SPECIAL SELECTED TOPICS- RESPIRATORY SYSTEM DISORDERS-SSTRSDO-QAA 024

1. What are the most frequent pleural tumors?

Pleural tumors may be primary or secondary. Metastatic involvement of the pleura from lung, breast, ovarian, or gastrointestinal cancers is far more common than primary pleural tumors. Malignant mesothelioma is the most important primary malignant pleural tumor and is strongly associated with asbestos exposure.

Solitary fibrous tumor is the most common benign primary pleural neoplasm. Pleural metastases often produce malignant pleural effusion. Patients commonly present with chest pain, dyspnea, cough, and pleural effusion. Imaging studies demonstrate pleural thickening or nodular masses.

Histopathology and immunohistochemistry establish the diagnosis. Prognosis depends on the tumor type and extent of disease.

2. Which etiologic agents are associated with malignant mesothelioma?

Malignant mesothelioma is strongly associated with occupational exposure to asbestos fibers, particularly amphibole asbestos such as crocidolite. The disease typically develops after a long latent period of 20–50 years following exposure.

Workers in shipbuilding, construction, insulation, and asbestos manufacturing are at highest risk. Unlike bronchogenic carcinoma, smoking does not significantly increase the risk of mesothelioma. Chronic asbestos exposure causes repeated mesothelial injury, inflammation, and genetic mutations.

Germline or somatic alterations involving the BAP1 tumor suppressor gene have been identified in many patients. The tumor most commonly involves the pleura but may also affect the peritoneum.

Strict occupational safety measures have reduced its incidence in many countries. Prognosis remains poor despite modern treatment.

3. What are the morphologic characteristics of malignant mesothelioma?

Malignant mesothelioma usually presents as diffuse nodular thickening of the pleura that progressively encases the lung like a rigid shell. The pleural surface becomes gray-white, firm, and irregular. The tumor invades the chest wall, diaphragm, pericardium, and adjacent lung tissue.

Microscopically, three major patterns are recognized: epithelioid, sarcomatoid, and biphasic (mixed). The epithelioid type forms tubules, papillae, or sheets of polygonal cells. The sarcomatoid type consists of spindle-shaped malignant cells resembling fibrosarcoma.

Immunohistochemistry helps distinguish mesothelioma from metastatic adenocarcinoma. Extensive pleural fibrosis and recurrent hemorrhagic effusions are common. Local invasion predominates, although distant metastases may occur in advanced disease.

4. What is the clinical course of disease in patients with malignant mesothelioma?

Malignant mesothelioma has an insidious onset and an aggressive clinical course. Patients usually present with progressive dyspnea, persistent chest pain, dry cough, fatigue, and weight loss. Recurrent pleural effusions are common and often hemorrhagic. As the tumor enlarges, it encases the lung, causing severe restriction of lung expansion and respiratory impairment. Local invasion into the chest wall produces persistent pain.

Diagnosis is established by imaging, thoracoscopy, biopsy, and immunohistochemical studies. Most patients present with advanced disease because early symptoms are nonspecific.

Treatment includes surgery in selected patients, chemotherapy, immunotherapy, and palliative care. Despite advances in management, the overall prognosis remains poor, with a median survival of approximately 12–18 months after diagnosis.      

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DR.C.GANESAN M.D

PROFESSOR OF MEDICINE