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).