Mesothelioma is a rare form of cancer that attacks the mesothelium, a membrane that surrounds and protects many of the body’s internal organs as well as the walls of the chest and abdominal cavities. The term almost always refers to malignant mesothelioma, as benign cases of the disease are a small fraction of the overall occurrences.
Mesothelioma has become a widely known and publicized disease despite its relative infrequency because of the fact that the only proven cause for its development is asbestos exposure – specifically, inhalation or ingestion of tiny, microscopic asbestos fibers that eventually cause the development of mesothelioma. Asbestos related diseases are among the primary industrial medical afflictions of the nineteenth and twentieth centuries.
The disease has an unusually long period of latency. Persons exposed to asbestos may not develop symptoms of asbestos related disease for twenty to fifty years after the asbestos exposure has taken place. For that reason, the widespread use of asbestos through the 1970s is still causing new diagnoses of mesothelioma today among workers who have long been retired. Although today there are only about 3,000 new cases of the disease diagnosed in the U.S. annually, mesothelioma has taken tens of thousands of lives in this country since asbestos was introduced as an industrial material in the late 19th century.
Causes of Mesothelioma
Asbestos fibers are the primary cause of mesothelioma. They are microscopic, cannot be seen with the human eye and when they are ingested or inhaled go unnoticed. Asbestos fibers are given off by asbestos products that have deteriorated and become “friable,” which means that they easily crumble – at which point the fibers can become airborne in dust clouds. In thousands of industrial sites and repair shops where asbestos insulation or other products were used, workers inhaled asbestos fibers on the job – sometimes on a daily basis.
When asbestos fibers are inhaled or ingested, the human body cannot excrete them through any natural means such as coughing, sneezing or any other physiological function. The fibers remain within the body, eventually embedding themselves in tissue; in most cases that tissue is the mesothelium. Asbestos fibers remain in the body forever; eventually they begin to cause problems with the mesothelium tissue. They can cause abnormal cells to develop and those cells begin to reproduce uncontrollably. Often they are cancerous cells, which begin to form the diffuse tumors that characterize most cases of mesothelioma.
The primary cause of asbestos exposure has always been job related. Through World War II exposure occurred in asbestos mines and mills, in textile and pulp & paper mills, in auto assembly plants, steel mills, auto brake shops, in the shipbuilding industry, as well as a large percentage of veterans. Workers in refineries, power plants and petrochemical plants have historically been at risk because of the use of asbestos products for insulation. Construction workers using asbestos laced cement, and asbestos insulation in buildings and the installation of heating systems have historically been at high risk for asbestos exposure.
During the first three quarters of the twentieth century, family members of workers who were subject to on the job exposure were at risk of inhaling asbestos fibers from clothing worn on the job and brought home by the workers. People who lived near asbestos mills were also exposed to asbestos laden clouds of dust. People living in households with asbestos workers were found to have significantly elevated lung burdens of asbestos, often in the same range as found in individuals occupationally exposed to asbestos, such as shipyard workers.
In 1990, the U.S. Occupational Safety and Health Administration “estimated that approximately 568,000 workers in production and services industries and 114,000 workers in construction industries potentially were exposed to asbestos”.
Types of Mesothelioma
The key to understanding mesothelioma is understanding the various locations that the mesothelium is found and the role that it plays. The lungs are surrounded by a portion of the mesothelium, and the chest cavity wall opposite the lungs is also covered by the mesothelium. These two layers of tissue comprise the pleura, or pleural mesothelium. Another portion of the mesothelium wraps around the heart; this tissue is known as the pericardium. The third important portion of the mesothelium covers the abdominal cavity wall; this portion of the protective tissue is called the peritoneum, or peritoneal mesothelium. The three main malignant types of mesothelioma are:
Pleural Mesothelioma develops in the lining of the lungs. It accounts for about seventy percent of all malignant mesothelioma cases. Because asbestos fibers that affect humans are most commonly inhaled the diseases they cause are most often in or around the lungs.
Peritoneal Mesothelioma develops in the abdominal cavity and often attacks the liver, kidneys and other organs. About fifteen to twenty percent of all mesothelioma cases develop in the peritoneum.
Pericardial Mesothelioma impacts the sac around the heart, is exceedingly rare – occurring in about five percent of all cases. Pericardial mesothelioma can have a fatal impact on cardiovascular function because of the pressure the swollen pericardium applies on the heart.
Signs and Symptoms of Mesothelioma
Three medical characteristics of this disease make it particularly insidious. One is the fact that mesothelioma has a latency period that makes the disease far removed from its cause and that much more difficult to diagnose. The second problem with mesothelioma symptoms is the fact that so many of them are similar to symptoms found in far more common afflictions. Finally, because of the latency involved with the onset of mesothelioma and often with asbestosis, the disease usually impacts people entering into their senior years, when medical problems become more common. Diagnosing a rare disease such as mesothelioma under these circumstances often takes an extended period of time.
The most common symptoms for pleural mesothelioma are:
- A dry, persistent cough
- Chronic chest pain
- Shortness of breath
- Weight loss
- Fever, night sweats, sleeplessness
All of these symptoms can be easily associated with far more common physical problems such as pneumonia, chronic obstructive pulmonary disease (COPD), bronchitis, or the onset of lung cancer. If the patient has been a smoker, the diagnosing physician is going to be looking for these diseases first.
The symptoms for peritoneal mesothelioma include:
- A swollen abdomen
- Abdominal Pain
- Bowel Obstruction
- Fluid accumulation in the abdomen
Many of these symptoms are consistent with liver disease, intestinal disorders or kidney malfunctions. The fact that mesothelioma tumors are difficult to see with medical imaging systems make early diagnosis of this disease a rarity.
The symptoms for pericardial mesothelioma include:
- Heart palpitations and irregular heartbeat
- Chest pain
- Shortness of breath
- Fatigue after brief activity
- Persistent coughing
Heart disease is perhaps the most common serious illness among people over fifty years of disease, and several forms of cardiovascular problems result in similar symptoms. A pulmonary embolism, cardiovascular thrombosis (blocked artery) and congestive heart disease all show these characteristics and they are usually the diseases attending physicians look for first.
Diagnosis of Mesothelioma
Because mesothelioma is cancer that develops upon a membrane, more often than not it develops as a diffuse form of cancer rather than as a singular mass, or tumor. A series of small tumors spread across the mesothelium membrane are much more difficult to identify with medical imaging equipment than a single tumor is. For that reason X-rays, CT scans and MRI exams usually aren’t enough for a mesothelioma diagnosis.
The most common form of the disease, pleural mesothelioma almost always causes pleural effusion, or excessive fluid accumulation, to develop as a primary symptom once the disease begins to advance. Once this condition is established the physician can draw out some of that fluid with a surgical needle to analyze the cell content in the lab. Usually a biopsy extracting a small piece of mesothelial tissue is also conducted. Analyses of these samples will generally expose the existence of malignant cells.
A similar approach is often taken with peritoneal mesothelioma, which commonly causes fluid accumulation in the abdomen. A tissue sample from the abdominal wall extracted with a laparoscope along with a fluid sample help to determine the presence of malignant cells. Analysis of kidney and liver functions and protein levels can help to eliminate other potential causes of the symptoms.
Mesothelioma Treatment Options
Surgery is often the choice when mesothelioma is diagnosed early enough, such as a stage I and stage II mesothelioma. In many cases with pleural mesothelioma this means a pleurectomy, a procedure where the entire pleura is removed. In cases where pleural effusion has been severe, the two surfaces of the pleura might be fused in a process called pleurodesis; generally this is a palliative treatment. Many procedures also take a piece of the lung. An extrapleural pneumonectomy removes part of the lung, part of the diaphragm, part of the pericardium and part of the parietal pleura, which is the tissue covering the chest wall.
Surgery with peritoneal mesothelioma follows a similar model, except that removing nearby organs is not always a viable option as it is with a pneumonectomy. Surgery on the pericardium often occurs on an emergency basis as mesothelioma causes the membrane to swell and put dangerous pressure on the four chambers of the heart.
The use of chemotherapy is widespread in mesothelioma treatment; in recent years it is almost always conducted in conjunction with a radiotherapy program. Most chemotherapy drugs have not proven to be terribly effective against mesothelioma; there are two that have been approved by the FDA thus far for mesothelioma treatment. Researchers are constantly searching for innovative methods to attack malignant mesothelioma cells and avoid damaging healthy cells in the mesothelium membrane. Often chemotherapy is used in tandem, especially when treating biphasic mesothelioma – a form of the disease that features two types of malignant cells. Surgery, chemotherapy and radiotherapy together are referred to as multimodality therapy.
Recently there has been some use of radiotherapy during the surgical process itself. Rather than target cancerous cells with radioactive ions the tissue is targeted directly while the patient is on the operating table. Chemotherapy drugs have been applied in a similar fashion, to give a more powerful application of the treatment than can be provided by intravenous delivery; one such procedure called Heated Intraoperative Intraperitoneal Chemotherapy used heated medication in a peritoneal mesothelioma surgery.
Other options include immunotherapy and other experimental concepts such as gene therapy. These concepts are creative efforts at attacking cancer cells in new and innovative ways. While they remain in the seminal state, hopefully continued research and trial activity will yield results.
Clinical Trials for Mesothelioma
Clinical trials are staged for the benefit of medical research, but they are also a prerequisite for the approval of a new medication or new treatment use of an existing medication by the FDA. That process is divided into stage I, stage II and stage III procedures. It is the stage III studies that are conducted on groups of humans in order to determine the efficacy of a treatment.
There are usually several mesothelioma clinical trials are occurring at any given time, being conducted at one or several locations. It is not easy to find mesothelioma patients who are in condition to participate in a lengthy research project, so recruiting is generally conducted at several locations. Many of these trials involve the use of pemetrexed, marketed under the name Alimta. This is the only drug that has been approved by the FDA for mesothelioma treatment and it is generally used with patients who are not candidates for surgical treatment. Many clinical trials have been conducted using pemetrexed and other effective cancer chemotherapy drugs, cisplatin in particular.
But clinical trials continue not only for chemotherapy options but for new treatment concepts such as immunotherapy.
Prognosis and Life Expectancy for Mesothelioma Patients
Prognosis for mesothelioma patients is usually a question of life expectancy rather than recovery. The figures vary for types of mesothelioma, for treatment modalities and, to an extent, on who you ask. Often diagnosis of this disease is a lengthy process, which means that it has advanced significantly since the symptoms first manifested. One of the issues is the nature of the cells being attacked; epithelial mesothelioma patients have an average survival rate of about one year, while those diagnosed with the more unusual sarcomatoid mesothelioma, or biphasic mesothelioma (a combination of the two cell types) is closer to six months. These are average figures; the percentage of people who live beyond one year is significant but most figures for mesothelioma and morbidity are based on limited case studies.
These figures are changing slowly as diagnoses occur more readily, as some forms of chemotherapy prove to be effective against some forms of mesothelioma, and as new treatment modalities are tried and found to help. The overall gain in average survival time is a matter of weeks or months with these clinical tests, but slow progress is being made.
There are also always exceptions to these rules. Many patients who respond well to surgery and chemotherapy live on for two years or more. One of the issues that comes into play with these poor prognosis figures is the fact that so many mesothelioma patients are elderly and have other health problems as well. Often a patient does not have the constitution to withstand major surgery, so resection is not an option.
Legal Options for Mesothelioma Victims
Asbestos lawsuits comprise the largest single civil tort in the history of the nation. More suits have been filed seeking damages for health problems caused by asbestos than for any other civil legal complaint. Hundreds of thousands of American workers have been impacted by mesothelioma and asbestosis over the last half century and many more are getting sick today. The continued diagnosis of mesothelioma is expected to continue at the current rate for another five to ten years.
If you or a family member has a medical problem that you believe is related to asbestos exposure, you should be in touch with an experienced asbestos lawyers who can assist you by providing the specialized legal help that is required in asbestos and mesothelioma liability cases.
- Brigham and Womens Hospital, International Mesothelioma Program, Mesothelioma Facts, 2010
- NIH National Toxicology Program, Report on Carcinogens, 11th Edition
- http://www.cancer.gov/cancertopics/factsheet/sites-types/mesothelioma, Mesothelioma Questions and Answers
- PubMed, Analysis of Latency Time…in Asbestos Related Malignant Mesothelioma, National Institute for Occupational Safety and Prevention, Rome, Italy, 2007
- Mesothelioma Applied Research Foundation Clinical Presentation, Diagnosis, and Staging of Malignant Pleural Mesothelioma January 2009
- American Cancer Society, Treatment of Mesothelioma based on Extent of the Cancer
- Journal of Clinical Oncology, Phase III Study of Pemetrexed in Combination With Cisplatin Versus Cisplatin Alone in Patients With Malignant Pleural Mesothelioma, Vogelzang, Rusthoven et al, 2003
- Winston Tan, M.D. Mayo Medical School, Mesothelioma, Medscape March 2009