Pseudomesotheliomatous Carcinoma of the Lung with Morphological Characteristics of Signet Ring Cell Carcinoma: An Autopsy Case Report

A 50-year-old woman presented with left pleural effusion. A pleural fluid cell-block specimen and longitudinal lymph node needle biopsy suggested signet ring cell carcinoma (SRCC). Although computed tomography showed a consolidation shadow in the left lower lobe, a left lung biopsy could not be performed. Upper gastrointestinal endoscopy revealed no malignancies. We administered carboplatin, pemetrexed, ipilimumab, and nivolumab for lung cancer; however, she died due to progressive respiratory failure. Pathological autopsy revealed that the left pleura was thickened as in mesothelioma, based on which pseudomesotheliomatous carcinoma of the lung (PMCL) was diagnosed. PMCLs exhibiting an SRCC morphology are rare.