Mesotheliomas are a rare kind of cancer that affect the lining of certain internal organs and body cavities. The vast majority of mesotheliomas are caused by exposure to asbestos. There are 4 types of mesotheliomas according to their location: pleural, pericardial, peritoneal, and testicular. The 2 most common are pleural and peritoneal. Mesotheliomas can also be classified into either malignant or benign, with the former being more serious. And lastly, mesotheliomas can be classified according to their cell types: epithelial, sarcomatoid, and biphasic. Sarcomatoid is the most aggressive type of mesothelioma cell.
Pleural mesotheliomas account for 3 out of 4 mesothelioma cases. It is primarily caused by exposure to friable asbestos which is asbestos that becomes airborne and is then inhaled into the lungs. The microfibers of asbestos get lodged in the lining of the lungs, known as the pleura, where they initiate molecular damage to the chromosomes found in cells. This gravely disrupts mitotic division resulting in abnormal progeny cells or daughter cells. Over time, these defective progeny cells initiate neoplastic proliferation until such time that a tumor is evident.
The clinical manifestations of pleural mesothelioma include shortness of breath, dry cough, blood-tinged sputum, lower back pain, and painful breathing. In some cases, there may also be difficulty swallowing, lumps under the skin of the chest, unexplained weight loss, night sweats, and fatigue. Diagnosing pleural mesothelioma starts with a careful examination of the patient’s health history. Exposure to asbestos warrants diagnostic testing with x-rays, CT-scans, or MRIs to show changes in the structure of the lungs. Biopsy and cytology confirms the results of the diagnostic imaging examinations.
Mesotheliomas do not have a good prognosis. Pleural mesotheliomas are generally given a prognosis of about 10 to 12 months often depending on the histologic cell type involved. If the cell type involved is sarcomatoid, prognosis may even be as short as 6 months. Nevertheless, chemotherapy remains the treatment of choice as it can add up to several more months to the prognosis. Surgery and radiation therapy produce highly variable results.
As much as 20 percent of all mesothelioma cases are of the peritoneal type. There are two schools of thought regarding the pathogenesis of peritoneal mesotheliomas. The first is by way of inhalation of asbestos particles. These diffuse into the lymph and are drained in the peritoneum. The second is by way of ingestion of asbestos-containing food or the swallowing of asbestos microfibers. These travel down the digestive tract and diffuse into the peritoneum.
The manifestations of peritoneal mesothelioma include abdominal pain, changes in the bowel movement, feeling of fullness, nausea and vomiting, and abdominal swelling. Some of the cardinal signs of cancer such as night sweats, fatigue, and unexplained weight loss may also be present. Diagnosis requires both imaging and histologic and cytologic examinations as confirmatory tests.
Among the mesotheliomas, peritoneal mesotheliomas have the best prognosis. 1 out of 4 peritoneal mesothelioma patients have been shown to survive as long as 3 years but only with early diagnosis and treatment. The treatment of choice for peritoneal mesothelioma is heated intraperitoneal chemotherapy although surgery, radiation therapy, and chemotherapy remain excellent options.
Cancers can be classified whether they have the tendency to metastasize or not. Malignant cancers such as malignant mesotheliomas are more difficult to treat because it is extremely difficult to determine which part of the body the cancer cells have already migrated to. Removing the primary tumor does not necessarily mean that there are no longer any cancer cells in the body. Additionally, the edges of the malignant tumor are highly irregular such that surgically removing the tumor is a challenge. This is different from benign cancers where the borders are more defined.
Malignant mesotheliomas are thus very serious cancers that affect the mesothelial lining of certain body organs and cavities, particularly the lungs, the heart, the abdomen, and the testes. On the average, 5 percent of all malignant mesothelioma cases can have a prognosis of 5 years.
Seven to 20 percent of mesothelioma cases are classified as belonging to the Sarcomatoid cell type. This histological cell type of mesothelioma is the most resistant to cancer treatments and is often described as the most aggressive of all cell types of mesotheliomas. These sarcomatoid mesothelioma cells are found in 10 to 20 percent of all pleural mesotheliomas and no more than 4 percent of peritoneal mesotheliomas. What makes the diagnosis of sarcomatoid mesothelioma challenging is that it can mimic other types of cancers. Nevertheless, histologic studies of biopsy samples reveal sarcomatoid tumors as giant, spindle-shaped cells that are clumped in fibrous bundles.
The symptoms associated with sarcomatoid mesothelioma are dependent on the location of mesothelioma. If it is located in the pleura, manifestations are often respiratory in origin. If it is located in the peritoneum then abdominal and gastric problems will be the major manifestations. Treatment is dependent on the staging of the mesothelioma with chemotherapy often offering a better prognosis than surgery and radiation therapy. Doxorubicin combined with selenite has been shown to be a promising chemotherapeutic modality. Other possible combinations include cyclophosphamide, adriamycin, dacarbazine, and vincristine.