Malignant Pleural Effusion Characteristics

Etiology and Pathophysiology

Lung cancer is the most common cause (25-52% of cases), followed by breast cancer (3-27%), lymphomas (12-22%), and other malignancies including ovarian and gastrointestinal cancers 1, 2
In 7-15% of malignant pleural effusions, no primary tumor is identified 3, 2
Pleural metastases typically arise from tumor emboli to the visceral pleural surface with secondary seeding to the parietal pleura 2
Malignant effusions develop through several mechanisms, including disruption or obstruction of lymphatic drainage by tumor cells 3, 2, direct tumor invasion of pleural surfaces 2, hematogenous spread to parietal pleura 2, local inflammatory changes causing increased capillary permeability 2, tumor-induced angiogenesis and vascular invasion leading to hemorrhagic effusions 3, and vascular endothelial growth factor (VEGF) promoting angiogenesis and endothelial permeability 3

Dyspnea is the most common presenting symptom, occurring in more than half of cases 1, 4
Up to 25% of patients are asymptomatic at presentation, with effusions found incidentally 3
Other symptoms include chest pain (particularly in mesothelioma) 1, 4, constitutional symptoms (weight loss, anorexia, and malaise) 1, 4, cough 3, and hemoptysis (suggests underlying lung cancer) 4
Dyspnea results from multiple factors, including reduced chest wall compliance 3, 1, depression of the ipsilateral diaphragm 3, 1, mediastinal shift 3, 1, reduction in lung volume 3, 1, and neurogenic reflexes 3, 1

Most patients present with moderate to large effusions (500-2,000 ml) 4, 5
Malignancy is the most common cause of massive pleural effusions (occupying entire hemithorax), though only 10% present this way 4, 5
Absence of contralateral mediastinal shift in large effusions suggests fixation of the mediastinum 4, 5, mainstem bronchus occlusion by tumor 4, 5, or extensive pleural involvement (as seen in mesothelioma) 4, 5
CT scans help identify small effusions not visible on chest radiographs 4, 5, mediastinal lymph node involvement 4, 5, underlying parenchymal disease 4, 5, and pleural, pulmonary, or distant metastases 4, 5

Typically exudative, though rarely may have transudative characteristics 6
May be serous, hemorrhagic, or chylous (especially in lymphoma) 6
Diagnostic tests should include cytology (positive in 31-55% of cases, lower yield in Hodgkin's disease) 6, 5, cell count and differential 5, total protein 5, lactate dehydrogenase (LDH) 5, glucose 5, pH (low pH correlates with poor prognosis) 6, 5, and amylase 5
High pleural protein values (8-9 g/L) may suggest multiple myeloma 6
Pleural fluid pH and glucose levels correlate with pleurodesis outcome and overall survival 6

Paramalignant effusions are not directly caused by pleural metastases but are related to the primary tumor through mechanisms like postobstructive pneumonia 1, 2, thoracic duct obstruction (chylothorax) 1, 2, pulmonary embolism 1, 2, transudative effusions from atelectasis or low oncotic pressure 1, 2, and treatment-related causes (radiation therapy, chemotherapy drugs) 1, 2
Non-Hodgkin's lymphoma is the most common cause of chylothorax 6

The American Thoracic Society recommends that the diagnosis of Malignant Pleural Effusion (MPE) requires positive cytologic or tissue confirmation of malignant cells to establish the diagnosis definitively, as the presence of malignant cells in the effusion indicates poor prognosis and advanced disease 7
Pleural fluid cytology is positive in 31-60% of cases on first sample, and if the first cytology is negative, it should be repeated a second time, as an additional 27% of cases are diagnosed from the second specimen 8
Pleural biopsy adds approximately 7% diagnostic yield when cytology is negative, and both cell blocks and fluid smears should be prepared for examination 8

Almost all malignant pleural effusions are exudates, though rarely they may have transudative characteristics 9
The presence of malignant cells in pleural fluid indicates poor prognosis with median survival of 3-12 months after diagnosis, and median survival after first thoracentesis is approximately 6-7 months 7

The American Thoracic Society suggests that sediments in pleural effusion confirm an exudative effusion, which accounts for 42-77% of cases being secondary to malignancy 10
The presence of sediment or turbidity in pleural fluid indicates an exudative process, with the sediment containing inflammatory cells, red blood cells, or malignant cells that require cytological analysis, according to the American College of Chest Physicians 10

The American Society of Clinical Oncology recommends therapeutic thoracentesis for symptomatic relief if dyspnea improves with drainage, and pleurodesis with talc for recurrent effusions causing dyspnea, in patients with malignant effusions 10

Pleural fluid cytology yields a diagnostic sensitivity ranging from 49 % to 91 % for detecting adenocarcinoma, with the highest yield obtained when two separate fluid samples are analyzed【11】.

When evaluating malignant pleural or peritoneal effusions, immunohistochemical markers such as CDX‑2, CK20, and CA 19‑9 should be documented to confirm a gastrointestinal (colonic) primary tumor【11】.

A pleural fluid pH ≤ 7.28 is associated with a poor survival prognosis, with median survival reported between 3 and 12 months, and it also predicts a less favorable response to pleurodesis【12】【13】.