Pleural Mesothelioma and Lung Cancer
Pleural mesothelioma and lung cancer are separate cancers caused by asbestos exposure. These cancers originate in different locations, yet cause similar symptoms like chest pain and difficulty breathing. Similar tools are used to diagnose the cancers, but treatment plans differ.
Once asbestos is inhaled, it can become lodged in lung tissue or in the lining of the lungs (known as the pleural lining) and can cause cancer in both locations. Asbestos lodged in lung tissue causes lung cancer (LC), while asbestos lodged in the pleural lining causes pleural mesothelioma (PM).
Pleural mesothelioma is not considered a form of lung cancer because it does not originate in lung tissue. However, PM is sometimes misdiagnosed as lung cancer, most commonly adenocarcinoma or a rare form known as pseudomesotheliomatous lung cancer.
Though surgery, chemotherapy and radiation therapy are used to treat both cancers, the types of surgeries, chemotherapy drugs and radiation therapy plans differ. The prognosis for PM and LC is comparable for the first year following diagnosis, but LC patients have better long-term survival.
Both are Caused by Asbestos
All forms of asbestos, including amphibole and serpentine forms, are known to cause lung cancer and pleural mesothelioma. Amphibole forms of asbestos (including amosite, crocidolite, tremolite and anthophyllite) are more carcinogenic than serpentine asbestos (chrysotile).
Regardless of the type of asbestos someone is exposed to, scientists know that significantly less asbestos exposure is required to cause pleural mesothelioma than lung cancer. The reason for this difference is unknown, but some researchers suspect genetic susceptibility could play a role.
Following asbestos exposure, both PM and LC exhibit a long latency period before the cancers develop. The average latency for pleural mesothelioma is 30 to 50 years, while lung cancer’s latency is shorter, at 10 to 20 years.
Smoking Doesn’t Increase Risk of Pleural Mesothelioma
Asbestos exposure alone can cause both PM and LC, and smoking alone can cause lung cancer. However, smoking alone cannot cause pleural mesothelioma, nor does smoking increase the risk of PM in those with asbestos exposure.
Studies prove that the combination of smoking and asbestos exposure can increase the risk of lung cancer by 50-fold. Conversely, research proves that smoking does not affect the risk of developing pleural mesothelioma at all. Because the toxic combination increases the risk of lung cancer so dramatically, there are about twice as many cases of asbestos-related lung cancer in comparison to pleural mesothelioma.
Also worth noting is the fact that lung cancer risk decreases after smoking cessation, but the risk of pleural mesothelioma only increases with age. The body cannot recover from asbestos exposure the way it can from cigarette exposure, and because asbestos fibers can become trapped in bodily tissues indefinitely, ongoing damage can carry on for decades. The risk of lung cancer may decrease with time and smoking cessation, but the risk of mesothelioma continues to increase.
Diagnostic Tools are Similar
Doctors use similar diagnostic tools to diagnose these cancers. X-rays, other imaging scans, bronchoscopy or a biopsy are used to diagnose and differentiate pleural mesothelioma from lung cancer.
X-rays and various imaging scans (such as CT or PET scans) help doctors to identify suspicious masses near the lungs. A bronchoscopy involves the insertion of a tube down the throat into the large airways to check for abnormal growth. A biopsy involves the collection of a tissue sample with a long needle or a minor surgery. Biopsy collection techniques can vary depending upon which cancer is suspected.
If lung cancer is suspected, doctors will perform a sputum cytology test. This diagnostic test requires the patient to cough up a sample of phlegm, which is then tested for abnormalities.
Pathologists use various tests to distinguish PM from LC and other cancers. Certain biological markers, such as proteins or antibodies, help pathologists tell the cancers apart on a cellular level. Markers such as calretinin, cytokeratin and Ber-EP4 assist in deciphering PM from adenocarcinoma and other lung cancers.
Treatment Plans Differ
Common treatment options for PM and LC are the same as for other cancers (surgery, chemotherapy and radiation therapy). However, the types of surgeries, chemotherapy plans and radiation techniques used to treat PM and LC will vary. Different combinations of conventional treatments, known as multimodal therapy, are used for each cancer and largely depend upon the stage of the tumor and the overall health of the patient.
Surgeries for lung cancer will attempt to remove either a portion of the affected lung, a lobe or the whole lung. Pleural mesothelioma surgeries may involve the removal of the pleural lining, a portion of the lung or the entire affected lung. Certain palliative surgeries, such as a pleurodesis, may be used in advanced cases of either cancer.
Some of the same chemotherapy drugs treat PM and LC, but not all are used on both, and the dose will depend upon which cancer a patient has, as well as the stage of the tumor. Cisplatin and pemetrexed are the most common chemotherapeutic agents used for pleural mesothelioma, while docetaxel, vinorelbine and paclitaxel are common for lung cancer. Some chemotherapy drugs, such as cisplatin, carboplatin, pemetrexed and gemcitabine, are used for both cancers.
Radiation therapy is difficult to administer to either cancer because of the proximity of the lungs to vital organs like the heart and spinal cord. When administered alone, radiation aims to ease pain in both PM and LC patients, but cannot and does not intend to cure these cancers. When combined with other treatments, especially following aggressive surgery, radiation therapy can reduce local tumor recurrence in PM and LC. Radiation has also been used in PM along tracts created by biopsies, chest tubes and surgical incisions to prevent tumor seeding, or local metastasis along the incision. Tumor seeding is rare in lung cancer.
Photodynamic therapy has been used to treat both PM and LC, but is more commonly administered to lung cancer patients. Other novel treatments, such as immunotherapy and gene therapy, are experimentally used for each cancer with limited success thus far. Complementary and alternative medicine is available for both cancers, and can ease symptoms and reduce side effects of conventional treatments.
Prognosis Diverges after One Year
The prognosis for PM and LC is similar one year after diagnosis: Survival rates for pleural mesothelioma and lung cancer are 38 percent and 42 percent, respectively. At the five-year mark, 16 percent of lung cancer patients and 5 to 10 percent of pleural mesothelioma patients are alive.
When the cancers are diagnosed early, survival rates significantly improve. When lung cancer is diagnosed while the tumor is localized, the five-year survival rate is approximately 53 percent. In one pleural mesothelioma study conducted at Brigham and Women’s Hospital, 46 percent of patients with stage I disease survived beyond five years. (These patients all had an epithelial cell type and successful surgeries that cleared nearly all tumor cells.)
Despite some similarities, pleural mesothelioma and lung cancer are separate conditions that require different treatment plans to extend survival. It is important for patients with either cancer to work with a specialist who can offer expertise in the latest available treatments.