Epithelial Mesothelioma - Clinical Presentation and Diagnosis

Usually, epithelial (or epithelioid) mesothelioma presents itself during the fifth to seventh decades otf life. A significant percentage of patients diagnosed at relatively younger age have experienced asbestos exposure during their childhood.

Symptoms and signs

Symptoms most commonly associated with epithelial pleural mesothelioma include dyspnea and nonpleuritic chest pain. In rare cases, asymptomatic patients experience a unilateral pleural effusion which can be detected during routine chest radiography.

At the time of diagnosis, the most common physical findings range from unilateral dullness to percussion at the lung base, scoliosis towards the side where the malignancy has occurred and palpable chest wall masses.

Paraneoplastic syndromes

There are several different paraneoplastic syndromes associated with epithelioid mesothelioma. Some of these are given below:

Migratory thrombophlebitis
Disseminated intravascular coagulation
Coombs-positive hemolytic anemia
Hypoglycemia
Thrombocytosis
Hypercalcemia linked with discharge of a parathyroid hormone-like peptide

Radiology

In most cases, the malignancy is initially detected on chest radiographs, which usually demonstrate a unilateral pleural abnormality comprising a large, unilateral pleural.

Approximately 60 percent of patients have lesions on the right-side whereas 5 percent of patients are affected by bilateral disease.
On rare occasions, mesothelioma presents itself with a pleural mass or rind or diffuse pleural thickening when pleural effusion is not present.
Only around 20 percent of pleural mesothelioma patients show radiographic signs of asbestosis (for example bibasilar interstitial fibrosis), although majority of patients will have evidence of calcifications and/or pleural plaques.
Occurrence of ipsilateral mediastinal shift is often secondary to encasement of lung by a thick rind of tumor.
Majority of patients experience a significant unilateral loss of lung volume.

Differential Diagnosis

The differential diagnosis includes both benign and malignant processes.

Inflammatory reactions, for instance chronic organized empyema, can often be similar to the dense parietal and visceral pleural thickening as well as a large pleural effusion which is characteristic of mesothelioma.
Epithelial mesothelioma can be exceptionally difficult to differentiate grossly and histologically from metastatic involvement of the pleura. Potential primary sources include breast, lung, kidney, stomach, thymus, ovary, and prostate.
Sarcoma (for example fibrosarcoma) and malignant fibrous histiocytoma can present itself in the same manner and infiltrate like sarcomatous mesotheliomas.
The mixed-cellular form of mesothelioma can histologically bear a resemblance to sarcomatoid carcinoma and synovial sarcoma.

Diagnosis of Epithelial (Epithelioid) Mesothelioma

In many cases, malignant epithelioid mesothelioma is misdiagnosed initially and patients may have to undergo multiple consultations and tests before a correct diagnosis can be achieved. A correct diagnosis is essential for selecting appropriate treatment, and also for maintaining proper epidemiologic records and dealing with any eventualities of subsequent litigation.

While thoracentesis or closed pleural biopsy can usually help confirm the diagnosis of pleural malignancy, enough tissue may not be obtained to make a differentiation between mesothelioma and lung adenocarcinoma. Moreover, negative results do not imply the absence of mesothelioma. Although used rarely, surgical procedures (via open thoracotomy or video thoracoscopic biopsy) have shown to provide higher diagnostic yield.

The challenges faced while confirming a diagnosis of mesothelioma have been illustrated through a study involving 188 successive patients examined between 1973 and 1990. In 98 percent of cases, diagnosis was established using video-assisted thoracoscopic (VATS) biopsy, in comparison to 39 percent for closed pleural biopsy and fluid cytology combined and 26 for thoracentesis alone. The VATS procedures were performed using local anesthesia in an endoscopy suite and had minimal complications or morbidity.

Around 10% of patients who go through diagnostic procedures for mesothelioma end up seeding the biopsy site with tumor cells which later leads to recurrance in the chest wall. Radiation therapy is often used for the treatment of patients diagnosed with symptomatic, recurrent disease occurring at the site of biopsy. Such complications can be avoided if prophylactic radiation therapy is administered to the surgical scar or thoracentesis site.

Performing a concurrent bronchoscopy may be vital for making a differentiation between mesothelioma and metastatic adenocarcinoma of the lung, since endobronchial lesions are seldom seen in mesothelioma.

A new approach to differentiate between mesothelioma and adenocarcinoma of the lung is currently under development. This new approach relies on gene expression profiling, by identifying specific genes that are expressed in malignant mesothelioma but not in case of adenocarcinoma or normal lung tissue.

Tumor markers

A diagnostic role for serum tumor markers is yet to be established. Biomarkers that have shown plenty of potential in recent times include osteopontin and mesothelin.

Osteopontin

A glycoprotein, osteopontin mediates cell-matrix interactions and is overexpressed in several different forms of cancer. In a study involving 190 patients, it was noticed that osteopontin levels were higher among patients with malignant epithelial mesothelioma (133 ng/mL) in comparison to patients diagnosed with asbestos-related nonmalignant pleural disease (30 ng/mL) or those with no prior history of asbestos exposure (20 ng/mL). Pleural fluid osteopontin levels can also be useful in identifying malignant mesothelioma. In a single study at least, it was noticed that osteopontin had a lower diagnostic accuracy as compared to mesothelin among individuals suspected to have malignant epithelioid mesothelioma.

Mesothelin

A glycoprotein, mesothelin is expressed on the surface of normal mesothelial cells. These are highly overexpressed in case of epithelial mesothelioma. It is believed that soluble mesothelin-related peptides (SMRPs) are either cleaved peptide fragments of mesothelin, or abnormal forms of mesothelin which are not able to bind to membranes and are present in the serum.

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