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

Our plain-English summary of Pseudomesotheliomatous Adenocarcinoma Presenting as Hemothorax and Mimicking Mesothelioma: A Case Study, by M. Ijim, S. Keddabi, C. Rachid, et al (Curēus, 2026).

The study

• Authors: M. Ijim, S. Keddabi, C. Rachid, O. Fikri, L. Amro
• Journal: Curēus
• Published: 2026;18(4):e106699
• Type of article: Case report
• Read it: PubMed · Publisher · Free full text

Abstract

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.

Copyright © 2026, IJIM et al.

In plain English

This was a case report of one patient: a 53-year-old Moroccan man, a chronic smoker (30 pack-years) with prolonged exposure to wood smoke and poultry/livestock droppings. The authors reported no known asbestos exposure. The patient had chest pain, breathlessness and cough, and tests showed bleeding into the left chest cavity (hemothorax). A chest tube drained 2400 mL of bloody fluid. A CT scan showed nodular thickening of the pleura (the lung lining) up to 19.5 mm. A bone scan showed a single secondary bone lesion (cancer spread to bone) in the D2 vertebral body. The early findings, including the biopsy appearance and raised hyaluronic acid in the pleural fluid, were suggestive of mesothelioma. However, immunohistochemistry stains were negative for mesothelial markers and positive for the lung markers TTF-1 and Napsin A. This gave a diagnosis of pseudomesotheliomatous lung adenocarcinoma, a lung cancer that mimics mesothelioma. The patient received cisplatin and vinorelbine and died suddenly after two cycles. The authors concluded that mesothelioma cannot be diagnosed without formal histological evidence, and that immunohistochemistry plays a crucial role.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: case report (single patient)
• Who was studied: One 53-year-old Moroccan man, a chronic smoker (30 pack-years, stopped 20 days before), with chronic dyspnea and bronchitis, seen in a pulmonology department in Marrakech
• Exposure: Smoking and prolonged exposure to wood smoke and poultry/livestock droppings; the authors state the patient had no known exposure to asbestos
• Main results:
  • Hematocrit measured in both pleural fluid and blood confirmed hemothorax. Table 1 gives pleural hematocrit 29.5%, serum hematocrit 34.3%, and a ratio of 86%.
  • A chest tube drained a total of 2400 mL of bloody pleural fluid from the patient
  • Chest CT showed nodular pleural thickening up to 19.5 mm, a large loculated left collection (19.8 cm), mediastinal lymph node enlargement and emphysema, with no soft tissue or bone invasion
  • Bone scan showed a single secondary (spread) bone lesion in the D2 vertebral body
  • The nodular pleural thickening, the mesothelial-like appearance on biopsy and the elevated hyaluronic acid were suggestive of mesothelioma
  • Immunohistochemistry: mesothelial markers (calretinin, CK5/6, WT1, GATA3) were negative. TTF1 was strongly positive and Napsin A moderately positive, supporting pseudomesotheliomatous lung adenocarcinoma.
  • No oncogenic driver mutations were found, and PD-L1 expression was negative (Tumor Proportion Score 0%)
  • The patient was treated with cisplatin and vinorelbine and died suddenly after two cycles
• The authors' conclusion: The authors concluded that the absence of a visible lung mass does not confirm a primary pleural origin, that mesothelioma cannot be diagnosed without formal histological evidence, and that immunohistochemistry plays a crucial role

Topics

Medical terms in this study, explained in our Lexicon: Pseudomesotheliomatous Adenocarcinoma, Hemothorax, Mesothelioma, Lung Adenocarcinoma, Pleural Mesothelioma, Pleural Thickening, Pleural Effusion, Thyroid Transcription Factor-1 (TTF-1).

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