Mesothelioma is a rare form of cancer that arises in the mesothelium, a thin membrane that protects your internal organs and allows them to move freely without damage-causing friction. You have several of these membranes in your body: the pleura surround the lungs; the peritoneum protects your abdominal cavity (stomach, intestines, and other organs); and the pericardium envelops your heart.

Mesothelioma can occur in any of these membranes, but pleural mesothelioma is by far the most common, accounting for about 70 percent of all mesothelioma cases. Although some people may have a genetic predisposition for developing mesothelioma, nearly all cases arise from exposure to asbestos. Men typically are at greater risk than women, but women also get this disease.

This chapter provides an overview of mesothelioma, starting with a look at who’s at risk for developing mesothelioma, how your respiratory system works and how mesothelioma affects your body. Look for cross-references to other chapters for more detailed information.

Who’s at Risk

Between 2,500 and 3,000 new cases of mesothelioma are diagnosed each year. Anyone who has been exposed to asbestos is at risk for developing mesothelioma, and, although your risk increases with the length of time you were exposed to asbestos, even small exposures to asbestos can cause mesothelioma.

Ironically, your risk also increases with the length of time that elapses after your exposure to asbestos. Mesothelioma has a very long latency period – that is, the period between exposure to asbestos and the onset of symptoms of the disease.
Mesothelioma typically doesn’t appear until at least a decade after asbestos exposure; in some cases, the latency period has been 50 years or longer.

Sometimes, mesothelioma results from exposure to naturally occurring asbestos, but the most common causes are exposure to asbestos in the workplace or from products used in the home (see Chapter 2 for examples of such products). Spouses and family members of workers also may have been exposed to asbestos dust and fibers from the clothing the workers wore home from the job site.

Here are some quick facts about mesothelioma and risk factors:

• Men are more commonly diagnosed than women, because men more typically worked in jobs where they were exposed to asbestos. These high-risk jobs include electricians, shipyard workers, factory workers, pipefitters, oil refinery workers, auto mechanics, machinists, and steel workers. (See Chapter 2 for more on how asbestos was used and the most dangerous jobs relating to asbestos exposure.) Older men account for more than 90 percent of all new mesothelioma diagnoses each year. Although no one knows exactly why, Caucasian men are statistically more likely to develop the disease than African-American or Hispanic men.
• Women who worked in factories had increased direct exposure to asbestos and are more likely to be diagnosed with mesothelioma later in life.
• Women whose husbands, fathers, or other household members worked in high-exposure jobs also are at risk of developing mesothelioma from secondary exposure to the asbestos dust and fibers on work clothes. Children in these homes also are at risk from secondary exposure.
• People who used asbestos-containing products in their homes are at increased risk of developing mesothelioma.
• Because of mesothelioma’s long latency period, people over the age of 50 are more likely to be diagnosed with the disease. Most mesothelioma diagnoses come in patients between the ages of 50 and 70; those who are diagnosed earlier may have a better chance of long-term survival.
• People serving as first responders – fire-fighters, police officers, rescue workers and recovery personnel – may be exposed to asbestos at disaster sites, such as the World Trade Center.
• Armed service personnel, especially those serving on ships in the Navy or Coast Guard, also are at higher risk of developing mesothelioma.

How Your Respiratory System Works

Your respiratory system takes in oxygen and releases carbon dioxide, while filtering the air you take in to remove irritants and to control temperature and moisture levels. To accomplish all this, your respiratory system consists of several parts (see Figure 1-1):

• The epiglottis – a small flap of tissue that prevents food and liquid from going into your lungs when you swallow. When you breathe, the epiglottis opens to allow air into your trachea or windpipe, the main airway into your lungs.
• Your right lung has three lobes, and your left lung has two (to accommodate the heart). Each lobe is surrounded by a thin membrane called a pleura, which contains a small amount of fluid to prevent friction while you breathe. Another pleura covers each whole lung to prevent friction between your lungs and your chest wall.
• Bronchi are the large airways that branch off from your trachea into your lungs. Each bronchus feeds into several smaller airways called bronchioles that reach deep into your lungs, much like a tree spreads out from the main trunk into progressively smaller branches. (Together, the bronchi and bronchioles are often referred to as bronchial tubes.)
• Each bronchiole ends in a little bunch of air sacs called alveoli, which transfer oxygen into your blood stream and absorb carbon dioxide for you to expel when you exhale.
• Air filtration elements include the hairs in your nose, which trap particles of dust, pollen and other irritants, and the cilia, or tiny hairs, that line your bronchial tubes.
  The cilia are like little brooms, moving back and forth to sweep mucus out of the airways so you can cough it out. Mucus is like a mop, gathering up irritants and germs to keep them from invading your body.

Your diaphragm, the muscle that separates your chest cavity from your abdominal cavity, also is involved in helping you breathe.

Asbestos causes problems because its fibers are extremely fragile and break easily into tiny particles that your body’s air filtration system can’t trap and expel. The longer you’re exposed to asbestos dust, the more likely these fibers are to work their way through your airways and into your body. Even single exposures to small amounts of asbestos can cause mesothelioma. (See Chapter 2 for more details on what asbestos is and what it has been used for.) When asbestos gets into your lungs and stays there, it can cause mesothelioma – which often isn’t diagnosed until 10 or more years after your exposure to asbestos dust and particles.

Figure 1-1: Your respiratory system

Types of Mesothelioma

Mesothelioma can be either benign, meaning it doesn’t grow and spread, or malignant, meaning it grows and invades surrounding tissue. Malignant mesothelioma is the most serious of all asbestos-related diseases and can be extremely difficult to diagnose and treat (see Chapter 3).

There are four types of mesothelioma:

• Pleural mesothelioma occurs in the membranes, or pleura, surrounding the lungs and the lobes of the lungs. Unlike most cancers, malignant pleural mesothelioma doesn’t form a single tumor; instead, it spreads through the pleura like a sheet of water. Symptoms of early-stage mesothelioma are typically quite mild and often lead to misdiagnoses (see Chapter 3). You may experience chronic (ongoing) pain in one area of the chest, weight loss or fever; some patients have difficulty breathing because of fluid build-up that prevents the lungs from expanding freely. Malignant pleural mesothelioma can – and often does – spread to other parts of the body, including the brain.Because pleural mesothelioma is difficult to diagnose in its early, more treatable stages and very difficult to treat in its advanced stages, survival rates are low. Fewer than one in ten patients with malignant pleural mesothelioma live three to five years beyond their initial diagnosis.
• Peritoneal mesothelioma occurs in the membranes of the abdominal cavity and frequently spreads to the liver, intestines and other organs. Patients with this form of the disease typically report severe abdominal pain, as well as difficulty with bowel movements, nausea and vomiting, swollen feet and fever. One-year survival rates for peritoneal mesothelioma are a bit better than for the pleural variety, but more than half of these patients survive less than a year following the onset of symptoms.
• Pericardial mesothelioma, which invades the protective sac that surrounds the heart, makes up only about two percent of all cases of this disease. As the disease progresses, it interferes with the heart’s ability to pump oxygen-rich blood through your body, which in turns causes a rapid decline in overall health. Symptoms of pericardial mesothelioma are similar to those of a heart attack: pain in the chest, shortness of breath and nausea.
• Testicular mesothelioma attacks the lining of a testicle. Like pericardial mesothelioma, this form of the disease accounts for only about 2 percent of all cases, but it has the best survival rates; more than half of testicular mesothelioma patients live two years or more after their initial diagnosis.

Mesothelioma Stages and Cell Types

Several factors play a role in treating mesothelioma and in survival rates for this disease, including your age and overall health. But two of the most critical factors in determining which treatments are effective are the stage of the disease and its cell type.

Most forms of cancer are categorized as Stage 0, Stage I, Stage II, Stage III or Stage IV. Stage 0 is cancer that is localized; it hasn’t spread to surrounding tissues. Stages I through III indicate more extensive disease; the tumor is large, for example, or cancer cells have spread to nearby lymph nodes and/or organs next to the location of the primary cancer site. Stage IV is cancer that has spread (or metastasized) to another organ, typically relatively far from the original cancer site.

Depending on your doctor and treatment center, you may run across different staging methods and labels. In general, though, localized mesothelioma is considered Stage 0 or Stage I. Advanced mesothelioma means the cancer has spread.

Treatment options and survival rates are almost always better when mesothelioma is caught in its early stages. However, because symptoms can easily be mistaken for other ailments
(see Chapter 3), mesothelioma often isn’t diagnosed until it has progressed to surrounding tissues and organs.

Mesothelioma’s cell type, or histology, also presents treatment challenges. Some mesothelioma cells come from the lining of membranes, or epithelial, layers. These epithelial cancer cells are well-differentiated and have a distinct elongated shape, sort of like mud bricks (see Figure 1-2). Epithelial mesothelioma is the most easily treated and makes up between 50 percent and 75 percent of all mesothelioma diagnoses.

Sarcomatoid mesothelioma involves cells from bone and muscle. These cells are basically oval in shape, but they’re more irregular than epithelial cells. Sarcomatoid mesothelioma is less common than the epithelial variety, accounting for between 7 percent and 20 percent of annual diagnoses.

Biphasic mesothelioma includes both epithelial and sarcomatoid cancer cells. Treatment options for both sarcomatoid and biphasic mesothelioma are more challenging because the sarcomatoid cells come from muscle and bone, and it’s difficult to destroy the cancerous cells without also damaging or destroying healthy cells. Epithelial mesothelioma also tends to respond better to treatment, so one-year survival rates typically are much better for patients with epithelial mesothelioma.

Figure 1-2: Biphasic, sarcomatoid and epithelial mesothelioma cells

Other Asbestos-Related Lung Diseases

Exposure to asbestos can lead to other lung problems besides mesothelioma. Asbestosis is scarring of the lung tissue as a result of inhaling the microscopic fibers in asbestos dust. These fibers can penetrate deep into your lungs and lodge in the tiniest bronchioles and air sacs. When your body detects these foreign invaders, it launches its immune response, deploying specialized cells to try to destroy the fibers. However, because asbestos is resistant to the chemical processes your immune system uses, your body’s second defense is to lay down fibrous tissue over the invader to prevent it from spreading. This fibrous tissue eventually encapsulates the asbestos fiber, creating a mass that can obstruct the small airways in your lungs and thicken the walls of the air sacs, which in turn interferes with their ability to infuse your blood with oxygen and remove carbon dioxide. As more of this scar tissue develops, your lungs become unable to expand and contract, and breathing becomes difficult.

About half of all people who are exposed to asbestos over a prolonged period develop pleural plaques, localized areas of scar tissue that forms around asbestos fibers. Most pleural plaques are found in the pleura lining the diaphragm (the parietal pleura), but they occasionally occur in the pleura near the ribcage. Unlike asbestosis, pleural plaques apparently stop forming when you’re no longer exposed to asbestos. However, depending on your exposure level, pleural plaques also can make breathing difficult – often two decades or more after you were exposed to asbestos.

Pleural plaques are non-cancerous and cannot become malignant. However, patients with pleural plaques often also develop asbestosis or malignant mesothelioma. Nearly all patients with asbestosis, and many with malignant mesothelioma, also have pleural plaques.

Lung cancer – that is, cancer that forms inside the lung tissue, rather than in the lining around the lungs – often goes hand-in- hand with mesothelioma. Although most people associate lung cancer with smoking, nonsmokers who have been exposed to asbestos are as much as six times more likely to develop lung cancer than nonsmokers who have never been exposed to asbestos. And, just as mesothelioma has a long latency period, asbestos-related lung cancer usually isn’t diagnosed until at least 15 years after exposure to asbestos.

Smoking does not increase your risk of developing mesothelioma. However, your doctor will advise quitting smoking to prevent additional damage to your lungs (and most doctors advise quitting regardless of whether you have any lung disease).