Pseudomesotheliomatous Adenocarcinoma Presenting as Hemothorax and Mimicking Mesothelioma: A Case Study.

Pseudomesotheliomatous carcinoma of the lung (PCL) is a rare and aggressive subtype of peripheral lung adenocarcinoma characterized by diffuse pleural involvement, clinically and radiologically mimicking malignant pleural mesothelioma. We report the case of a 53-year-old Moroccan man presenting with hemothorax, a rare initial manifestation of PCL. Radiological imaging revealed nodular pleural thickening with loculated pleural effusion, while histopathological and immunohistochemical analyses confirmed pseudomesotheliomatous lung adenocarcinoma, distinguished by positive epithelial markers (TTF-1, Napsin A) and negative mesothelial markers. Despite initial management with chest drainage and systemic chemotherapy, the prognosis remained poor, consistent with the aggressive nature of this disease. This case highlights the diagnostic challenge posed by PCL due to its clinical and radiological resemblance to mesothelioma and underscores the essential role of immunohistochemistry in establishing an accurate diagnosis. Increased awareness of this entity is critical for appropriate patient management and guiding future therapeutic strategies.