Pleural mesothelioma affects the lining of the lungs and is the most common form of cancer caused by asbestos.
Key Points about Pleural Mesothelioma
- Exposure to asbestos is the only scientifically verified cause of pleural mesothelioma.
- Diagnosing pleural mesothelioma can be extremely difficult, since the symptoms may look like those of other diseases.
- While prognosis is generally poor, early detection is the single best way to improve the chances of survival.
- The most common treatment is a combination of surgery, radiation therapy, and chemotherapy (i.e., multimodal therapy).
Pleural mesothelioma is a type of cancer that affects the linings of the lungs (the pleura). Caused by exposure to asbestos, pleural mesothelioma is the most common of the three types of mesothelioma, with more than 75% of all cases affecting the pleura.
Asbestos Triggers Mesothelioma in the Pleura
The pleura is a sac of soft tissue that encompasses the lungs. It is lined with a thin membrane known as the mesothelium, which secretes a vital fluid that allows the lungs to expand and contract. When the mesothelium of the pleura becomes damaged, it can cause problems breathing and, ultimately, lead to death.
The primary cause of pleural mesothelioma is exposure to asbestos. Asbestos fibers are long, thin and sharp, and they often have hooks or curls that can cause them to become embedded in the pleura upon being inhaled. Over time, these sharp fibers irritate the mesothelium and lead to chronic inflammation and scar tissue.
In individuals who are heavily exposed to asbestos, these fibers can trigger an uncontrollable growth of cancerous cells in the pleura, eventually forming tumors. This is a very slow process, which usually takes several decades before it becomes detectable. The 20 – 50 year latency period between exposure and onset of the disease accounts for the poor prognosis associated with pleural mesothelioma.
Following a diagnosis, patients usually exhibit multiple tumor masses. The surface of the pleura closer to the lung (known as the parietal surface) is often more affected than the surface further away from the lung (visceral surface). The right lung, which is typically larger, often suffers more damage than the smaller left lung. More asbestos tends to settle in the lower lungs than the upper lungs.
Once multiple tumors begin to form, they can often grow quickly in size and can cover the entire lung cavity, making it very difficult to breathe and causing severe pain. In the advanced stages of pleural mesothelioma, the cancer may spread, or metastasize, to other nearby organs, including the heart, abdomen, and lymph nodes.
How Many People Get Pleural Mesothelioma?
In the U.S., approximately 3,000 people are diagnosed with of mesothelioma each year, with almost 90 percent of those cases developing in the pleura. About 4 out of every 5 mesothelioma victims in America are older men who worked in industrial jobs. Shipyards and mines are two of the most common types of job sites where asbestos exposure occurs.
According to a 2012 epidemiological study, globally the percentage of men who develop mesothelioma is a little bit lower, at about 73 percent. In reality, the actual percentage can vary significantly from country to country. In developing nations, the number of women and children who develop pleural mesothelioma may be greater, as they make up a larger percentage of the workforce handling asbestos regularly. However, many developing countries do not keep accurate records, so the actual number of cases is harder to determine.
In locations where asbestos occurs naturally, there is often a higher percentage of women and children who develop the disease as well. Children and adults who do not work in industrial jobs can also develop pleural mesothelioma due to second-hand asbestos exposure from products or materials used in buildings, such as schools.
Symptoms of Pleural Mesothelioma
Pleural mesothelioma is difficult to diagnose because the symptoms of the disease often resemble those of other, more common illnesses, including the flu, a cold, laryngitis, pneumonia, or whooping cough.
The first symptoms of pleural mesothelioma include shortness of breath and chest pain, caused by the growing tumors that enlarge the pleural space and cause it to fill with too much fluid. Additional symptoms include difficulty swallowing (dysphagia), short breath (dyspnea), and coughing up blood (hemoptysis). Additionally, the discomfort caused by these symptoms can lead to a loss of appetite, weight loss, and fatigue.
The chest pain caused by pleural mesothelioma is often mistaken for heart problems. Many yet-to-be-diagnosed mesothelioma victims believe they are having a heart attack or suffering from heart disease. To further complicate diagnosis, symptoms don’t usually develop until stages III or IV of the cancer.
Common Symptoms of Pleural Mesothelioma
- Chest or lower back pain
- Persistent coughing
- Coughing up blood (hemoptysis)
- Difficulty swallowing (dysphagia)
- Shortness of breath (dyspnea)
- Fluid around the lungs (pleural effusion)
- Hoarseness or difficulty speaking
- Blood clots (less common)
Diagnosis Is Extremely Difficult
Pleural Mesothelioma Diagnosis Techniques
- Chest X-rays are used to detect pleural effusions.
- CT Scans help physicians detect evidence of asbestos exposure.
- PET scans may reveal where the cancer has spread.
- Thoracentesis allow doctors to sample pleural fluid.
- Biopsies are used to collect pleural tissue samples.
It often takes weeks or even months before a diagnosis of pleural mesothelioma is made. Also, because the disease’s long latency period, past exposure to asbestos often doesn’t come to mind when patients provide a medical history. Finally, a number of other lung and respiratory diseases have similar symptoms as pleural mesothelioma, making a correct diagnosis even more challenging.
Ultimately, a definitive diagnosis of malignant pleural mesothelioma can be made only through a combination of imaging techniques and a study of the cell structure (histology) after taking a biopsy.
X-rays, CT scans, MRIs, and PET scans are the four types of imaging techniques that can be used to initially detect mesothelioma. Each of these techniques offers different capabilities and levels of resolution. Typically, the diagnosing doctor will look at scans to rule out other diseases, as well as to reveal the presence of pleural effusion. However, image scans alone are not enough to make a positive diagnosis of pleural mesothelioma.
A study of tumor cells extracted through a biopsy is the only way to confirm a mesothelioma diagnosis. For pleural mesothelioma, biopsies can be taken in the following ways:
- Thoracoscopy or pleuroscopy: A small tube with a camera is inserted into the pleural cavity to view the tumor.
- Thoracentesis: A needle is used to withdraw tumor cells from the pleura.
- Thoracotomy: An incision is made in the chest to obtain a sample from a tumor.
Once the biopsy is performed, the collected tissue is examined under a microscope to determine its cell structure (histology). If the cells are positively identified as mesothelioma, the next step is to develop a treatment plan.
Because pleural mesothelioma is so difficult to diagnose, the disease is most often in an advanced stage when discovered. That makes mesothelioma treatment options limited. Common treatment options for pleural mesothelioma include:
- Multimodal (combination)
Only a handful of pleural mesothelioma patients are candidates for surgery to remove tumors, since the tumors are often large and widespread by the time of diagnosis. If the oncologist thinks the removal of part or all of a lung would benefit the patient, surgical resection may be an option.
If surgery is included in the treatment plan for pleural mesothelioma, it will take one of two forms:
- Pleurectomy/decortication (P/D): The tumor and diseased pleura are removed.
- Extrapleural pneumonectomy (EPP): The pleura, affected lung, diaphragm, and pericardium are removed.
Pleural mesothelioma patients are often treated with one or more forms of chemotherapy. Chemotherapy involves the use of drugs that destroy fast-growing cells in an effort to shrink tumors. Despite the development of new chemotherapy drugs over the years, the success rate of treating pleural mesothelioma with chemotherapy alone is low. A number of clinical trials are attempting to find a combination of chemotherapy drugs (known as a “cocktail”) that will cure pleural mesothelioma.
Radiation therapy is another form of treatment that attempts to kill cancer cells and reduce tumor size. For pleural mesothelioma, an external source is used to bombard the lungs and pleura with radiation. However, as with chemotherapy, radiation therapy is usually not a successful treatment on its own. Most often it is used as a palliative option to help manage symptoms of pleural mesothelioma.
Some doctors opt for what is commonly known as multimodal therapy, which is a combination of two or more of the treatments described above. Most experts agree that a multimodal approach provides the best chances of survival. Recent research has also prompted experimentation with different combinations of chemotherapy drugs, resulting in positive outcomes when certain ones are used together.
Maintaining a Healthy Lifestyle During Therapy
It is extremely important for pleural mesothelioma patients to maintain a healthy lifestyle throughout the course of their treatment to combat the disease. This includes proper diet, exercise, and resting properly. Engaging in stress-reducing activities such as meditation, yoga, and tai chi have been shown in some cases to help reduce the side effects of treatments and may even boost the effectiveness of therapies.
Pleural Mesothelioma Prognosis Factors
- Patient’s age and gender
- Stage of disease when diagnosed
- Patient’s history of smoking
- Presence of pain when breathing
All forms of mesothelioma have low survival rates, and the prognosis for pleural mesothelioma is a little lower than the second-most common type (peritoneal mesothelioma). Even so, the prognosis for each individual depends heavily on a variety of factors.
As with other forms of cancer, the most important thing affecting prognosis is the stage of mesothelioma at diagnosis. If detected at an early stage, pleural mesothelioma patients tend to have a better chance at surviving beyond the average survival period. Also, patients who are in good general health at diagnosis will likely respond better to treatments than those whose health is poor.
Many other factors go into determining the prognosis, such as age, sex, and history of smoking. In general, patients who are female, do not have a history of smoking, and are under the age of 55 tend to have higher rates of survival.
Overall, the prognosis for those diagnosed with pleural mesothelioma is not good given that diagnosis often occurs in a late, advanced stage. Many patients die within six months of diagnosis; some live up to a year, but survival much beyond that length of time is rare. Clinical trials are constantly underway in hopes of discovering a cure for the disease or a way to further prolong the life of a pleural mesothelioma sufferer.