Mesothelioma is cancer of the membrane that forms the lining of several body cavities. The mesothelium is composed of two layers of cells: An inner layer called the visceral membrane that immediately surrounds the organ and an outer layer called the parietal layer. The mesothelium produces a lubricating fluid between these layers, allowing moving organs (such as the beating heart and the expanding and contracting lungs) to glide against adjacent structures. In some people, genetic mutations occur within cells, causing them to multiply out of control. When this happens in mesothelium cells, the result is mesothelioma, an aggressive but rare form of cancer.
Types of Mesothelioma
There are four types of mesothelioma. All are rare – only about 3,000 new cases of mesothelioma are diagnosed every year.
Pleural mesothelioma affects the lung cavity, or pleura. It’s the most common type of the disease, accounting for about three-quarters of all cases, according to the Mesothelioma Research Foundation of America. Because it’s relatively rare compared to illnesses with similar symptoms, such as lung cancer and viral pneumonia, pleural mesothelioma may be misdiagnosed. Symptoms include chronic chest pain, shortness of breath, chronic coughing, weight loss and fever.
Peritoneal mesothelioma is the second most-common type of malignant mesothelioma, accounting for 10 to 20 percent of all cases. It attacks the peritoneum, the mesothelial tissue that covers most of the organs in the abdominal cavity. Symptoms include weight loss, abdominal pain and swelling, bowel obstruction, blood clotting abnormalities, anemia and fever.
Pericardial mesothelioma affects the heart sac, or pericardium. It’s very rare – only about 150 cases have ever been reported. While it can occur at any age, it’s most often diagnosed in people in the fourth to seventh decades of life, and men are twice as likely as women to be afflicted. Symptoms include chest pain, fluid buildup around the heart, a mass in the space between the lungs, abnormal or difficult breathing, chronic coughing and irregular heartbeat.
Mesothelioma of the tunica vaginalis testis
The least common type of the disease is mesothelioma of the tunica vaginalis testis (also called paratesticular mesothelioma), which affects the mesothelial lining around the testes. Fewer than 100 cases have ever been reported. Symptoms include a hydrocele (a fluid-filled sac attached to a testis) or hernia. The main treatment is orchidectomy – removal of the affected testis.
Diagnosis and Treatment
The American Cancer Society says the average age at the time of diagnosis for pleural mesothelioma, the most common and most studied form of the disease, is 69. Mesothelioma has a long dormancy period – it may be 10 to 40 years between the time a patient was exposed to a carcinogen and the time symptoms develop. However, once mesothelioma develops, it grows and spreads quickly.
Because mesothelioma is so rare, doctors often suspect other diseases with similar symptoms. To diagnose mesothelioma, doctors may use chest X-rays, echocardiograms, CT and PET scans and MRI. They also perform a biopsy – surgical removal of tissue to be examined by a pathologist.
Doctors can treat mesothelioma, but most cases do not result in a cure. Traditional treatments include chemotherapy, radiation therapy and surgery. Doctors will often use chemotherapy or radiotherapy to stunt the growth of a tumor before attempting surgery. Unfortunately, mesothelioma generally manifests as small and even microscopic nodules within the mesothelium, so surgery is unlikely to remove all cancerous cells. Doctors may use further chemotherapy or radiotherapy after surgery to attempt to kill any remaining cancer.
Doctors can also provide palliative treatment for mesothelioma – that is, treatment designed to manage the pain and symptoms of the disease. Two palliative procedures for pleural mesothelioma are thoracentesis and pleurodesis. Thoracentesis is an outpatient procedure in which a doctor drains the buildup of fluid in the membranes around the lungs, which are called pleural effusions. Pleurodesis aims to prevent pleural effusions. After draining excess fluid, surgeons install an irritant inside the pleural space that creates inflammation and permanently obliterates the pleural space. This procedure requires several days’ stay in a hospital. After some short-term discomfort during recovery, the patient should have less pain on a daily basis. If patients are experiencing chest pains due to a buildup of fluid around the heart, doctors can perform pericardiocentesis, an outpatient procedure to remove fluid from the pericardial sac. Patients with peritoneal mesothelioma may experience fluid buildups similar to pleural effusions, but in the peritoneal cavity. These buildups – called ascites – can be drained in an outpatient procedure called paracentesis.
Nearly all cases of mesothelioma are malignant, which means they can metastasize, or spread to other locations. However, some people develop a solitary fibrous tumor of the pleura, peritoneum or other part of the mesothelium – called solitary because it grows as a single lump, in contrast to the smaller nodules that characterize malignant mesothelioma. These tumors can generally be cured by surgical removal.
The Role of Asbestos in Mesothelioma
Mesothelioma is a rare cancer. Asbestos exposure is the main cause of pleural mesothelioma, though most people exposed to asbestos, even in large amounts, do not get the disease. Contributing factors include a personal history of asbestos exposure, living with someone who worked with asbestos and a family history of mesothelioma.
The federal government began banning asbestos for various uses in 1973, after it became clear that exposure to asbestos could result in serious respiratory conditions. Yet asbestos is still approved for many uses. In construction work, shipbuilding and home renovation, microscopic asbestos fibers are released into the air, where they can remain airborne for hours. If fibers are breathed in, they become trapped in the lining of the lungs and can remain there for the rest of the person’s life. The fibers can cause scarring and genetic changes in body cells that lead to pleural mesothelioma. If the fibers are ingested, they can penetrate the lining of the abdomen, leading to peritoneal mesothelioma. Workers in industries and areas where asbestos is used may be repeatedly exposed to asbestos fibers – and they can carry fibers home on their hair, skin and clothes, exposing their families. To pay for the cost of mesothelioma treatment, many patients and their families filed lawsuits against manufacturers of the asbestos products related to their exposure.
When the mesothelioma lawsuits began pouring in, asbestos manufacturers were forced to set aside billions of dollars to settle the barrage of claims. By the early 2000s, nearly a million lawsuits were filed.
Buckling under the weight of liability claims, many manufacturers filled bankruptcy and set up trusts to compensate mesothelioma patients.
Staging and Life Expectancy
Doctors rate pleural mesothelioma in four stages – I, II, III, and IV – depending on how far the cancer has spread. To determine the stage for any particular patient, doctors look at the spread of the primary tumor, the presence of cancer in nearby lymph nodes and metastasis to other organs. Median survival rate of pleural mesothelioma varies according to the patient’s stage, as shown in this table created by the American Cancer Society. Staging information is not available for other forms of mesothelioma because they are rare and not well-studied.
Factors linked to longer life expectancy include being younger, being female, being able to carry out normal tasks of daily life, and having no chest pain or weight loss.