but the primary tumor and metastases to the right atrium, spleen, left adrenal gland, and lymph nodes did not. Primary lung carcinoma cells were positive for cytokeratin 7 (CK7), epithelial membrane antigen (EMA), thyroid transcription factor 1 (TTF-1), and Napsin A, but were negative for vimentin and CD68. Frequently poorly cohesive metastatic carcinoma cells admixtured with OCGCs showed weak CK7/EMA positivity, no TTF-1/Napsin A staining, and newly expressed vimentin. OCGCs were positive only for CD68 and vimentin, implying reactive cells. OCGCs can develop only in metastatic lesions, possibly associated with their anaplastic changes or epithelial mesenchymal transition.