Mesothelial cells are a layer of specialized cells that line the body cavities, including the pleura (lining of the lung), peritoneum (lining of the abdominal cavity), and pericardium (lining of the heart). The tissue formed by these cells is called mesothelium.
The mesothelium contains both an outer and an inner layer. The inner layer surrounds the organs themselves, while the outer layer lines the body cavities in which the organs covered by mesothelial cells reside. The mesothelial cells themselves produce and secrete a small amount of lubricating fluid between the two layers that permit the organs to move smoothly against adjacent organs and structures.
Like other cells of the body, mesothelial cells can also grow abnormally, leading to the development of tumors. The tumors of the mesothelial cells can be benign (noncancerous) or malignant (cancerous). A malignant tumor of the mesothelium is called malignant mesothelioma. Because most mesothelial tumors are cancerous, malignant mesothelioma is often simply referred to as mesothelioma. This article focuses on mesothelioma of the lining of the lungs (pleural mesothelioma), which is the most common form of all mesotheliomas.
Mesothelioma is an uncommon disease. The disease is more common in men of Caucasian and Hispanic ethnicity, and less common among Asian and African American men. The disease shows a male predominance, which is due to occupational exposure.
The main risk factor for developing pleural mesothelioma is asbestos exposure. Asbestos is a mineral that occurs naturally as strong, flexible fibers that can be separated into thin threads and woven. Asbestos has been widely used in many industrial products, including cement, brake linings, roof shingles, flooring products, textiles, and insulation. If tiny asbestos particles float in the air, especially during the manufacturing process, they may be inhaled or swallowed.
Prior to the 1970s, enormous amounts of asbestos were used in commercial construction and shipbuilding. After the health risks of asbestos became known, production of asbestos slowed drastically in the 1970s. Governmental restrictions were placed on its use, and alternative materials became available. Despite these changes, asbestos continues to be used.
Occupations that deal with asbestos and are typically associated with the onset of malignant mesothelioma later in life include asbestos production, insulation work, heating trades, shipyard work, and construction.
The period between asbestos exposure and the development of mesothelioma is generally 35-40 years. Usually, people who develop mesothelioma have been exposed to asbestos for a prolonged period; however, some people with only brief exposures have also developed mesothelioma. On the other hand, not all workers who are heavily exposed develop mesothelioma.
Mesothelioma can also occur in family members and other people living with asbestos workers. It may be a result of exposure to asbestos dust brought home on the clothing and hair of asbestos workers.
In some people with mesothelioma, no specific asbestos exposure can be found. Frequently, such people have worked in a job where the exposure was not recognized or typically associated with asbestos exposure. Mesothelioma without asbestos exposure does occur.
The major known cause of mesothelioma is exposure to asbestos. A known history of asbestos exposure is present in a majority of cases of mesothelioma. Asbestos likely causes cancer by physically irritating the cells. When asbestos fibers are breathed in, they reach the ends of the small airways and penetrate into the pleura (lining of the lung). These fibers may then injure mesothelial cells of the pleura and eventually cause mesothelioma.
The risk of developing mesothelioma rises with the quantity of asbestos exposure. However, genetic factors also play a role in determining who develops the condition. This is probably the reason why all people exposed to high levels of asbestos do not develop mesothelioma.
Although smoking has not been associated with the development of mesothelioma, the combination of smoking and asbestos exposure significantly increases a person's risk of developing lung cancer.
Mesothelioma also has been linked to the following:
Mesothelioma symptoms may not appear until 30 to 50 years after exposure to asbestos fibers. The onset of symptoms is gradual, and a person often experiences symptoms for four to six months before the diagnosis is made.
You should see a healthcare provider if you have any of the following symptoms:
The above-listed symptoms may be caused by mesothelioma or by other, less serious diseases. Only a healthcare provider can make a diagnosis with the help of various exams and tests.
Patients with mesothelioma will usually require treatment by an oncologist (cancer specialist) or pulmonologist (lung specialist).
Chest X-ray: In people with mesothelioma, chest X-ray may show signs of mesothelioma. However, chest X-ray has limited usefulness because the findings of mesothelioma on chest X-ray are nonspecific and observed in other diseases as well.
CT scan: The findings of the CT scan are similar to those of a chest X-ray but are seen better and in more detail. CT is preferred for staging (evaluating the extent of) the tumor.
MRI: In some people, MRI complements the findings of a CT scan. MRI provides a better demonstration of soft tissues (better soft-tissue contrast) and may provide additional information not obtained from other studies.
Positron emission tomography (PET) scan: PET is a procedure in which a radiolabeled substance is used to measure the metabolic activity of the cells. Cancerous cells demonstrate increased metabolic activity. This procedure is being increasingly used to determine the size of the tumor and whether the tumor has spread.
Radiologic findings on X-ray, CT scan, and MRI cannot provide a clear diagnosis of mesothelioma. A history of asbestos exposure and radiologic findings may indicate the presence of mesothelioma, but it is important to stress that a diagnosis of mesothelioma cannot be made exclusively with imaging. Other diseases can look identical to mesothelioma radiographically. A tissue biopsy (a sample of cells is removed for examination under a microscope) is required for a definitive diagnosis.
Thoracoscopy: In this procedure, a small cut is made in the chest wall and a thoracoscope (flexible, lighted tube) is inserted between the two ribs. Thoracoscopy allows the health care professional to look inside the chest and take tissue samples. A pathologist examines these samples for cancer cells. It provides a confirmatory diagnosis in 98% of people with mesothelioma.
When the diagnosis of mesothelioma is confirmed, the tumor stage is determined in order to plan the optimal treatment. Mesothelioma is broadly staged into two categories: localized (the tumor is restricted to the membrane surface where it originated) and advanced (spread to neighboring structures and distant organs and tissues).
Localized mesothelioma is also called stage I mesothelioma.
Advanced mesothelioma can be further classified into the following stages:
Like most cancers, mesothelioma is best treated when it is diagnosed early. Treatment depends on the location of the tumor, how far it has spread, and your age and general health. Stages 1, 2, and some stage-3 mesothelioma may be amenable to potentially curative surgery. Whatever the stage of mesothelioma, there are several types of treatments that can be used.
Traditional treatments for mesothelioma include the following:
Currently, guidelines such as those provided by the National Comprehensive Cancer Network (NCCN) can guide treatment once the disease is diagnosed with certainty. Treatment is best done at centers with experience with this uncommon disease. Often the traditional treatments are used in combination. Aggressive surgery may carry a significant risk of complications and is again best performed by experienced surgeons. A multidisciplinary team is usually convened prior to treatment to plan and coordinate the care of a patient with mesothelioma.
Because mesothelioma is difficult to treat, several new therapies are being evaluated currently. They include the following:
Chemotherapy uses anticancer drugs to attempt to destroy cancer cells. Chemotherapy is a systemic treatment because the drug enters the bloodstream, circulates throughout the body, and kills cancer cells. Because the drugs circulate throughout the body, they can kill normal cells together with cancer cells, leading to side effects. Chemotherapy is often used in combination with other treatment options, especially surgery. Today the combination of two drugs, Pemetrexed and cisplatin has shown the most promise as a mesothelioma treatment.
Radiation therapy is the use of high-energy X-rays or other high-energy rays to destroy cancer cells. Most of the normal cells recover from the injury caused by radiation; however, damage to some of the healthy cells causes the side effects of radiation therapy (nausea, vomiting, fatigue, hair loss, and skin irritation).
Radiation can be given from outside the body using a machine (external radiation therapy), or it can be given with the help of materials producing radiation that are implanted inside the body (internal radiation therapy).
To relieve symptoms and provide pain relief, your fluid from the pleural cavity may be drained by inserting a needle into the chest and applying gentle suction. Drugs may be given through a tube in the chest to prevent more fluid from accumulating.
The objective of surgery is to remove mesothelioma. If the tumor has spread to many organs, it is impossible to remove all the cancer cells from the body. In such cases, surgery may still be done to provide pain relief.
Depending on the stage of the tumor, the surgeon may decide on the type of surgery. Types of surgeries for pleural mesothelioma include pleurectomy and extrapleural pneumonectomy.
Because mesothelioma is difficult to treat, clinical trials are being conducted to find new and better methods of treatment. Research is being conducted at various cancer centers all over the United States. Before any new treatment can be used at large, specialists conduct trials on a limited number of people to ascertain whether the treatment is useful and safe. If you have mesothelioma, you have the option of enrolling in the various clinical trials being conducted.
If you are considering enrolling yourself in a clinical trial, you may find the booklet Taking Part in Clinical Trials: What Cancer Patients Need to Know useful. This booklet published by the National Cancer Institute explains how research studies are done and describe their possible benefits and risks. You can order the booklet by calling Cancer Information Service at 1-800-4-CANCER (1-800-422-6237); TTY at 1-800-332-8615.
Websites giving information about ongoing clinical trials include the following:
In some people, age, other health problems, or advanced disease may make aggressive treatment of mesothelioma difficult. In such people, palliative care (treating the symptoms, but not the disease itself) is an option. Palliative care is a specialized form of care that lessens pain and other symptoms. The goal of palliative care is not to prolong life or hasten death, but rather to enhance the quality of your life while offering support to you and your family. Your doctor should offer you palliative care consultation as part of your mesothelioma treatment planning especially in inoperable mesothelioma or in cases where you are not well enough to undergo such surgery.
If you opt for palliative care, it is very important to communicate openly with your healthcare team. With palliative care, many symptoms of mesothelioma can be substantially reduced. At every visit, you should tell your healthcare provider how you feel, what discomfort you have, and your level of pain.
Palliative care offers you emotional and physical comfort and relief from pain. Other symptoms managed through palliative care include shortness of breath, fatigue, loss of appetite, gastrointestinal problems, skin problems, anxiety, and depression.
Palliative and, eventually, end-of-life care may be given in a hospital, hospice, or nursing home; however, it can also be provided at home. The following organization can help you with palliative and terminal care:
National Hospice and Palliative Care Organization (NHPCO)
http://www.nhpco.org
Hospice Association of America (HAA)
http://www.nahc.org/
Like most cancers, the outlook of mesothelioma depends on how early it is diagnosed and how aggressively it is treated. Without treatment, mesothelioma is fatal within four to eight months.
With trimodal treatment (surgery, chemotherapy, and radiotherapy), survival was noted in some people at 16-19 months. A few people survived for as long as five years.
Because asbestos is the major known cause of mesothelioma, eliminating exposure to asbestos fibers can significantly decrease the risk of mesothelioma.
If you are exposed to asbestos at the workplace, you should wear protective clothing and masks. You should change your clothing before leaving the workplace to avoid carrying any asbestos particles home. Occupational Safety and Health Administration (OSHA) provides useful safety and health information for people exposed to asbestos.
Dealing with a life-threatening disease is difficult. Reading the experiences of other people with mesothelioma helps to cope with the condition. You can access their stories on the following Web pages:
Any environmental substance that irritates the air passages or the lungs is capable of producing a chronic cough with continued exposure. Cigarette smoke is the most common cause of chronic cough. Other cough-producing irritants include dusts, pollens, pet dander, particulate matter, industrial chemicals and pollution, cigar and pipe smoke, and low environmental humidity.
