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A mesothelioma tumor is a rare type of cancer caused by exposure to asbestos. Mesothelioma tumors have unique characteristics, such as small nodules, and can be classified by location, cell type, and stage. Mesothelioma is an aggressive cancer with a poor prognosis.
What Is a Mesothelioma Tumor?
A mesothelioma tumor is a malignant growth that usually develops after years of past asbestos exposure. Unlike other solid tumors, mesothelioma tumors grow as multiple, small nodules.
Mesothelioma tumors develop in the mesothelium, a double layer of tissue that surrounds the lungs, abdominal organs, heart, and testes. They are aggressive and spread rapidly.
Characteristics of Mesothelioma Tumors
- Rather than forming one large tumor, mesothelioma develops as many small nodules.
- The nodules of mesothelioma eventually coalesce into larger masses. In pleural mesothelioma, these come together in the later stages to form a rind around the lung.
- The tumors usually begin forming in the lower chest cavity.
- Other sites of mesothelioma tumors are in the peritoneum of the abdominal cavity, the pericardium around the heart, and around the testicles.
- Pleural mesothelioma tumors often invade the pericardium around the heart, the diaphragm, the surface of the lung, the chest wall, the mediastinum, and along tracts used to drain fluid.
Types of Mesothelioma Tumors by Location
All types of mesothelioma tumors have these unique characteristics, but they can also be classified by where they first form. Mesothelioma is a cancer of the mesothelium, a thin, double-layer of tissue that surrounds organs in the body. There are four areas in which mesothelioma tumors may form:
- Pleural mesothelioma. More than three-quarters of cases of mesothelioma form in the pleural tissue around the lungs. The main cause of this type is the inhalation of asbestos fibers.
- Peritoneal mesothelioma. Most of the remaining diagnoses are peritoneal mesothelioma, tumors that arise in the mesothelial tissue in the abdominal cavity. Asbestos exposure also accounts for most cases of peritoneal mesothelioma, either through inhalation and migration of fibers in the body or ingestion.
- Pericardial mesothelioma. Very rare are tumors that begin in the pericardial tissue around the heart. Experts in mesothelioma still do not fully understand how asbestos fibers migrate to the pericardium.
- Testicular mesothelioma. The rarest of all types arise from tumors in the tissue surrounding one or both testicles. There are very few reported cases of this mesothelioma, which may or may not be related to asbestos.
Mesothelioma Tumors by Cell Type
The tumors can also be categorized by the majority of the cells in them. A diagnosis of mesothelioma includes a designation of cell type because this informs prognosis and treatment. There are three main tumors by cell type:
- Epithelioid. When most of the cells in the tumor are epithelial in nature, it is considered epithelioid mesothelioma. These account for more than half of diagnoses and are easier to treat because the tumor cells adhere to each other to some extent. The cells are cuboid, oval, or polygonal in shape.
- Sarcomatoid. Spindle-shaped, fibrous cells in the tumor are known as sarcomatoid. Between 10% and 20% of cases are diagnosed as this type. It comes with a worse prognosis and is difficult to treat as compared to epithelioid tumors. The sarcomatoid cells tend to detach and spread more readily.
- Biphasic. The remainder of diagnoses, 20% to 30%, are tumors with a mix of epithelioid and sarcomatoid cells.
Mesothelioma tumors may also contain rare subtypes of the above cell types: lymphohistiocytoid, tubulopapillary, glandular, adenomatoid, and others.
What Are the Symptoms of Mesothelioma Tumors?
Mesothelioma symptoms depend on the location of the tumors. Pleural mesothelioma tumors usually cause:
- Shortness of breath
- Chest pains
Peritoneal cancer symptoms include:
- Abdominal pain
- Abdominal swelling and fluid buildup
- Gastrointestinal distress
Pericardial mesothelioma causes symptoms similar to the pleural form. All types of mesothelioma cause fatigue, weight loss, and fever as they progress to the later stages. When they metastasize, the tumors cause symptoms in other parts of the body.
Mesothelioma Tumors and Genetics
Asbestos is the number one risk factor for mesothelioma, but research in recent years proves that genetics play a role as well. For instance, many people with mesothelioma have a mutation in the BAP1 gene, a tumor suppressor gene. With the mutation, the gene does not activate and slow or stop the growth of tumors.
Other suppressor genes that may be involved in the development of mesothelioma tumors include NF2 and CDKN2A. These genetic connections may explain why asbestos causes mesothelioma in some people, but many others can be exposed to the fibers without ever developing tumors.
Mesothelioma tumors are difficult to diagnose for several reasons. They are rare and they cause symptoms similar to more common conditions. They also resemble other types of cancer, like lung cancer.
Oncologists use several types of imaging scans to diagnose cancer. CT scans are typically most useful in finding mesothelioma tumors. These images help oncologists identify abnormal growths, but they cannot confirm a mesothelioma diagnosis.
CT scans lead oncologists to the right area to take a biopsy, a tissue sample. Pathologists then look at the sample under a microscope to identify malignancy, cell type, and tumor type.
Mesothelioma Tumor Markers
Even with a biopsy, identifying a tumor as mesothelioma is challenging. Recent research has led to the identification of numerous tumor markers for mesothelioma. There is no single identifying marker, but important ones include mesothelin, fibulin-3, osteopontin, and calretinin.
Staging Mesothelioma Tumors
Tumors are classified by stage of development, using the TNM system. Mesothelioma tumors that remain small and located in one area or only on the pleural tissue are classified as stage 1. Once the tumors have penetrated the chest wall, diaphragm, lung, or lymph nodes it has developed to stage 2.
Most cases of mesothelioma are diagnosed in the later stages. At stage 3, tumors have penetrated deep into the chest wall, the pericardium, multiple lymph nodes, and the other side of the chest. By stage IV the tumors have metastasized, meaning they have spread to more distant parts of the body.
Treatment of Mesothelioma Tumors
Some of the characteristics of these tumors, including aggressive spreading and the formation of many nodules, make them difficult to manage.
It is easier to stop the spread and remove tumor nodules in the early stages of the cancer. During these tumor stages, surgery is a typical treatment, often followed by chemotherapy.
For later stages of tumor development, there may be too much mass to remove surgically. In these cases, chemotherapy is the primary line of treatment with the aim of extending life but not curing the cancer.
Are Mesothelioma Tumors Curable?
Unfortunately, mesothelioma cancer is not curable. There are rare cases of patients achieving remission, but this is only possible if the cancer is diagnosed in the very early stages.
What Is the Life Expectancy of a Person with Mesothelioma?
Mesothelioma tumors are unique and notoriously difficult to diagnose and treat. Being able to remove or eliminate all the small growths is usually impossible, and the prognosis for a mesothelioma tumor diagnosis is not good for most patients.
Life expectancy for mesothelioma cancer varies depending on the stage at diagnosis, type, treatment choices, and more. Considering all types, the average life expectancy for a person with mesothelioma is 12 to 21 months.
A diagnosis of mesothelioma tumors is difficult to take. Because it is so strongly associated with asbestos, you should report any past exposure to your doctor. You might be a good candidate for early screenings.Get Your FREE Mesothelioma Packet
Page Medically Reviewed and Edited by Anne Courtney, AOCNP, DNP
Anne Courtney has a Doctor of Nursing Practice degree and is an Advanced Oncology Certified Nurse Practitioner. She has years of oncology experience working with patients with malignant mesothelioma, as well as other types of cancer. Dr. Courtney currently works at University of Texas LIVESTRONG Cancer Institutes.