Straight Talk about Mesothelioma, a blog series created by Michael T. Milano, M.D., Ph.D., a radiation oncology specialist, as a resource for mesothelioma patients and their loved ones.
Many family members, friends, and caretakers ask the same question when their loved one has been diagnosed with pleural mesothelioma: “What does ‘pleural’ mean?” It’s a good question, as “pleural” isn’t a word that shows up in our everyday vernacular.
The pleura is a thin, double-layered membrane that lines the chest cavity and lungs. The cells that make up the pleural lining are known as mesothelial cells, from which the cancer’s name “mesothelioma” is derived. These cells also make up the lining of the abdominal wall, heart (and pericardium), and testis. Functionally, the pleural lining in the chest enables the lungs to expand and contract effortlessly during breathing.
What else does the pleural lining do? The pleural lining also secretes fluid that helps reduce friction of the lung surface against the chest wall. In short: this thin, 1mm-thick membrane does quite a bit – it’s vital to our health and survival.
How Does a Person’s Pleura Become Cancerous?
Cancer of the pleura’s mesothelial cells is known as “malignant mesothelioma.” The most common site for the development of mesothelioma is the pleura, followed by the abdomen and the covering of the heart (called the pericardium).
How does a person’s mesothelial cells become cancerous? The only known cause for mesothelioma is prior exposure to asbestos, a naturally-occurring mineral fiber that, for decades, was used extensively as a fire-retardant by many manufacturers. It has been found that the majority of individuals who develop mesothelioma have a history exposure to asbestos, most commonly through work.
A significant number of people exposed to asbestos worked in the mining industry where they may have either inhaled and/or ingested asbestos fibers. Even the act of washing the clothes of an individual who works or has worked with asbestos carries a risk for development of mesothelioma. Much more rarely, causes of mesothelioma have been linked to inhalation of fibrous silicates such as talc, another natural mineral which is often “tainted” with asbestos fibers, as the two are often found together in nature.
What is the Process of Asbestos Entering the Body and Causing Cancer?
When the asbestos fibers are inhaled, a large portion of the fibers get trapped in the lower parts of the person’s lung. Because of this, mesothelioma most commonly starts along the base of a person’s chest. As the cancer grows, it spreads to the lungs, diaphragm, and the outer lining of the heart. Even though it is largely known that asbestos is the only known cause of mesothelioma, exactly how asbestos causes the deadly cancer is not well understood by scientists and doctors. Some doctors and researchers believe that the fibers force genetic changes in cells, which then gradually causes cells to become cancerous.
Once exposure to asbestos fibers has occurred, there is a long latency period for mesothelioma to present itself. This period may vary from 20 to 50 years and is almost never less than 10 years. Scientists and doctors know that the asbestos fibers somehow settle in the pleura and then begin a mild inflammatory process. The thin pleural lining starts to become thicker in certain areas and, in some cases, this may also be associated with fluid accumulation in the chest cavity (a condition known as “pleural effusion”).
During the early stages, mesothelioma cells grow extremely slowly and may show up as small bumps (called “nodules”) on the pleura – which is why many mesothelioma patients do not have any symptoms early on in the cancer’s development. With time, the nodules fuse and the pleura becomes thicker. Gradually the affected pleura starts to trap and restrict mobility of the lung and diaphragm. As the cancerous tumor grows, it spreads along the pleura and invades the diaphragm, adjacent to the heart and chest wall.
How Does One Find out if They Have Pleural Mesothelioma?
Common symptoms of mesothelioma include varying degrees of shortness of breath, dry cough, and chest pain. The diagnosis of a mesothelioma is at first very difficult because the symptoms are often non-specific to this one type of cancer and the tiny bumps (or “nodules” as they’re known to doctors) are rarely visible – even on a standard chest x-ray. A more certain diagnosis can usually be made by a pleural biopsy, although an abnormality must first be seen on an x-ray or computerized tomography (CT) scan to guide where to biopsy. Unfortunately for many patients who have the above symptoms and are then diagnosed with mesothelioma, the tumor has usually invaded other nearby tissues and is incurable.
Although asbestos is highly regulated in the U.S. by the Food and Drug Administration (FDA) and the Occupational Safety and Health Administration (OSHA), there are still thousands of people being diagnosed every year – roughly 3,200 Americans – from having been exposed much earlier in life.
To put such a trend into a more global perspective, over the past decade in Western Europe, despite a ban on asbestos, more than 20,000-30,000 deaths per year have occurred in Europe and by the year 2030, the numbers, according to the European Economic and Social Committee (EESC), are expected to reach over 300,000.