Most people who have heard of malignant mesothelioma know of it as a lung disease that occurs in people who work or have worked with asbestos. While it is in most cases a rare form of cancer that grows in the layer of tissue covering the lungs, the layer of tissue known as the mesothelium actually covers most internal organs, and the mesothelium can develop cancer in places other than around the lungs, including the heart, the abdomen, and the testicles. According to the American Cancer Society, mesothelioma is diagnosed in 2,000 to 3,000 people per year in the U.S. Mesothelioma survival rates are historically low, though improvements are being made in cases of earlier diagnosis.
Pleural (lung) mesothelioma causes symptoms such as painful breathing (also called pleurisy), shortness of breath, coughing, chest pain, weight loss, and lumps of tissue under the skin of the chest. When it attacks the mesothelium in the abdomen, a form of the disease known as peritoneal mesothelioma, symptoms include swelling of the abdomen, pain, altered bowel habits, weight loss, and lumps of tissue in the abdominal area. In the tissue layer over the heart, mesothelioma can cause chest pain and difficulty breathing. Mesothelioma of the testicles is so rare that little information is available about the symptoms.
Another rare form of the disease is misleadingly known as “benign mesothelioma.” It occurs in a different type of cell than typical mesothelioma and can be very aggressive. Physicians now refer to this type of the disease as “solitary fibrous tumor.” It usually has no symptoms and is found when looking for other conditions. Solitary fibrous tumors are not linked to exposure to asbestos. Mesothelioma survival rates for this version of the disease are higher than for traditional pleural mesothelioma.
Mesothelioma is a risk for anyone who works around asbestos fibers. When asbestos breaks apart, like when it is mined or when asbestos insulation is removed, the dust that is created may be inhaled (causing pleural mesothelioma) or swallowed (causing peritoneal mesothelioma). How the asbestos fibers cause the cell mutations that lead to cancer is not understood, but it may be the result of the asbestos irritating the tissues of the mesothelium.
Unfortunately, pleural mesothelioma is usually not diagnosed until it is well advanced and causes symptoms. This is the main reason for mesothelioma survival rates being low. In addition to difficulty breathing, difficulty swallowing, and chest pain, it can put pressure on the superior vena cava, the large vein leading from the upper body to the heart and can press on the nerves and spinal cord, causing pain. It can also cause fluid to accumulate in the chest, compressing the lungs and making breathing labored. People who die of mesothelioma are usually killed by complications like heart failure, lung failure, or stroke.
The mesothelioma survival rate looks particularly bleak because the disease is not usually diagnosed until it is advanced enough to cause symptoms. At that point, mesothelioma treatment options are very limited. Generally speaking, from 7 to 20% of mesothelioma patients will survive for five years or more after being diagnosed. The average survival for someone with mesothelioma is between four and 18 months after being diagnosed. Symptoms can take as long as 50 years to develop after exposure to asbestos, so most people with mesothelioma don’t know that they have it.
Because of this, development of new tests and aids to earlier diagnosis are important areas of research into mesothelioma. The relatively recent Mesomark blood test is able to help some people be diagnosed earlier than they would otherwise, making more mesothelioma treatment options available and improving survival rates.
Pleural mesothelioma is the commonest form of the disease. More than two-thirds of all mesothelioma cases are of the lungs. The pleura, the lining of the chest and abdominal cavity, is made up of two layers of tissue, the parietal and visceral pleura. Parietal pleura lines the diaphragm and chest wall, and the visceral pleura lines the lungs. Normally these two layers of membrane have enough fluid between them so that they can slip against each other as breathing causes the lungs to expand and then contract.
But when asbestos fibers work their way into the pleura, an unknown chemical reaction causes cellular mutations that can develop into cancer. Once these mutated cells begin to divide, the pleura thickens and more fluid can accumulate. Thickening of the pleura gradually compresses the breathing space, resulting in shortness of breath, which is one of the first symptoms people with pleural mesothelioma notice. When the fluid shows up on X-rays, doctors refer to it generically as “pleural effusion,” and it is a symptom for diseases other than mesothelioma. That is why it is critical that doctors who see pleural effusion on an X-ray know whether the patient has been exposed to asbestos in the past.
Pleural mesothelioma is what is known as “dose-dependent,” which means that the longer you were exposed to asbestos, or the heavier the exposure to it, the greater the chances of developing mesothelioma (whether of the lungs or another type). The dose dependency also affects the length of time between exposure and diagnosis, which can range from 10 to 50 years. Because even doctors have a hard time diagnosing mesothelioma sometimes, it is vital for anyone who has been exposed to asbestos to bring symptoms like shortness of breath to the attention of their doctor promptly. The earlier the diagnosis of pleural mesothelioma, the greater the mesothelioma survival rate.
The peritoneal version of mesothelioma is very rare, with only 100 to 500 cases of the disease diagnosed each year in the U.S. It accounts for less than one-third of all mesothelioma cases. In the abdominal cavity, the abdominal lining is, like that of the lungs, made of two layers of membrane, the parietal and visceral peritoneum. The visceral peritoneum covers the organs and forms most of the intestinal tract’s outermost layer. Lining the abdominal cavity itself is the parietal peritoneum. As with the lungs’ pleura, a certain amount of fluid resides between the two peritoneal layers, allowing smooth movement of organs against one another, such as when the intestines move food along the digestive tract. Peritoneal mesothelioma comes from overproduction of the fluid between the layers, creating excess abdominal cavity fluid.
As with pleural mesothelioma, peritoneal mesothelioma survival rates are higher the earlier the disease is diagnosed. Also like the pleural version of the disease, the symptoms can be non-specific. That’s why anyone with abdominal swelling or pain who has been exposed to asbestos must bring this to the attention of his or her doctor. Unfortunately, most peritoneal mesothelioma diagnoses don’t come until the disease is already advanced, and the diagnosis itself takes on average four months to be made. It often takes a combination of diagnostic procedures such as lab tests and surgical biopsy before peritoneal mesothelioma is officially diagnosed.
Factors affecting the peritoneal mesothelioma survival rate include the cancer’s location in the abdomen, how much it has spread, the patient’s age, and how quickly the disease was diagnosed. Like with many types of cancer, early diagnosis improves the mesothelioma survival rate. Additionally, with peritoneal mesothelioma, it is important to find out if the disease began in the lungs, because pleural mesothelioma is more common and spreads to the peritoneal cavity sometimes.
Mesothelioma treatment options include the traditional cancer treatments of surgery, radiation, and chemotherapy. Usually two or more of these mesothelioma treatment options will be combined. A number of clinical trials in the U.S. are showing promising results, particularly for those whose mesothelioma was diagnosed relatively early. In these cases, some clinical trials are showing mesothelioma survival rates of up to 40% as opposed to the 10% or so average mesothelioma survival rate.