Mesothelioma Overview

Mesothelioma

 

Overview

Mesothelioma is a type of cancer that occurs in the mesothelium, or the thin membrane lining the body's internal organs. The most common site of mesothelioma is within the pleura, a thin membrane which surrounds the lungs and chest wall. Mesothelioma also occurs in the peritoneum, which surrounds the abdominal cavity, as well as within the pericardium, which envelops the heart.¹

Mesothelioma is associated with asbestos exposure. Most individuals diagnosed with mesothelioma have worked with or within proximity of airborne asbestos particles or asbestos dust. Asbestos is a naturally occurring mineral that has been used as an insulation material dating back to the early Greco-Roman eras. Industrial use of the mineral, however, is the culprit for the majority of exposures. While symptoms are similar, mesothelioma is not lung cancer and there is no known nexus between smoking and the development of mesothelioma.²

Symptoms and Warning Signs

There is a great deal of latency between exposure to asbestos and the onset of mesothelioma symptoms. In many patients, first signs of the disease will not occur for 30 to 50 years after exposure.³ Pleural mesothelioma, which is the most common form of the disease, is associated with the following symptoms:

• Pain within the chest wall
• Shortness of breath (due to the accumulation of fluid in the pleural space, also known as pleural effusion)
• Excessive fatigue
• Chronic cough
• Blood in the respiratory tract fluid (sputum)

Symptoms of abdominal disease, like peritoneal mesothelioma, will not typically manifest until the cancer is in its later stages. These symptoms include abdominal pain, buildup of fluid in the peritoneal space, a visible mass in the abdominal region, and problems with bowel function. Symptoms of pericardial mesothelioma include chest pain, heart palpitations, and shortness of breath. Symptoms of later-stage or metastasized disease include extreme pleural effusion, blood clotting, diminished blood sugar levels, and severe fluid build-up in the peritoneal space.⁴

Diagnosis of Mesothelioma

Physicians have difficulty conclusively diagnosing mesothelioma in the early stages of their evaluation because the symptoms of the disease so closely mimic those of other malignancies and illnesses, such as lung cancer. In most cases the first step is a thorough physical exam and review of a patient's medical history. If a patient has a known asbestos-exposure history, suspicion of mesothelioma will likely be enhanced.⁵

Imaging

A chest X-ray will likely be used to determine if there is visible growth in the pleural, pericardial, or peritoneal space. These early-stage imaging exams can reveal a thickening in the pleural space, which is common among those who worked with asbestos. A magnetic resonance image (MRI) or computer topography (CT) scan is then performed, which can indicate the buildup of fluid in the pleural space or elsewhere. If there is a substantial fluid buildup, a cytological exam will likely be necessary to examine the fluid. A pleural tap or chest drain procedure is then used to extract fluid.

Biopsy

If cytology confirms the presence of malignant cells, a biopsy will likely be used to examine surrounding tissue for the presence of malignant growth. Depending on where the cancer occurs, biopsy procedures will differ. A thoracoscopy will likely be used to examine malignant cells in the chest, while a laparoscopy would be used to extract cells from the abdominal region.⁶

Screening: Asbestos Risk and Assessment

There has yet to be developed a universal method of screening those who are believed to be at high risk of mesothelioma, which are those people who have known asbestos exposure history. As mesothelioma is often not diagnosed until it is in its later stages, physicians are working on methods of identifying early-stage diagnosis or risk assessment platforms. Early diagnosis of the disease dramatically improves prognosis and expands a patient's treatment options.⁷ Chemically, there is no conclusive test for early stage mesothelioma, though identifying serum osteopontin and mesothelin-related protein levels has shown potential to be the first identified chemical indicators of mesothelioma.⁸

Pathophysiology

The relationship between pleural mesothelioma and asbestos exposure is clearer than the relationship between asbestos and pericardial mesothelioma and peritoneal mesothelioma. Asbestos has six different varieties. Amphibole asbestos fibers are those which are more commonly associated with asbestos exposure. Amphibole fibers are microscopic with a long, thin composition. Inhaled asbestos fibers will lodge within the outer portion of the lung, eventually penetrating the visceral surface lining of the mesothelium and potentially forming a malignancy. Physicians surmise, though have not confirmed, that peritoneal mesothelioma is caused by ingested asbestos fibers which penetrate the abdominal cavity's mesothelial lining through contaminated sputum. In addition, there is a common belief among physicians and cancer researchers that peritoneal mesothelioma may be caused by asbestos fibers transported through the lymphatic system.

Some of the most current theories concerning the pathogenesis of the disease are now centered around the genetic mutations of patient DNA. Cell membranes can envelop microscopic fibers, which may react with chromosomal structures.

Over time, asbestos fibers within the mesothelium cause a sustained inflammation of the surrounding tissue. Fibers will collide with and irritate mesothelial cells, causing the development of scar tissue and malignant plaques on the surface of the membrane.⁹