Chest computed tomography (CT) revealed a focal ground glass opacity (GGO) with a minimal solid area in a 75‑year‑old man. The shadow was located in the periphery of the right upper lobe and measured 11 mm in diameter. The patient had a medical history of metachronous prostate and gastric cancers. The patient had been treated with androgen deprivation therapy for prostate cancer for 12 years and underwent subtotal gastrectomy for triple gastric cancers 7 months before. Since primary lung adenocarcinoma was suspected, CT‑assisted percutaneous needle biopsy was performed. Histology revealed the sheet‑like and trabecular proliferation of atypical cells, suggesting that the lesion was moderately to poorly differentiated adenocarcinoma. Adenocarcinoma cells showed subepithelial extension causing the thickening of alveolar walls. A tumor thrombus was not detected in the blood or lymphatic vessels. Immunohistochemistry revealed that carcinoma cells were negative for cytokeratin 7 (CK7), CK20, thyroid transcription factor‑1 and CDX2 and positive for prostate‑specific antigen and P504S. Based on these findings, the patient was diagnosed with metastatic carcinoma from prostate cancer. The disease remained stable for 4 months after the diagnosis, and no new lesions were observed on chest CT. Metastatic carcinoma rarely presents with focal GGO. Lung biopsy is necessary to identify the pathology of the lesion, and the primary site needs to be confirmed by immunohistochemistry with specific markers, particularly in a case of metachronous multiple cancers. A tumor thrombus, which is suggestive of lymphangitic carcinomatosis or pulmonary tumor thrombotic microangiopathy, also needs to be evaluated.

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