A Case of Pseudo-lung Carcinomatous Mesothelioma with Radiographic Images and Multiple Distant Metastases, as Seen in Typical Primary Lung Cancer, Diagnosed by Bronchoscopy

<p>Background. Malignant pleural mesothelioma (MPM) is a malignant tumor arising from the pleura. It is sometimes difficult to differentiate from primary lung cancer, which originates in the lung parenchyma. Case. A 67-year-old man visited a primary physician with the chief complaint of exertional dyspnea. Chest computed tomography (CT) showed a huge mass in the right upper lobe of the lung and a nodule suggestive of pleural dissemination. The patient was referred to our department for an initial examination. Fluorodeoxyglucose-positron emission tomography (¹⁸FDG-PET) -CT revealed multiple metastases to the lymph nodes, bones, and bilateral adrenal glands. Primary lung cancer arising from the right upper lobe was initially suspected and a bronchoscopy examination was performed. However, a transbronchial biopsy (TBB) of an invasive tumor on the mucosa of the right B³a bronchus resulted in a definitive histological diagnosis of malignant mesothelioma (epithelial type), contrary to radiographic imaging. The patient was diagnosed with stage IV MPM (cT4N2M1). Nivolumab plus ipilimumab was given as the first-line therapy, and CT showed a partial response after two courses. However, the disease progressed owing to peritoneal dissemination during the 3rd course. Conclusion. There are few reports of cases where a TBB has been able to be used to diagnose malignant mesothelioma. We herein report a case of pseudo-lung carcinomatous mesothelioma with radiographic images that could be mistaken for typical primary lung cancer with multiple distant metastases.</p>