Two Cases of Suspected Diffuse Mesothelioma in Which a Definitive Diagnosis Was Difficult to Make from the Initial Pleural Biopsy Findings

Background. Pleural biopsy by video-assisted thoracoscopic surgery (VATS) is the most commonly performed diagnostic procedure for diffuse mesothelioma. We encountered 2 cases of suspected diffuse mesothelioma in which a definitive diagnosis was difficult to make based on the initial VATS pleural biopsy findings. Cases. The first case was a 74-year-old man with dyspnea. Pleural fluid cytology was malignant, thus suggesting diffuse mesothelioma. Computed tomography (CT) did not show either pleural thickening or any mass lesions. On VATS biopsy, the histological diagnosis was atypical mesothelial proliferation because the atypical cells did not infiltrate the adipose tissue, and the molecular pathological markers were negative. During follow-up, CT showed pleural thickening and mediastinal lymph node swelling. We started immunotherapy 2 years after the biopsy. The second case was a 71-year-old man with dyspnea. CT showed right pleural effusion with extensive pleural plaques and thickening. On VATS biopsy, the histological diagnosis was also atypical mesothelial proliferation. Although challenging, pleural decortication was performed because diffuse mesothelioma was strongly suspected. The pathology results confirmed epithelioid mesothelioma. Conclusion. These cases were difficult to diagnose based on the findings of the initial VATS pleural biopsy. When diffuse mesothelioma is strongly suspected and there is evidence of disease progression, we should either perform a repeat biopsy or start treatment for mesothelioma.