Mesothelioma

Definition

Mesothelioma is an uncommon disease that causes malignant cancer cells to form within the lining of the chest, abdomen, or around the heart. Its primary cause is believed to be exposure to asbestos.

Description

Malignant mesothelioma is also known as asbestos cancer or simply "meso." Mesothelioma causes cancerous cells to develop in the body's mesothelium, where they can spread to and damage vital organs and tissue. These malignant cells can also metastasize to other regions of the body. Mesothelioma is very difficult to diagnose and responds poorly to most treatment modalities, accounting for a poor prognosis.

The disease derives its name from the mesothelium, a sac-like membrane that protects most of the body's internal organs. It is divided into two distinct protective layers of cells: the visceral (the layer directly surrounding the organ) and the parietal (a sac around the body cavity). By releasing a lubricating fluid, the mesothelium allows the organs to move more freely within the body cavity; for example, the contraction and expansion of the lungs. The mesothelium is also referred to according to where it is located in the body: pleura (chest), peritoneum (abdomen), and pericardium (heart).

Over two-thirds of all mesothelioma cases begin in the pleura region. Pleural mesothelioma spreads through the chest cavity, occasionally developing in the lungs as well. The disease most commonly causes pleural effusion, an excess build-up of fluid inside the chest cavity. This excess fluid increases pressure on the lungs and restricts breathing. In addition, malignant cells can cause the pleural lining to thicken and restrict the breathing space even further.

Peritoneal mesothelioma is the second most common form of the disease, accounting for less than 30% of all cases. Malignant cells form in the peritoneum, affecting the abdomen, bowel, liver, and spleen. Similar to pleural mesothelioma, the disease also causes a build up of excess fluid in the abdominal cavity. Normal bodily functions, such as digestion, can be hindered by the obstruction of organ movement.

Very rare forms of mesothelioma occur in the pericardium, as well as the mesothelium of the male and female reproductive organs. Cystic mesothelioma of the peritoneum, another rare form of the disease, occurs predominantly in women and is more benign in nature.

Malignant mesothelioma takes the form of one of three cell-types: epithelioid (50% to 70% of cases), sarcomatous (7% to 20% of cases), and biphasic/mixed (20% to 35% of cases). Of these cell-types, epithelioid mesothelioma carries the most favorable prognosis, followed by biphasic, and finally sarcomatous (very aggressive).

Mesothelioma remains relatively uncommon in the United States, with approximately 2,500 new cases reported annually. The incidence rates are much higher in Western Europe (over 5,000 cases reported annually). These numbers are expended to climb dramatically over the next 20 years. Older males (median age 60 at diagnosis) are three to five times more likely to develop mesothelioma than women. This is most like do to male predominance in those professions with an increased risk of asbestos exposure.

Causes & symptoms

Approximately 80% of all mesothelioma patients have a history of asbestos exposure. The majority of these patients were employed in an industry that involved the use of asbestos in some fashion. In addition to occupational exposure, household exposure of family members is not uncommon. An exposed individual can carry the asbestos particles on their clothing, skin, and in their hair when they return home, resulting in paraoccupational exposure. Even brief exposure to asbestos, as little as one to two months, can result in long-term consequences. Although the dangers of asbestos have been known for decades, the long latency period of mesothelioma (30 to 40 years) means that majority of patients were already exposed as far back as the 1950s. It is estimated that up to eight million Americans have already been exposed. Several industries, in particular, show a higher incidence of asbestos exposure:

• Insulators (Asbestos workers)
• Boilermakers
• Ship-fitters
• Steel workers
• Maintenance workers
• Plumbers
• Brake mechanics

Symptoms

Mesothelioma is very aggressive once it truly takes hold. However, its initial symptoms are generally non-specific in nature and/or mimic other conditions, such as persistent pneumonia or gastronomical disorders. Some patients will exhibit no symptoms at all. As such, proper evaluation and diagnosis are commonly delayed and must be confirmed by a doctor.

Patients suffering from pleural mesothelioma most commonly exhibit signs of dyspnea, pleural effusions, and/or chest pain. The majority of pleural effusion symptoms will exhibit in the right lung (60% of the time). Patients may also exhibit persistent cough, weight loss, weakness, fever, and difficulty swallowing.

Patients suffering from peritoneal mesothelioma most commonly exhibit signs of pain and/or swelling in the abdomen from fluid retention or tumor growth. Weight loss, nausea, bowel obstruction, anemia, fever, and swelling in the legs and/or feet are also known symptoms.

Diagnosis

Only a physician can properly diagnose mesothelioma. A review of the patient's medical history, including any past exposure to asbestos, should be conducted for any patient displaying dyspnea, chest pain, fluid build-up, or pain and/or swelling in the abdomen. This review is followed up with a complete physical examination, which should involve the use of imaging techniques. X rays, computed tomography (CT) scans, and magnetic resonance (MRI) scans of the chest and/or abdomen, as well as lung function, can provide the doctor with critical diagnostic information. Although positron emission tomography scans are expensive and not covered under most insurance, this diagnostic tool has proven very useful in determining tumor sites and staging of the disease.

If indicated, the doctor may wish to internally examine the patient's chest and/or abdominal cavity. These diagnostic procedures, known as thoracoscopy (chest) and peritoneoscopy (abdomen), are usually conducted in a hospital setting. Both procedures involve a fiber-optic imaging tool being inserted into the patient through an incision. These endoscopic tools will provide the doctor with a closer look at the body cavity, and any abnormal tissue or fluid build-up found therein. Excess fluid can be suctioned out through a needle or tube, in a process known as thoracentesis (for the chest) or paracentesis (for the abdomen). Additionally, the doctor may perform a biopsy of any abnormal tissue they discover during this time. Pathological examination of abnormal tissue, as well as fluid, remains the only effective method of confirming the diagnosis of mesothelioma. Biopsy will also assist the doctor in properly staging the disease's progression.

Once a confirmation of malignant mesothelioma has been established, the doctor will conduct further tests to determine the extent to which the primary disease has spread. This diagnostic process is known as "staging." Malignant pleural mesothelioma of can be broken into four stages:

• Localized Malignant Mesothelioma (Stage 1)—Cancer is present in the right or left pleura. May involve the lung, the pericardium, or diaphragm on that side.
• Advanced Malignant Mesothelioma (Stage 2)—Cancer has spread beyond the right or left pleura to lymph nodes on that side. May involve the lung, the pericardium, or diaphragm on that side.
• Advanced Malignant Mesothelioma (Stage 3)—Cancer has spread into the chest wall, diaphragm, ribs, heart, esophagus, or through the abdominal lining. Nearby lymph nodes may or may not be involved.
• Advanced Malignant Mesothelioma (Stage 4)—Cancer shows evidence of metastasis or spread through the bloodstream to distant organs and/or tissues.

Recurrent malignant mesothelioma may also occur, where the cancer returns in its original location or elsewhere in the body even after treatment.

Treatment

There are three traditional treatment modalities for mesothelioma: surgery, radiation therapy, and chemotherapy. The location and the stage of the disease, as well as the patient's age and general health, will determine which treatment should be utilized. Additionally, these modalities can be combined if indicated. Indeed, the multimodality approach appears to provide the most positive results for treating mesothelioma.

Surgery, the most common treatment, involves the removal of the tumor. In the early stages of mesothelioma, this only involves removal of a section of the mesothelium and surrounding tissue, but may require removing part of the diaphragm as well. For more advanced stages of the disease, removing the entire lung may be the only option, which is known as pneumonectomy.

Radiation therapy, also known as radiotherapy, destroys and shrinks the cancer cells through various types of radiation. Both external (such as a machine) and internal (such as radioisotopes) radiation therapies can be utilized effectively to treat malignant mesothelioma.

Finally, chemotherapy, a systemic treatment modality, uses anticancer drugs to destroy the cancerous cells throughout the body. The majority of drugs used to treat mesothelioma are delivered intravenously. The effectiveness of intracavitary chemotherapy, the process of directly injecting the drugs into the chest or abdominal cavity, is being studied.

Pain and other symptoms caused by fluid build-up around the chest and/or abdomen can be treated by drain excess fluid through a needle or tube. These procedures are known as thoracentesis (chest) and paracentesis (abdomen). Drugs, radiotherapy, and surgery can also relieve or prevent further fluid accumulation.

Physicians are currently studying other treatment modalities, such as immunotherapy, gene therapy, and intraoperative photodynamic therapy.

Alternative treatment

Due to the poor prognosis associated with mesothelioma, regardless of proper treatment, in many cases palliative care is the preferred, and only, option available to patients. This is particularly true for the advanced stages of the disease. By treating the symptoms rather than the disease itself, the goal of this approach is to obtain "quality" of life instead of "quantity" of life. Palliative care aims to relieve the patient s discomfort caused by dyspnea and pain. Chemotherapy, radiation, and/or surgical pleurodeis, in combination with effective management of pain and respiratory function should form the basis of proper palliative care of mesothelioma. Techniques to reduce stress, such as acupuncture, aromatherapy, massage, and reflexology, can provide addition benefit to the patient's sense of well-being.

Prognosis

The stage and location, what cell-type is involved, as well as the patient's age and histology factor greatly on life expectancy. Unfortunately, even with aggressive treatment, the prognosis for mesothelioma patients is poor. Pleural mesothelioma offers a median survival time of approximately 16 to 17 months after initial symptoms. Prognosis for peritoneal mesothelioma is poorer and has a median survival time of only ten months after initial symptoms. Unfortunately, the more advanced stages of mesothelioma may offer as little as four or five month's survival time.

The survival time for patients with localized mesothelioma can be extended several months with aggressive therapy, with roughly 20% of patients surviving past the five-year mark. Therapy programs recently developed at leading cancer centers have extended this survival time even further. Dr. Sugarbaker, of the Brigham and Women's Center in Boston, has achieved a median of 40% survival rate at five years with his treatment regimen for pleural mesothelioma, as reported in the Journal of Thoracic and Cardiovascular Surgery. Other programs are also exhibiting favorable results. However, despite such successes, no cure for mesothelioma currently exists.

KEY TERMS

Asbestos— A naturally occurring mineral, utilized worldwide for its durability and heat resistant qualities. Extremely fibrous in nature, asbestos particles can easily enter the respiratory system and damage sensitive tissue. This damage can result in asbestosis, mesothelioma, and lung cancer.

Dyspnea— A difficulty in breathing or shortness of breath, typically associated with some form of heart or lung disease. Also known as air hunger.

Mesothelium— A membrane/sac that that protects the body's major internal organs and allows them freedom of movement (for example, lung contractions). The mesothelium is comprised of several regions, including the abdominal cavity (peritoneum), the chest cavity (pleura), and pericardium (heart).

Pleural effusion— An abnormal accumulation of fluid in the pleura, a fibrous membrane that lines the inside of the chest cavity and protects the lungs. This accumulation can cause shortness of breath, cough, and chest pain.

Prevention

Avoiding or limiting exposure to asbestos is the best way to prevent mesothelioma. Unfortunately, because of the significant delay between exposure and onset (30 to 40 years), it is probably too late to prevent the development of mesothelioma for most patients. Not smoking may slow the disease's progression and/ or prevent other further complications associated with asbestos exposure.

Resources

BOOKS

Jaurand, Marie-Claude, and Jean Bignon (eds). The Mesothelial Cell and Mesothelioma. New York: Marcel Dekker, 1994.

Robinson, Bruce, and A. Philippe Chahinian (eds). Mesothelioma. London: Martin Dunitz, 2002.

PERIODICALS

Pistolesi, Massimo, and James Rusthoven. "Malignant Pleural Mesothelioma." Chest 126 (October, 2004): 1318-1329

Sugarbaker, David, et al. "Resection Margins, Extrapleural Nodal Status, and Cell Type Determine Postoperative Long-Term Survival in Trimodality Therapy of Malignant Pleural Mesothelioma." Journal of Thoracic and Cardiovascular Surgery 117 (January, 1999): 54-65

van Ruth, Serge, Paul Baas, and Frans Zoetmulder. "Surgical Treatment of Malignant Pleural Mesothelioma." Chest 123 (February, 2003): 551-561

ORGANIZATIONS

Mesothelioma Research Foundation of America. 5716 Corsa Ave., Suite 203, Westlake Village, CA 91362. (800) 281-9804. 〈http://www.mesothelioma-rfa.org〉.

The Mesothelioma Center. 1030 Fifth Ave., Pittsburgh, PA 15219. (412) 471-3980. 〈http://mesotheliomacenter.org〉.

OTHER

"Malignant Mesothelioma." National Cancer Institute 〈http://www.nci.nih.gov/cancertopics/types/malignantmesothelioma/〉.

"Mesothelioma." Mesothelioma Information 〈http://www.mesoinfo.com〉.

"Mesothelioma." Mesothelioma Web 〈http://www.mesotheliomaweb.org〉.

Mesothelioma

Definition

Mesothelioma is a rare form of cancer. In mesothelioma, malignant cells are found in the sac lining of the chest (the pleura) or the abdomen (the peritoneum). The majority of people with mesothelioma have a history of jobs that exposed them to asbestos, an insulation material.

Description

In the chest and abdominal cavities, as well as in the cavity around the heart (pericardial sac), there is a layer of specialized cells called mesothelial cells. These cells also surround the outer surface of most internal organs. These cells form tissue called mesothelium.

The mesothelium performs a protective function for the internal organs by producing a lubricating fluid that permits the organs to move around. For example, this fluid makes it easier for the lungs to move inside the chest while a person breathes. The mesothelium of the abdomen is known as the peritoneum, and the mesothelium of the chest is called the pleura. The pericardium refers to the mesothelium of the pericardial cavity.

There are three primary types of malignant mesotheliomas:

• Epithelioid. About 50% to 70% of mesotheliomas are of this type and have the best outlook for survival.
• Sarcomatoid. Approximately 7% to 20% of cases are of this type.
• Mixed/biphasic. From 20% to 35% of mesothelioma cases fall into this category.

Approximately three fourths of all mesotheliomas begin in the chest cavity and are known as pleural mesotheliomas. Peritoneal mesotheliomas begin in the abdomen, and make up around 10% to 20% of all cases. Mesotheliomas arising in the cavity around the heart are quite rare.

Demographics

Mesothelioma is a fairly rare form of cancer. According to the American Cancer Society, there are an estimated 2, 000 to 3, 000 new cases per year of the disease in the United States, but this figure seems to be rising. This rising figure is related to the widespread use of asbestos from the 1940s to the end of the 1970s. European researchers studying the disease expect deaths from mesothelioma to peak around the year 2020 and then drop off, because asbestos use has been cut back greatly since the early 1980s.

The average age of a person with mesothelioma is 50 to 70 years old. It affects men three to five times more often than women and is less common in African-Americans than in Caucasian Americans.

Causes and symptoms

The primary risk factor for developing mesothelioma is asbestos exposure. In the past, asbestos was used as a very effective type of insulation. The use of this material, however, has been declining since the link between asbestos and mesothelioma has become known. It is thought that when the fibers of asbestos are inhaled, some of them reach the ends of the small airways and penetrate into the pleural lining. There the fibers may directly harm mesothelial cells and eventually cause mesothelioma. If the fibers are swallowed, they can reach the abdominal cavity, where they can contribute to the formation of peritoneal mesothelioma.

Exposure to certain types of radiation as well as to a chemical related to asbestos known as zeolite has also been related to incidences of mesothelioma.

The early symptoms of mesothelioma are often ignored, because they may be caused by a variety of ailments. These symptoms include:

• pain in the lower back or at the side of the chest
• shortness of breath
• difficulty swallowing
• cough
• fever
• fatigue
• abdominal pain, weight loss , and nausea and vomiting (symptoms of peritoneal mesothelioma)

Diagnosis

A doctor should be seen if a person experiences shortness of breath, chest pain, or pain or swelling in the abdomen. If these symptoms are present, the doctor may order an x ray of the abdomen or chest. The doctor will do a complete physical examination and take a thorough medical history. Then, one or more of the following methods may be used to ascertain whether mesothelioma is present.

• Imaging tests. These tests may include x rays, computed tomography (CT scans), or magnetic resonance imaging (MRI) to allow the doctor to visualize the area in question. These studies will help determine the location, size, and extent of the cancer.
• Pleural biopsy . Diagnosing mesothelioma requires an adequate biopsy specimen. However, because mesothelioma usually arises from the lower part of the diaphragmatic and/or parietal pleura, obtaining enough tissue may be difficult. A simple, or closed, pleural biopsy involves the insertion of a needle into the chest cavity to obtain tissue from the pleural membrane for analysis. This technique is minimally invasive and normally requires only local anesthesia. This technique, however, may not provide adequate material for the necessary stains of the tissue to make a diagnosis of mesothelioma. Moreover, since the biopsy is not done under direct vision, the sample may not be exactly in the area of the tumor. If the diagnosis cannot be made with this relatively noninvasive technique, an adequate tissue sample usually can be obtained via an open pleural biopsy. In this approach, a surgeon makes an incision on the patient's side and goes into the pleural space. This method allows maximum exploration of the pleural membranes as well. However, the technique requires general anesthesia.
• Thoracoscopy . A thoracoscopy, which is a relatively new technique, allows the doctor to look directly into the chest (pleural) cavity at the tumor and during the same operation to also take a tissue sample for laboratory analysis. The thoracoscopy is performed by making a small incision into the chest and using a tiny video camera to inspect the region. The doctor can then use forceps to obtain a tissue biopsy. A laparoscopy , a similar operation, is used to obtain a biopsy of a peritoneal tumor.
• Bronchoscopy . A bronchoscopy, which examines the airways, or a mediastinoscopy , which looks at the lymph nodes in the chest, allows the doctor to look at the area using a lighted tube. Samples may be taken with a needle and sent to the lab to find out if cancer cells are present. However, bronchoscopy and mediastinoscopy are not that effective for diagnosing mesothelioma, as the disease is seldom found within the airways or the lymph nodes.
• Surgery. This lets the doctor obtain a larger tumor sample or, on occasion, the entire tumor.

Diagnosing mesothelioma is often difficult, even with tissue biopsies. Microscopically, mesothelioma is often difficult to distinguish from several other forms of cancer. For this reason, certain laboratory tests are performed to help correctly diagnose mesothelioma. Some of these tests involve using antibodies to distinguish lung cancer from mesothelioma. Sometimes the tissue samples must be viewed under an electron microscope in order to get the correct diagnosis.

Treatment team

A person with symptoms of mesothelioma will most likely seek help from a primary physician initially. During the diagnostic phase, various technicians will perform the imaging studies . A specially trained physician—a thoracic surgeon or, rarely, a pulmonologist— performs other diagnostic tests like pleural biopsy and thoracoscopy. A pathologist will view the tissue samples and make the tissue diagnosis. Following diagnosis, the patient will be offered some form of treatment, which may entail surgery, radiation therapy , chemotherapy , or a combination of these. The patient may receive care from a thoracic surgeon, an anesthesiologist, medical and radiation oncologists, and specially trained nurses who administer chemotherapy.

Clinical staging, treatments, and prognosis

The treatment and outlook for those with mesothelioma depends a great deal on the stage of their cancer. Because the most frequently occurring type of mesothelioma is pleural, and it is also the one most studied, it is the only type for which a staging system exists. The following stages are based on a system known as the Butchart system, which divides mesothelioma into four stages:

• Stage I: Mesothelioma is found within the right or the left pleura and may also involve the lung, the pericardium, or the diaphragm on the same side.
• Stage II: In this stage, mesothelioma has spread to the chest wall or involves the esophagus, the heart, or the pleura on both sides. The lymph nodes in the chest may be involved as well.
• Stage III: Mesothelioma has gone through the diaphragm and into the lining of the abdominal cavity. Additional lymph nodes besides those in the chest may be involved.
• Stage IV: There is evidence that mesothelioma has spread through the bloodstream to distant organs or tissues.

Another system of staging mesothelioma is based on a TNM system (T=tumor, N=spread to lymph nodes, and M=metastasis). There are minor differences between this and the Butchart system. It is more detailed and precise, but the original Butchart system is still the one most often used to describe pleural mesotheliomas.

There are treatments available for all patients with malignant mesothelioma. The three kinds of treatment used are surgery, radiation therapy, and chemotherapy.

Surgery is a common treatment for mesothelioma. It is not an option unless the cancer is limited to one place and unless the person can withstand the surgery. During surgery, the physician may remove a portion of the lining of the chest (pleurectomy) or abdomen (peritonectomy) and some of the tissue surrounding it. Depending on the extent the disease has spread, a lung may also require removal (extrapleural pneumonectomy ). Occasionally, a portion of the diaphragm is taken out as well. If treatment is not possible, other less invasive measures can be used to relieve the patient's symptoms. For example, a needle placed into the chest cavity (thoracentesis ) can remove excess fluid in the chest. If recurrence of fluid causes symptoms, a nonsurgical or surgical method can be used to scar the lining of lung cavity and cause it to adhere to the lung. The procedure obliterates the pleural space and thus prevents the fluid from reaccumulating. (This procedure is called sclerosis or sclerotherapy.) These methods are called palliative, for they are not meant to cure the cancer but to improve symptoms.

Radiation therapy uses high-energy x rays to kill cancer cells and cause tumor shrinkage. It is rarely used as the primary treatment for pleural mesothelioma in those patients for whom surgery is not an option. It may also be used as an adjunct to surgery or as a method of alleviating various symptoms like trouble with swallowing, pain, and shortness of breath.

Chemotherapy involves the use of drugs to kill cancer cells. The most commonly used drugs are doxorubicin , cisplatin , and methotrexate . The medicines are delivered into a vein or taken by mouth. In the treatment of mesothelioma, they may also be injected directly into the chest or abdominal cavity. Chemotherapy may be given as the main treatment or may be an addition to surgery, depending on the type and stage of the cancer.

A new treatment being studied for early stages of mesothelioma confined to the chest is called intraoperative photodynamic therapy. This treatment uses special drugs that make cancer cells more sensitive to killing by a laser light. The drugs are given several days before surgery. During surgery, the special light is used to shine on the pleura.

By the time symptoms show up and mesothelioma is diagnosed, the disease is often advanced. The average survival period after diagnosis is about one year. If the cancer is found before it has spread and it is treated aggressively, about half of the patients will live two years, and approximately 20% will survive five years.

Alternative and complementary therapies

There are no proven effective alternative therapies for mesothelioma. Because the prognosis is often poor, many patients may be interested in trying other avenues of treatment. Patients should first consult with their physicians prior to trying any of these methods. There are many well-studied complementary treatments that may increase a patient's comfort and sense of well-being. These may include meditation to aid in relaxation, massage to decrease pain, and guided imagery to help prevent nausea.

Coping with cancer treatment

Coping with cancer treatment can be difficult and exhausting. It can be very helpful for the patient receiving therapy for mesothelioma to find a group of family and friends who can aid with household responsibilities, provide transportation, and give psychological support. The patient should not feel a need to rush back to normal activities after treatment is completed.

Clinical trials

A great deal of research is being performed in the area of mesothelioma. Much of the research is focused on finding out how asbestos changes the mesothelial cells to cause these cancers. In addition, new combinations of treatments are being tested, along with gene therapy. A variety of clinical trials are testing new chemotherapy drugs and immunotherapy. Some of these treatments use hormonelike substances called inter-leukins and interferons that activate the immune system.

Prevention

The best method of preventing mesothelioma is to avoid or limit exposure to asbestos. People who might experience asbestos exposure at work include miners, insulation manufacturers, construction workers, ship builders, and factory workers.

Special concerns

Mesothelioma is a serious disease with a poor long-term prognosis. Patients with this cancer should communicate their wishes regarding treatment to their family and physicians.

Resources

BOOKS

Buckman, Dr. Robert. What You Really Need to Know About Cancer: A Comprehensive Guide for Patients and Their Families. Baltimore: Johns Hopkins University Press, 1997.

PERIODICALS

Apgar, Barbara. "Diagnosis of Malignant Pleural Mesothelioma." American Family Physician (15 January 2000): 536.

Savastano, Dina. "Prolonging Life for Mesothelioma Patients." Radiologic Technology (March-April 1998): 365.

ORGANIZATIONS

American Cancer Society. (800) ACS-2345. <http://www.cancer.org>.

National Cancer Institute. Building 31, Room 10A31, 31 Cen ter Drive, MSC 2580, Bethesda, MD 20892-2580. (800) 4-CANCER. <http://www.nci.nih.gov>.

Deanna Swartout-Corbeil, R.N.

QUESTIONS TO ASK THE DOCTOR

• What type of mesothelioma do I have?
• Has my cancer spread beyond the primary site?
• What stage is my cancer in? What treatment options are there?
• What is my prognosis?
• Are there experimental therapies I may benefit from? Where are they being performed?

KEY TERMS

Asbestos

—A group of naturally occurring fibrous minerals, found in soil and rocks around the world. These minerals are composed of magnesium, silicon, and other elements. Asbestos has been used as an insulating material since ancient times. Exposure to asbestos dust is the primary risk factor for developing mesothelioma.

MESOTHELIOMA

Mesothelioma is a rare cancer of the lining of the chest, the abdomen, or other tissues. It has become increasingly more frequent since 1900, however, paralleling the use of asbestos. Exposure to asbestos is the most common cause of this disease, with the vast majority of cases occurring following exposures that may have taken place decades earlier. Mesotheliomas can be seen ten years after first exposure, but they peak at three to four decades after exposure. The risk is lifelong, and the prognosis is extremely poor, with death often occurring within twelve months of diagnosis, no matter what the treatment. Newer, extensive surgical techniques may alter this historical experience.

All fiber types of asbestos cause this disease, although there is continuing controversy over the differential ability of the different fiber types to do so. The one other recognized cause of this disease in humans is another group of fibrous materials called zeolites. In animal studies, however, a wide variety of other fibers have been known to cause mesotheliomas.

Mesotheliomas appear as several cellular patterns and may be difficult to diagnose. Special panels of experts are available to assist with making these evaluations. The most common lesions with which these may be confused are lung cancers.

Arthur L. Frank

(see also: Asbestos; Occupational Safety and Health )

Bibliography

Osinubi, O. Y.; Gochfeld, M.; and Kipen, H. M. (2000). "Health Effects of Asbestos and Nonasbestos Fibers." Environmental Health Perspectives 108(54):665–674.

Selikoff, I. J., and Lee, D. H. K. (1978). Asbestos and Disease. New York: Academic Press.

mesothelioma (mes-oh-th'ee-li-oh-mă) n. a tumour of the pleura, peritoneum, or pericardium. The occurrence of pleural mesothelioma is often due to exposure to asbestos dust (see asbestosis).