There are two basic classifications for mesothelioma cancer cells; those are epithelioid and sarcomatoid. There are sub-classifications of these cells for rare forms of mesothelioma that affect, for example, the testes; but the two designations generally define the type of mesothelioma in a diagnosis. The third possibility for cell types in mesothelioma is "biphasic," a condition in which both epithelioid and sarcomatoid cells are present.
The term epithelial refers to the cells that line both internal and external surfaces of the body. Epithelial carcinoma is cancer that begins in the cells lining an organ. The mesothelium is the membrane that lines the outer surfaces of the lungs and heart, as well as the walls of both the chest cavity and the abdominal cavity. Epithelioid mesothelioma, then, is cancer that begins in the membrane lining the outer lung surface and specifically in the cells that form the membrane. Epithelioid cancer cells are epithelial cells that have malfunctioned and begun to uncontrollably reproduce malignant cells.
Epithelioid mesothelioma, also known as epithelial mesothelioma, is the most common form of the disease; it is the primary diagnosis in well over half of all mesothelioma cases. The epithelial cells are impacted by asbestos fibers that are inhaled by the eventual cancer patient. Over a period of years – sometimes twenty or more – the asbestos fibers work their way through the wall of the lung into the mesothelium, the membrane lining the outside of the lung. Eventually the epithelioid cells may find their way to the membrane lining the chest wall.
Epithelial Cells and Cancer
Cancerous epithelial cells have a distinctive shape that can be misdiagnosed under the microscope and defined as another type of cancer known as adenocarcinoma, a form of cancer that also begins in the tissue around the lungs. The shape of epithelial cells is a flattened form that sometimes has a cubical appearance in its nucleus. Before much was known about mesothelioma and its origin in the epithelial cells, it was not uncommon for a case of epithelioid mesothelioma to be mistaken for adenocarcinoma and therefore, diagnosed as lung cancer.
Mesothelioma caused by sarcomatoid cells is much less common, which is fortunate because sarcomatoid cells are difficult to treat with chemotherapy. The general estimate is that sarcomatoid mesothelioma cases constitute 7% to 20% of all mesothelioma cases, while biphasic cases are somewhere between 20% and 35%.
Treatment of Epithelioid Mesothelioma
Treatment of epithelioid mesothelioma is generally a multi-faceted approach, the components of which are dictated by the degree to which the cancer has advanced along with the general health and age of the patient. If resection is still a possibility, a surgeon will remove sections of the mesothelium that have been impacted by epithelioid cancer cells. The surgery may include removal of all or a portion of the lung as well.
With or without surgery, treatment of mesothelioma usually calls for a combination of chemotherapy and radiotherapy; sometimes the initial radiation treatment is given during the surgical process. Slowing the progress of mesothelioma is usually chemotherapy that involves multiple drugs, attacking the malignant cells in a variety of ways. Because epithelioid mesothelioma is the most common of mesothelioma diagnoses, there is more medical history in treating this type of mesothelioma than any other.
The two chemotherapy drugs pemetrexed and cisplatin have been employed extensively with epithelioid mesothelioma treatment. Pemetrexed has shown to increase mean survival times for patients with pleural mesothelioma, compared to treatment with cisplatin alone. The role that pemetrexed plays is to interfere with the RNA and DNA synthesis in malignant epithelial cells, hindering their ability to reproduce. A singular characteristic of mesothelioma – or any other cancer – is the uncontrolled reproduction of these abnormal cells. One of the paths to slowing the spread of mesothelioma is to slow or halt the reproduction of malignant cells; epithelioid mesothelioma cells are susceptible to this approach.
A primary measurement of progress, other than improved median survival times, is the measurement of what is called the "rind" on the pleural surface. This characteristic refers to fibrotic tissue in the pleura that has hardened and grown inflexible. A hardened pleura is one of the underlying causes of the respiratory difficulties that are symptomatic of pleural mesothelioma.
For more information on the symptoms and prognosis of epithelioid mesothelioma, visit the Epithelial Mesothelioma page.
- Malignant Mesothelioma, Chahinian, et al, American Cancer Society, p.5, http://www.cancer.org/downloads/pub/docs/section28/89.pdf
- Immunohistochemistry in the Distinction between Malignant Mesothelioma and Pulmonary Adenocarcinoma, Abutaily et al, Journal of Clinical Pathology, September 2002
- Chahinian, p.6
- Phase III Study of Pemetrexed in Combination With Cisplatin Versus Cisplatin Alone in Patients With Malignant Pleural Mesothelioma, Vogelzang et al, Journal of Clinical Oncology, July 2003