Malignant Pleural Mesothelioma: A Look Into This Rare Cancer

• Malignant pleural mesothelioma may share some similarities with lung cancer, especially lung adenocarcinoma. Histopathology tests are needed to tell the two cancers apart.
• Mesothelioma is not lung cancer, even though they share many similarities.

When it comes to the unfortunate diagnosis of cancer, individuals encounter a vast array of different types. While some cancers are more widely recognized and prevalent, some belong to the category of rare and less-known forms of cancer, including mesothelioma. Although mesothelioma shares certain similarities with lung cancer, it is important to note that they are distinct diseases.

Mesothelioma is a rare cancer. The mesothelium is a membrane that lines organs in the chest, abdominal cavity and pelvis. Depending on where the malignancy (cancer) develops, the three main types of mesothelioma are:

• Pleural mesothelioma – begins in the pleura (lining of the lungs)
• Pericardial mesothelioma – begins in the pericardium (lining of the heart)
• Peritoneal mesothelioma – begins in the peritoneum (lining of the abdominal cavity)

The predominant cause of malignant pleural mesothelioma is occupational asbestos exposure, accounting for 70% of cases.

Risk factor. A single risk factor common to both types of cancers is asbestos exposure. Therefore, the states with the highest mesothelioma deaths often rank high in lung cancer deaths.

Symptoms. Many symptoms of pleural mesothelioma overlap with those of lung cancer, such as shortness of breath (dyspnea), persistent cough, difficulty swallowing, hoarseness, unexplained weight loss and fatigue.

About 14% of mesothelioma patients complain about pain in the shoulder. Some patients may also manifest swelling of the face and arms if the mesothelioma obstructs the superior vena cava.

Diagnostic methods. Diagnosing mesothelioma can be tricky. A history of asbestos exposure and chest X-ray showing pleural effusion (fluid build up in pleural/lung cavity) may raise suspicion for mesothelioma, lung cancer and other lung diseases. Doctors may order further diagnostic imaging, including contrast-enhanced computed tomography (CT) and positron emission tomography (PET). However, only biopsy and histopathology assessments can distinguish the cancer types and confirm a diagnosis. Some people may need a more invasive surgical biopsy to effectively diagnose mesothelioma.

Location. Lung tumor grows on the lung and within the lung space, while pleural mesothelioma grows on the mesothelium (the membrane that lines) around the lungs. Lung tumors are larger in size and grow in defined boundaries. Mesothelioma grows as small nodules and merges into sheath-like tumors.

Incidence rate. Pleural mesothelioma is very rare. About 3,400 cases of pleural mesothelioma are diagnosed yearly in the U.S. by estimation. On the other hand, it was estimated that 220,000 new lung cancer cases are diagnosed yearly, making it the second-most common cancer in the U.S.

Diagnosis or histopathology features. Mesothelioma and lung tumor cells have different microscopic appearances. In the pathology report, mesothelioma cells are often described as ‘epithelial,’ ‘spindled,’ or ‘sarcomatoid,’ and sometimes “mixed epithelial and spindle cell.”

The markers can distinguish mesothelioma from some lung cancer types. Immunohistochemistry (IHC) is a technique performed in the pathology process to study markers or staining patterns of different cancers. IHC markers supporting the diagnosis of malignant pleural mesothelioma are:

• Mesothelin
• D2-40 (podoplanin)
• Calretinin
• Cytokeratin (CK) 5/6
• HBME-1
• Wilms tumor-I (WT-1)

Different subtypes of lung cancer would stain positive with different sets of IHC markers.

Prognosis. Although lung cancer survival rates are similar to mesothelioma after one year from diagnosis, lung cancer patients have a better prognosis than mesothelioma patients. This may be simply because of more widespread research in lung cancer compared to mesothelioma. Thus, more treatments and specialized doctors are available for lung cancer, while mesothelioma patients have limited options to improve their prognosis.

Mesothelioma patients face a daunting path ahead of them. During this painful journey, an important step to recognize is being proactive in getting reliable information, treatment options, and the latest advancements from trusted medical professionals. Patients can then make informed decisions and actively participate in their care. By relying on medical professionals, patients can draw strength from their support and expertise, making the process less arduous. Embracing a positive mindset and seeking support from loved ones can also provide encouragement and resilience.