Epithelioid mesothelioma is the most common cell subtype of asbestos-caused cancer.
Key Points about Epithelioid Mesothelioma
- The epithelioid cell type accounts for the majority (70%) of mesothelioma cases and is the most treatable.
- Epithelioid mesothelioma cells grow and spread predominantly by local expansion into surrounding tissue and organs.
- Treatment usually includes a combination of radical surgery, pemetrexed and cisplatin chemotherapy, and radiation therapy (trimodal therapy).
- Response to treatment and median survival for epithelioid mesothelioma is the best of the 3 cell types, generally between 18 and 24 months. More than 80% of patients live beyond 12 months.
Mesothelial cells are a normal, specialized type of epithelial cell that form the membranes that line the chest cavity and all of its contents, including the lungs. Mesothelioma is so named because it results from the mutation of normal mesothelial cells into cancer cells that are then able to grow and spread. The epithelioid cell type (not to be confused with normal epithelial cells) is one of two main mesothelioma cell types and a third that is a combination of the two. The epithelioid form is the most common mesothelioma cell type, usually accounting for as many as 70% of all cases.
Epithelioid Cell Characteristics
- Elongated oval, tubular, or egg-shaped with visible nuclei
- Fast division and tumor growth, but slow metastasis because of their tendency to stick together
- More common in pleural mesothelioma than peritoneal mesothelioma
- Spread mostly to nearby lymph nodes
The human body contains normal epithelial tissue and cells which are responsible for things like protection, sensory perception, and fluid secretion. The structure of these cells varies depending on location in the body. When these cells mutate into cancer cells, they are called epithelioid cells. The epithelioid cell type is so named because the mesothelioma cells have similar appearance to the epithelial cell line from which mesothelial cells develop. Under the microscope they typically appear square to slightly elongated and the nucleus is readily visible. These cells tend to clump together as they spread and, compared to other cell types, are less likely to metastasize. Mesothelioma epithelioid cells must be tested carefully since they may resemble other serious malignancies in the chest, especially breast, lung, and metastatic cancer of the colon.
Epithelioid Cell Mesothelioma Has Five Subtypes
There are a number of epithelioid cell subtypes that have different physical characteristics, meaning they may also respond differently to certain treatments. Subtypes include:
- Adenoid — This subtype may be found in all types of mesothelioma and may also mimic other tumors, making diagnosis difficult.
- Small Cell — Common in peritoneal mesothelioma patients, this cell subtype has distinct shape patterns, can be mistaken for small cell lung cancer, and is notoriously difficult to treat.
- Cystic — This subtype is rare and usually found in peritoneal mesothelioma patients, more commonly in women than in men.
- Papillary — A less aggressive subtype, papillary cell mesothelioma is rare and also usually found in the peritoneum.
- Deciduoid — Rarely found in pleural mesothelioma, deciduoid cells are found in 50% of peritoneal mesothelioma cases.
Diagnosis of Epithelioid Cell Mesothelioma
The epithelioid cell type resembles cell types found in other cancers, including adenocarcinoma and breast cancer. Symptoms of epithelioid mesothelioma may include:
- Shortness of breath
- Chest pain or tightness
- Fluid buildup (pleural effusion)
For diagnosis, a doctor will use radiology or pathology exams to look for malignant mesothelioma cells. When a radiological evaluation and/or laboratory test identifies or is suspicious for mesothelioma, an evaluation of tumor tissue is performed and the doctor may ask about any history of asbestos exposure. A sample of the tumor is usually obtained by a biopsy.
Immunochemistry Is The Only Way To Definitively Diagnose Mesothelioma
By examining the malignant cells in the laboratory, mesothelioma in general, and an epithelioid cell type specifically, can be distinguished from other tumors. A typical tumor cell evaluation includes both microscopic examination and molecular testing of the cells in a process called immunohistochemistry. Immunohistochemistry is a method used to identify molecular “footprints” characteristic of a specific cancer cell or cell type, and is the basis for many of the new approaches to treatment. This is also the only way to definitively diagnose mesothelioma.
Multimodal Treatment Is Recommended For Epithelioid Cell Mesothelioma
Since epithelioid cells respond very well to treatment, most patients with epithelioid mesothelioma are candidates for aggressive treatment, except those with very advanced tumors or poor performance status. Performance status is a scale that reflects a patient’s overall health and wellbeing, as well as the ability to conduct activities of daily life. Treatment of this cell type is usually multimodal and includes:
- Curative Surgery — One of the types of radical surgery, usually performed with the goal to remove all visible tumor.
- Radiation therapy (radiotherapy) — Administered to reduce the amount of remaining tumor.
- Chemotherapy — Given before (neoadjuvant) or following (adjuvant) surgery. Presently, the drugs used most often are pemetrexed and cisplatin in combination.
Prognosis Depends on Multiple Factors
Studies suggest that trimodal combination therapy for patients with epithelioid mesothelioma is more effective than supportive care. In one study, supportive care included radiation therapy, and was part of all treatment categories (chemotherapy, surgery, and trimodal). Patients receiving only supportive care had the worst outcomes, with median survival around 6 months.
Patients who had either chemotherapy or surgery added to their treatment regimen had better survival times compared to supportive care only, but did not fare as well as those who received both chemotherapy and surgery plus radiation therapy (trimodal group).
Drug combination chemotherapy with pemetrexed and cisplatin also has been shown to be superior to cisplatin alone. Median survival specific to this cell type, using trimodal therapy, is generally reported in the 18-24 month range. Thus, there is a benefit from more aggressive treatment plans for those patients with the epithelioid cell type who are judged to be in suitable health.
The overall response to therapy and the prognosis for epithelioid mesothelioma are considerably better compared to the other major cell types. One study showed that 60% of epithelioid patients who received treatment survived at least a year after the beginning of treatment. The number of patients with the epithelioid cell cell type surviving beyond 40 months is consistently better compared to the non-epithelioid (sarcomatoid and mixed) forms.
Nuclear Grading Is Used to Classify Epithelioid Cells
|Epithelioid Nuclear Grade||Median patient survival|
|Grade 1||28 months|
|Grade 2||14 months|
|Grade 3||5 months|
Another recently proposed method to further classify epithelioid mesothelioma cells is referred to as nuclear grading. The nucleus of the cell is “command central”. It contains the cell’s genes, which control almost all cell activities such as synthesis of many molecules including enzymes and hormones, cell metabolism and growth rates and cell reproduction and lifespan. Grading is done by a score that is based on specific abnormalities of the nuclei of mesothelioma cancer cells. These scores, graded as low, intermediate, or high, are significantly associated with patient outcomes. If validated by other investigators, nuclear grading shows promise as an alternative or complementary way to assess mesothelioma cells.