Types of Mesothelioma
There are four main types of mesothelioma, with the most common forms affecting the lining of the lungs or abdominal cavity. Each type indicates the area of the body where the cancer originates. Additionally, doctors may examine the cellular features of a mesothelioma tumor to learn important characteristics of the disease. This allows them to determine the cancer’s histological type, which is useful to know before starting treatment.
When mesothelioma begins to develop, tumors form on the mesothelial lining surrounding the lungs, abdomen, heart or testicles. These types of mesothelioma are known as pleural, peritoneal, pericardial and testicular mesothelioma. While the majority of mesothelioma tumors are malignant, there are also noncancerous forms of the disease, known as benign mesotheliomas.
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The percentage of cases diagnosed for each major types of mesothelioma is represented below.
Pleural Mesothelioma
Pleural mesothelioma develops in the mesothelial lining of the lungs, known as the pleura. Approximately 75 percent of all mesothelioma cases are of the pleural type. Although symptoms may vary, the most common pleural mesothelioma symptoms include:
Treatment for pleural mesothelioma largely depends on the stage of the cancer. In early diagnosed cases, potentially curative surgery may be an option for patients. Most treatments are palliative and aim to relieve symptoms and improve quality of life.
Peritoneal Mesothelioma
Peritoneal mesothelioma develops in the mesothelial lining of the abdomen, known as the peritoneum. Approximately 20 percent of all mesothelioma diagnoses are of the peritoneal type and symptoms typically include:
Patients with peritoneal mesothelioma may note symptoms that result from the thickening of the peritoneal membrane and the build-up of fluid. Because peritoneal mesothelioma metastasizes more quickly than other types of mesothelioma, treatment may be difficult.
Pericardial Mesothelioma
Pericardial mesothelioma develops on the exterior lining of the heart, known as the pericardium. These types of mesothelioma is rare and accounts for about 5 percent of all mesothelioma cases. Symptoms develop when fluid builds up in the spaces between the layers of the pericardial membrane and may include:
As with other types of mesothelioma, pericardial mesothelioma is most commonly treated with palliative measures. Surgical removal of pericardial tumors is risky because of the close proximity to the heart.
Testicular Mesothelioma
Testicular mesothelioma affects the lining of the testes. Less than 1 percent of mesothelioma cases are made up of these types of mesothelioma and many patients are diagnosed while receiving surgery or treatment for another condition. Because of the rarity of the disease, it has been difficult for medical researchers to develop a comprehensive list of symptoms. The two main indicators of this cancer are thought to be testicular lumps and swelling of the scrotum. These types mesothelioma is usually not diagnosed until lumps develop.
Testicular mesothelioma patients may undergo a surgery to remove all or part of the affected testicle. Adjuvant therapy may be recommended, in which case the patient will also obtain chemotherapy or radiation therapy to kill any remaining cancer cells.
Histological Subtypes of Mesothelioma
One way that doctors can further describe a mesothelioma tumor is by examining the type and structure of its cells. Although it is most common for doctors to classify this cancer based on the tumor’s location, there are also various histological subtypes of pleural, peritoneal, pericardial and testicular mesothelioma.
With the study of cellular anatomy, known as histology, doctors can identify the features of a mesothelioma tumor’s cells and determine its unique histological subtype. With this information, they can better predict the patient’s disease progression, survival time and likely response to treatment.
While many rare histological sub types of mesothelioma exist, the three most common cell types are epithelial, sarcomatoid and biphasic.
Epithelial Mesothelioma
Accounting for 50 to 70 percent of all cases, epithelial mesothelioma is by far the most common histological subtype. Compared to other cell types of mesothelioma, epithelial mesothelioma typically responds better to treatment. It is therefore the histological subtype associated with the best survival.
Sarcomatoid Mesothelioma
The least common of the three major histological subtypes, sarcomatoid mesothelioma is observed in about 10 to 20 percent of all cases. Because this subtype is particularly aggressive, survival is usually poor. In one of the largest sarcomatoid mesothelioma studies to date, the median survival time was 3.5 months.
Biphasic Mesothelioma
A combination of epithelial and sarcomatoid cells within one tumor, biphasic mesothelioma occurs in about 20 to 35 percent of cases. Because the ratio of epithelial to biphasic cells can vary significantly from case to case, the distribution of cells influences survival. A greater number of epithelial cells is generally associated with a better prognosis.
Malignant Versus Benign Mesothelioma
The majority of mesothelioma tumors are malignant, which means the disease is cancerous and has the ability to spread to other locations throughout the body. But not all tumors are malignant. Some mesothelioma tumors are benign, or noncancerous. These tumors grow slowly and cannot metastasize to distant organs.
Benign mesotheliomas usually develop in the peritoneums of patients with no history of asbestos exposure. Although most patients are young to middle-aged women, doctors have observed benign cases in men as well. Several complications can arise if a tumor grows large enough, but most patients experience no symptoms at all. 20 percent of patients with benign mesotheliomas larger than 7 cm experience painful swelling of the joints and bones, low blood sugar, comas and seizures.
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