In terms of cell type, mesothelioma is classified as one of three different types. The three types are epithelioid, sarcomatoid, and biphasic mesothelioma. Each of these categories is further subdivided.
Roughly half to three-quarters of all malignant mesothelioma cases are epithelioid mesothelioma. These cells have a fairly uniform shape, a unique nucleus, and a tubular pattern. They are shaped like cubes or other multi-sided structures. epitheloid mesothelioma cells occur in a protective layer of tissue that is called the epithelium. Epithelium surrounds organs like the lungs and the digestive tract. This type of malignant mesothelioma has symptoms such as chest pain, pleural effusion (fluid build-up in the layers of tissue surrounding the lungs), and shortness of breath. It is often confused with adenocarcinoma, and patients are urged to seek a second opinion if they are diagnosed with adenocarcinoma in case the disease is actually epithelioid mesothelioma.
To differentiate between adenocarcinoma and mesothelioma cancer cells, the cells are examined under electron microscopes to identify characteristics of the cells when they are chemically stained. Pathologists with experience in differentiating mesothelioma cases from adenocarcinoma cases are invaluable when it comes to properly diagnosing mesothelioma.
Asbestos inhalation
In people who develop epitheloid mesothelioma, epithelial cells are affected by asbestos fibers inhaled by the person. Over a period of up to 50 years the asbestos fibers work through the lung wall into the mesothelium and eventually to the membrane lining the chest wall. The consequence of pleural effusion, which causes pressure on the lungs and shortness of breath is often what sends mesothelioma patients to doctors for diagnosis.
Epithelioid mesothelioma is usually treated with a multi-pronged approach. The specifics of treatment are dictated by how advanced the cancer is, and how old and otherwise healthy the patient is. If surgery is an option, then a surgeon will remove parts of the mesothelium that have been invaded by the epithelioid cells and may remove part of the lung, or all of the lung too.
Though adenocarcinoma and mesothelioma are sometimes confused, they are two different diseases. While adenocarcinoma is found in the mesothelium, it doesn’t start in the mesothelium, while mesothelioma does start in the mesothelium. Adenocarcinoma starts in inner epithelium of an organ. Adenocarcinoma can spread to the mesothelium or the pleural spaces around the lung. Because epitheloid mesothelioma can also show up in the pleural spaces, the two different types of cancer, mesothelioma and adenocarcinoma, can easily be confused. Not only that, but the cells of both types of cancer look similar, and chemical staining of both types of cells show similar results.
Symptoms of mseothelioma
Symptoms, which often affect older people, include pleural effusions, chest pain, and trouble breathing with either adenocarcinoma or epithelioid mesothelioma. These are the reasons why it is important to have an expert pathologist who has experience in diagnosing mesothelioma working on the diagnosis, and why second opinions are so important.
Mesothelioma survival rates for epitheloid mesothelioma are not good, and one main reason for this is that it can take decades to produce symptoms, by which times the disease is often quite advanced. The earlier in the course of the disease that a diagnosis is made, the better the mesothelioma prognosis.
Sarcomatoid mesothelioma
The second type of mesothelioma, sarcaomatoid mesothelioma, can also be confused with other cancer types. The cells in this type of cancer have irregular oval shapes and the cells often resemble those in sarcomatoid carcinoma, which only rarely occurs in the lungs. Sarcomatoid mesothelioma only accounts for 10 to 15% of all mesothelioma cases. It is the least common form of malignant mesothelioma, making up only 7% to 20% of mesothelioma cases.
With sarcomatoid mesothelioma, the nuclei of the cells are harder to detect under the electron microscope than the nuclei of mesothelioma that is epithelioid in type. With sarcomatoid mesothelioma, the cells look spindle-like and elongated, and the cells often overlap and are oddly shaped. Sarcomatoid mesothelioma cells are easily confused with sarcomatoid carcinoma as well as a disease called sarcoma, and so it is best to have a second pathology opinion from a pathologist who specializes in diagnosing mesothelioma.
Sarcomatoid mesothelioma is more likely to be peritoneal mesothelioma than pleural (lung) mesothelioma or pericardial (heart) mesothelioma. It is not easy to differentiate sarcomatoid mesothelioma cells from other types of sarcomas found in the abdominal cavity and in the lungs. But generally speaking, sarcomatoid mesothelioma cells are more oddly-shaped than epitheliod cells, and they often can be seen in mitotic stages, which are the various stages of the cells splitting and reproducing by mitosis.
Mesothelioma of the lung is often spread across the mesothelial surface, rather than being concentrated in a tumor. This is another clue that can help pathologists identify sarcomatoid mesothelioma rather than another type of cancer. The cells of sarcomatoid mesothelioma respond to different treatments than the cells in epithelial mesothelioma. Sarcomatoid cells may resist the chemotherapy drugs that attack proteins in epithelioid cells. Treating sarcomatoid mesothelioma is considered to be more difficult than treating epithelioid mesothelioma. Whether this is truly the case or whether pure sarcomatoid mesothelioma cases are so rare is a matter of conjecture.
Sarcomatoid cells are more aggressive cancer cells than epithelioid cells are. Sarcomatoid cancer tends to move faster, and the mesothelioma prognosis is somewhat worse for a patient with this type of mesothelioma compared with epitheloid mesothelioma. Sarcomatoid is more resistant to treatment than epithelial mesothelioma. The treatments include new options such as immunotherapy, gene therapy, photodynamic therapy, intensely modulated radiation therapy, and the development of new chemotherapy drugs. On the other hand, other types of mesothelioma are treated with more traditional combinations of treatments like chemotherapy, surgery, and radiation therapy.
The appearance of the sarcomatoid mesothelioma cells is similar to types of cancers appearing in other body parts, like the kidney. It is rare in the lungs. Less than 1.3% of lung cancers ar e sarcomatoid cancers. The disease most commonly confused with sarcomatoid mesothelioma is pulmonary sarcomatoid carcinoma. Sarcomatoid tumors are more common in men by four times, and are associated with smoking. The symptoms of both types of disease are similar, too, with chest pain, fluid around the lungs, and difficulty breathing being typical of both types of disease.
High-grade sarcoma
Another disease that may be confused with sarcomatoid mesothelioma is high-grade sarcoma. Sarcomas arise in cartilage, bone, fat, or muscle, while carcinomas affect the epithelium. Sarcoma that has spread to the surface of the lungs can be hard to differentiate from sarcomatoid mesothelioma.
Sarcomatoid mesothelioma accounts for only about 10 to 15 percent of the mesothelioma cancer cells and it is the least common form of mesothelioma.
Sarcomatoid cells are typically oval shaped, but more irregular. The nucleus of sarcomatoid cells is not as clearly visible under an electron microscope as the nuclei of epithelioid mesothelioma cancer cells. Because the irregular oval shape is a common among cancer cells, sarcomatoid mesothelioma can be confused with sarcomatoid carcinoma and with sarcoma.
Biphasic mesothelioma
It is more common to find sarcomatoid cells and epithetlial cells together in some combination. This is the third type of mesothelioma, called biphasic mesothelioma. Biphasic disease has been diagnosed more often over the last decade, possibly because the aging of the population of people who spent many years working with asbestos means many more of them are being diagnosed. Currently, biphasic cells are being seen in around half of all mesothelioma cases.
Biphasic cells are a combination of sarcomatoid and epithelioid cells. There is no distinct cellular type, but a combination of the types of cells seen in the other two types. Biphasic mesothelioma is easier to diagnose and harder to confuse with other types of cancers than sarcomatoid and epithelioid versions of the disease. To put it more simply, a person is diagnosed with biphasic mesothelioma when he or she is found to have both epithelioid and sarcomatoid mesothelioma at the same time.
Like the other types, biphasic mesothelioma is due to asbestos exposure. It may result in the patient having malignant epithelial cells in one part of the pleural membrane and malignant sarcomatoid cells in another part. In general, the two subtypes are found in different parts of the tumor rather than just being mixed together. Unfortunately, when epithelioid and sarcomatoid cells are separated, the type of mesothelioma can be misdiagnosed. That is why it is very important that surgeons taking tissue samples for a biopsy take multiple tissue samples, so that if both types of cancer cells are present, the doctors will know to treat both types of the cancer.
Mesothelioma treatments are similar for the three types of malignant mesothelioma. The prognosis associated with each type is different, however, and so is the mesothelioma survival rate for each kind. The average mesothelioma survival rate for biphasic mesothelioma is six months, which is the shortest for the three types of the disease. Because of this, many biphasic mesothelioma cancer patients are more willing to undergo radical or experimental treatments for their disease than are patients with epithelial or sarcomatoid mesothelioma.
Anyone who has had asbestos exposure on the job, or from sharing a household with people who worked with asbestos products, should be certain that his or her physician knows about this asbestos exposure so that any suspicious symptoms can be followed up quickly to get the earliest diagnosis possible in the event of mesothelioma. Early diagnosis is one of the most important factors in a good mesothelioma survival rate.