Mesothelioma
Definition
Mesothelioma is a rare type of cancer that develops in the mesothelial cells that lines many organs and body cavities. The mesothelium (composed of mesothelial cells) is the membrane that lines three of the body's cavities, and depending on what cavity it lines it is given a specific name: the thoracic cavity (pleura), abdominal cavity (peritoneum), and the heart sac (pericardium).
Epidemiology
Approximately 2,000 to 3,000 cases of mesothelioma are diagnosed each year in the United States, comprising around 3 percent of all cancer diagnoses. This cancer occurs about four times more frequently in men than in women. All forms of mesothelioma, except for benign mesothelioma, are invariably fatal. A mesothelioma prognosis is almost always poor and most studies report a median survival of less than one year, but the prognosis really depends on how early the cancer is diagnosed and how aggressively it is treated.
Mesothelioma is caused by asbestos exposure. Asbestos is a naturally-occurring fibrous substance that was widely used in the twentieth century in a number of different industries. Popular because of its durability, fire resistance, and insulating properties, it was regularly used in the manufacture of several thousand different products, up until the time that asbestos warnings were issued in the mid-1970s. It is estimated that approximately 80 to 90 percent of mesothelioma cases are caused by asbestos exposure.
Although statistics have shown a growing number of individuals who have never worked with asbestos are suffering with asbestos-related illness, most documented cases of such diseases are caused by occupational exposure. This is due to the likeliness of repeated exposure, which occurs through standard operations in a variety of industries and jobsites.
Naturally, jobsites such as asbestos mines, processing plants, and manufacturing plants where asbestos products were made, have a legacy of high occupational exposure. However, there are many other jobsites such as shipyards, auto-manufacturing plants, metalworks, oil refineries, power plants, and chemical plants that also share a long history of asbestos exposure as well. Those who worked at these jobsites during the 1900's were probably exposed to a number of asbestos-containing products and materials and are now at risk of developing mesothelioma and other asbestos-related illnesses.
Certain occupations also carry an elevated risk of asbestos exposure. Because asbestos was used in a wide variety of both industrial and domestic products, many occupations came in contact with the toxic substance. For example, since asbestos was integrated into so many plumbing and electrical materials, both plumbers and electricians have an increased risk of contracting asbestos-related disease.Firefighters also fall under this category because exposure can occur while working around older asbestos-contaminated homes. Many other occupations share a history of asbestos exposure as well, such as construction and railroad workers, auto mechanics, and machinists.
Asbestos products were widely used by every branch of the U.S. Armed Forces, mainly for insulation purposes in buildings, aircraft, and vehicles. But no other division of the Armed Forces utilized asbestos quite like the Navy, which found hundreds of uses for asbestos materials in its vessels and shipyards from the 1930s through the mid-1970s. The need to supply World War II efforts caused a spike in demand, which led to increased production among the nation's shipyards. Over the decades, thousands of shipyard workers and Navy veterans who were stationed aboard the contaminated vessels were heavily exposed to asbestos, often in small places with little to no ventilation. For these reasons, veterans and shipyard workers have an elevated risk of developing an asbestos-related disease.
While most accounts of asbestos exposure occur in an occupational setting, accidental exposure is another way people have come in contact with this caustic substance. For example, the World Trade Center attacks that took place on September 11, 2001 set an estimated 2,000 tons of asbestos into the air in the form of a fine dust. According to a 2006 Centers for Disease Control and Prevention report, an alarming 62 percent of those caught in the dust cloud are coping with respiratory problems. Another incidence of accidental exposure was caused by the costliest natural disaster in U.S. history-Hurricane Katrina. The hurricane damaged thousands of older asbestos-contaminated homes, many of which remain standing today. Nearly three years after the storm hit, the area is still struggling to restore infrastructure and prevent asbestos exposure from the remaining asbestos-laden structures
Pathophysiology
The mesothelium consists of a single layer of flattened to cuboidal cells forming the epithelial lining of the serous cavities of the body including the peritoneal, pericardial and pleural cavities. Deposition of asbestos fibers in the parenchyma of the lung may result in the penetration of the visceral pleura from where the fiber can then be carried to the pleural surface, thus leading to the development of malignant mesothelial plaques. The processes leading to the development of peritoneal mesothelioma remain unresolved, although it has been proposed that asbestos fibers from the lung are transported to the abdomen and associated organs via the lymphatic system. Additionally, asbestos fibers may be deposited in the gut after ingestion of sputum contaminated with asbestos fibers.
Risk Factors
The biggest and almost exclusively known risk factor for mesothelioma is exposure to asbestos. Those who have inhaled or ingested the toxic mineral are prime candidates for developing the disease. Even indirect exposure (known as secondary exposure) has been linked to cause mesothelioma in many instances.
Anyone who has encountered asbestos is at risk for developing mesothelioma. Asbestos and asbestos-containing products were commonly used in a wide variety of industries throughout most of the twentieth century. Some workers in those industries encountered the dangerous mineral on a daily basis, unknowingly exposing themselves to a substance that would eventually wreak havoc on their lungs.
In the past decade, more and more cases of secondary exposure to asbestos have come to light. Those subject to secondary exposure are often people who live in a household where someone else works with asbestos. These individuals usually inhale asbestos fibers brought home on the hair and clothes of other family members.
Many secondary exposure cases have been discovered in young people who sat on their father's or grandfather's lap when they came home from work. Other examples of secondary exposure have been found among those who lived near a factory that produced asbestos-containing products or near mines that harvested asbestos-laced vermiculite. While these individuals had no direct contact with the toxic mineral, the amount of asbestos dust in the air was enough to cause them to develop mesothelioma or another asbestos-related disease.
Studies have shown that smoking does not cause mesothelioma. However, those that smoke and are exposed to asbestos have a much higher chance of developing the disease. As a matter of fact, some statistics show that smokers are as much as 90 percent more likely to develop mesothelioma after being exposed to asbestos. This is an important risk factor and one that is often overlooked by long-time smokers. In addition, those who have already developed asbestosis should avoid smoking at all costs, as the combination of the two significantly raises the risk of contracting mesothelioma.
Clinical Features
Research for mesothelioma generally begins in a laboratory and initial tests typically involve lab mice. If early experiments are deemed successful and all parameters of the research meet federally-imposed guidelines for use on humans, the treatment is deemed safe for trial.
Clinical trials are designed to test new medications, treatments and therapies on patients who have a particular disease. Most oncologists, especially those who specialize in the mesothelioma treatment, will be well-versed on what clinical trials are available and can easily determine who qualifies for what trial. Patients considering participation in clinical trials should know some basic information before making their decision.
Management
There are several types of treatment available for patients with mesothelioma, some recommended more frequently than others. The most commonly used treatments are surgery, chemotherapy, and radiation therapy. In addition, some experimental treatments are becoming more widely used, or are showing some encouraging results in clinical trials. These treatments include photodynamic therapy, gene therapy, and immunotherapy, among others.
Most of these treatments are not used in isolation. In many cases, treatment may consist of a combination of therapies. For example, surgery to remove as much of the cancer as possible may be followed by radiotherapy or chemotherapy to remove residual cancer cells. This is one of the most common treatment options for mesothelioma among those who are candidates for surgery.
A number of alternative therapies can also be combined with traditional treatment options. Many patients choose to add alternative therapies such as massage, acupuncture, or TENS therapy to their conventional treatment approach in an effort to enhance or compliment the treatment process. A variety of alternative therapies, including aromatherapy, meditation, or yoga, are often added to a treatment regimen to provide pain relief and foster relaxation.
Prognosis
Mesothelioma is not generally diagnosed until the disease is its latest stages of development primarily because of the amount of time it takes for mesothelioma patients to display the symptoms associated with the disease. In many cases, mesothelioma symptoms do not appear until several decades after the initial asbestos exposure occurred. Additionally, the symptoms of mesothelioma are very general, and often resemble less serious conditions which can make the cancer difficult to diagnose. As a result, the prognosis for the majority of patients is poor, but many doctors can recommend treatment options such as surgery, chemotherapy and radiation to help combat the disease.
Doctors typically address the cancer in terms of stages , ranging from stage one to stage four, with the cancer’s progression increasing with each stage. A mesothelioma patient’s stage greatly affects their prognosis. Unfortunately, once mesothelioma cancer has reached stage three or four, treatment options not only become more limited but less effective as well. When a patient has stage four mesothelioma, the cancer has spread to other parts of the body, and tumors have often deeply penetrated organs and tissues. The poor general health of the patient often rules out the possibility of surgery.
Malignant mesothelioma is typically diagnosed in individuals over 55 years old, though there are certainly exceptions. Because of this, some patients who are diagnosed already have multiple medical problems caused by advancing age, making treatment even more difficult and increasing the mortality rate among mesothelioma patients.