Characteristics and Subtypes
Epithelioid mesothelioma cells have some notable characteristics:
- They are square-shaped cells and have visible nuclei (plural for "nucleus," the center of the cell, which carries genetic material). Specialists have an easier time telling them apart from other mesothelioma cell types because of their unique appearance.
- Tumors made of epithelioid cells grow quickly. These cells replicate faster than sarcomatoid or biphasic mesothelioma tumors. However, the square shape of epithelioid cells causes them to stick together, slowing down their spread to other parts of the body.
- Epithelioid mesothelioma responds the best to treatment, because it metastasizes (spreads) slower than other cell types.
Epithelioid cells come in different shapes and sizes. Each cellular subtype responds differently to treatment. Some subtypes are more common than others, making them slightly easier to diagnose and treat.
The most common subtypes include:
- Solid mesothelial cell
The least common subtypes include:
- Clear cell
- Small cell
- Adenoid cystic
Doctors may misdiagnose these epithelioid cells cells as breast cancer and metastatic carcinomas because of similarities in cellular makeup.
Diagnosing Epithelioid Mesothelioma
Diagnosing a patient's mesothelioma cell type is the most important stage of the diagnostic process. Knowing a patient's cell type helps doctors determine the best course of treatment.
After surgeons take a biopsy of the diseased tissue, they send the sample to a pathologist. General oncologists and surgeons can make guess the diagnosis based on a patient's symptoms, but only pathologists can confirm the diagnosis and cell type. Pathologists study tissue samples under a microscope, looking for the defining characteristics of the cancerous cells.
Pathologist sometimes misdiagnose epithelioid mesothelioma as something else because epithelioid cells have similar characteristics to other types of cancer cells, such as adenocarcinoma.
Good pathologists use a thorough immunohistochemistry process help prevent a misdiagnosis. Immunohistochemistry uses special stains containing markers that help the pathologist distinguish cancer cells from one another. These stains detect specific proteins only found in epithelioid mesothelioma cells, which the pathologist can see under the microscope.
There are 4 main markers used to distinguish epithelioid mesothelioma from other types of cancer:
- Calretinin: Calretinin is a calcium-binding protein used to distinguish epithelioid mesothelioma from adenocarcinoma. A recent analysis found that calretinin showed a sensitivity of 82 percent and a specificity of 85 percent in the diagnosis of epithelioid type mesothelioma.
Sensitivity has to do with the ability of a test to determine if a patient has a disease.
Specificity has to do with the ability of a test to determine the difference between certain diseases.
- Cytokeratin 5-6:: Researchers use cytokeratin 5-6 to distinguish epithelioid mesothelioma from pulmonary adenocarcinoma. A recent study found that the diagnostic sensitivity of cytokeratin 5-6 was 83 percent. Its specificity was 85 percent.
- Wilms Tumor 1 Susceptibility Gene (WT1): WT1 is a gene that helps distinguish epithelioid mesothelioma cells from adenocarcinoma cells. It showed a sensitivity of 77 percent and a specificity of 96 percent in a number of studies.
- D2-40 (podoplanin): D2-40 is a glycoprotein that shows an increased presence in many cancers, including epithelioid mesothelioma. Specialists use it as a marker to distinguish epithelioid mesothelioma from lung adenocarcinoma. It has also been found useful in distinguishing epithelioid mesothelioma and squamous cell carcinoma.
Epithelioid Treatment Options
Epithelioid mesothelioma responds better than sarcomatoid or biphasic mesothelioma to treatment. It is less aggressive and metastasizes slower than other cell types. This means surgery is more effective for epithelioid patients because their cancer cells don't spread as quickly. Depending on the stage of a patient’s cancer, there are aggressive courses of treatment that may improve a patient’s prognosis.
Patients diagnosed with epithelioid mesothelioma may be eligible for one of the following treatment options:
Extrapleural Pneumonectomy (EPP). An extrapleural pneumonectomy is the most aggressive surgery available for a patient diagnosed with epithelioid type pleural mesothelioma. This procedure involves the removal of the entire diseased lung and pleura (protective lining of the lung). If the cancer has spread far enough, the pericardium (lining of the heart), diaphragm, and nearby lymph nodes may also be removed.
Pleurectomy with Decortication (P/D). A P/D involves the removal of the pleura (pleurectomy) and the surface layer of the lung affected by cancer (decortication). If the cancer has spread, the diaphragm and pericardium may be removed as well. About 90 percent of pleural mesothelioma patients who have this surgery experience a reduction of symptoms. The median survival rate for patients after a P/D is 20 months—a year longer than the median survival rate for mesothelioma patients as a whole.
Speaking with a mesothelioma specialist is the first step in determining the best course of treatment for a patient.
Patients diagnosed with epithelioid mesothelioma enjoy a more favorable prognosis than those with sarcomatoid or biphasic mesothelioma. The median survival time for an epithelioid mesothelioma patient is 12 to 24 months, compared with 12 months for biphasic patients and 6 months for sarcomatoid patients.
Patients with epithelioid type mesothelioma are good candidates for surgeries and emerging treatments offered through clinical trials.
If you have been diagnosed with epithelioid mesothelioma, contact a member of our Patient Help Team for more information about improving your prognosis. One of our team members can speak to you about finding the best treatment for your diagnosis.
- Guidelines for Pathologic Diagnosis of Malignant Mesothelioma: A Consensus Statement from the International Mesothelioma Interest Group. (2009). Archives of Pathology and Laboratory Medicine, 133(8). Retrieved on June 4, 2014 from: http://www.archivesofpathology.org/doi/abs/10.1043/1543-2165-133.8.1317
- Immunohistochemical Diagnosis of Epithelioid Mesothelioma: An Update. Archives of Pathology & Laboratory Medicine: November 2005, Vol. 129, No. 11, pp. 1407-1414. Retrieved on June 4, 2014 from: http://www.archivesofpathology.org/doi/full/10.1043/1543-2165(2005)129[1407:IDOEMA]2.0.CO;2
- Attanoos, R. L., & Allen, T. C. (2014). WHO Classification. Advances in surgical pathology. Philadelphia: Wolters Kluwer Health/Lippincott Williams & Wilkins.