Epithelial Mesothelioma
Epithelioid mesothelioma is the most common mesothelioma cell type, accounting for 70% of all malignant mesothelioma cases. This cell type is more commonly observed in cases of pleural mesothelioma than peritoneal mesothelioma.
What Are Epithelial Cells?
- The body is made up of different types of cells, including epithelial cells:
- The epithelial types are found throughout the body.
- They make up the tissue lining various parts of the body, including the skin, throat, blood vessels, and organs.
- These cells act as the body’s safety barrier.
- Depending on where they are located in the body, epithelial cells come in a variety of shapes but are generally flat, cube-shaped, or columnar.
- Epithelial cells are usually packed tightly together.
- Because they are so close together, cancers that develop in epithelial cells spread and metastasize more slowly, making them less aggressive cancers.
Epithelial Mesothelioma and Sub-types
When epithelial cells mutate, they may become cancerous and lose their ordered shape. A mesothelioma tumor largely comprised of mutated epithelial cells is classified as epithelial or epithelioid mesothelioma.
Pleural, peritoneal, pericardial, and testicular mesothelioma may all be epithelial. There are also several sub-types of epithelial mesothelioma cells:
- Small cell: Small cell cancers are made up of small, uniform cells. In mesothelioma, they can be easily mistaken for the cells that make up small cell lung cancer.
- Adenomatoid: These cells are both epithelial and characteristic of cells that arise in the body’s glands. Mesothelioma may be misdiagnosed as a benign adenomatoid tumor.
- Tubulopapillary: This cell sub-type forms a distinct pattern of papillary structures and small tubules and is common in mesothelioma. It may be misdiagnosed as an adenocarcinoma spread to the pleura.
- Deciduoid: This is a rare epithelial sub-type shaped like large polygons. It is easy to misdiagnose because it is so rare.
- Solid: Solid cell types may be poorly or well-differentiated. Well-differentiated solid cells are round and orderly. In the poorly differentiated type, cells are not uniform. This type may be misdiagnosed as lymphoma or large cell carcinoma.
- Cystic: Cystic mesothelioma is most common in the peritoneum and is often benign.
- Glomeruloid: These cells are round or oval-shaped and are not common in mesothelioma. They are not thought to be related to asbestos exposure.
How Is Epithelioid Mesothelioma Diagnosed?
A diagnosis of epithelioid mesothelioma begins with a physical exam. Imaging scans, including X-rays, CT scans, and MRIs, are then used to identify an unusual growth in the pleura or lungs.
A doctor will then use the scans to take a biopsy, a sample of tissue from the abnormal area.
Next, a pathologist examines physical characteristics of the cells under a microscope as well as how the cells are ordered.
This allows the growth to be identified as mesothelial or lung cancer cells.
The biopsy can also identify if the cells are epithelial or sarcomatoid. If epithelial cells are found, the pathologist will then determine which sub-type they are.
During diagnosis, it is important that you mention to your doctor any possible exposure to asbestos. Most doctors will not be looking for mesothelioma because it is rare. They will first look for other types of cancer. Informing your diagnostic team of any exposures in your past will speed the diagnosis and improve accuracy.
Immunohistochemistry in Diagnosis
There is also an innovative new technique that makes diagnosis of mesothelioma easier. Immunohistochemistry uses antibodies to detect the antigens specific to types of cancer cells.
Several of these antibodies can be used to help diagnose epithelial mesothelioma. The technique is particularly useful in differentiating between epithelial mesothelioma and adenocarcinoma.
How is Epithelioid Mesothelioma Treated?
Epithelioid mesothelioma is easier to treat than other cell types. As with any type of mesothelioma, the treatment plan depends on individual factors: age, health, preferences, cancer stage, and cancer type.
In general, epithelioid mesothelioma is treated with a multi-modal approach, utilizing two or three of the most common cancer treatments:
- Chemotherapy: Chemotherapy is used to shrink tumors before surgery or to eliminate remaining cancer cells after surgery.
- Surgery: Surgical procedures make up the bulk of treatments for epithelial mesothelioma, removing as much of the tumors as possible.
- Radiation therapy: A treatment plan may include radiation, most often after surgery to eliminate remaining cells or as a palliative procedure to shrink tumors and reduce symptoms.
Surgery for Epithelioid Mesothelioma
Epithelioid mesothelioma is generally considered a resectable type of mesothelioma. This means surgery can potentially remove the entire visible tumor. Surgery is the standard treatment for most patients with this mesothelioma type.
For pleural epithelioid mesothelioma, an extrapleural pneumonectomy, or EPP, is a possible treatment. EPP is a surgical procedure that removes the lung along with the pleura where the cancer originated. Patients must be in generally good health for this complicated and risky surgery.
A less aggressive surgical strategy is called debulking. Debulking is a procedure where a surgeon removes as much of the tumor as possible. Surgery may also be done to remove the pleura on one side of the chest or part of a lung. These are usually combined with chemotherapy and radiation for best results.
Other Treatments for Epithelioid Mesothelioma
Targeted therapy is a cancer treatment that uses drugs which targets specific oncogenic genes or proteins in the tumor. Dasatinib, for example, a multitargeted Src kinase/PDGFR inhibitor, was shown to have an antitumor activity against malignant epithelial mesothelioma patients in phase II clinical trials.
Immunotherapy is used to treat cancer patients using the body’s immune system. Cancer immunotherapies use antibodies that bind to and inhibit functions of proteins, called checkpoints. Most common targets for immunotherapy are PD-1 or PDL1. PDL1, for example, is a protein that helps keep immune cells from attacking normal cells in the body; however, cancer cells express this protein in high amounts to “trick” the immune system into leaving them alone. The therapy blocks it so the immune system recognizes the cancer cells and attacks them.
There are multiple phase II clinical trials investigating the efficiency of immunotherapy drug Nivolumab alone or in combination with another drug called ipilimumab for malignant epithelial mesothelioma patients.The FDA recently approved the combination for pleural mesothelioma, but it is still in the trial phase for peritoneal mesothelioma.
What Is the Outlook for Epithelial Mesothelioma?
Because epithelial cells stick to one another, they metastasize less readily than sarcomatoid cells. Epithelial mesothelioma has the best prognosis compared to other cell types for this reason. Epithelial cells will eventually metastasize, but they will do so more slowly.
In one study, patients with sarcomatoid mesothelioma had a median survival time of just thirteen months. For the patients with epithelial mesothelioma, the median survival time was fifty-five months.
Other factors affecting prognosis include age, gender, general health, nutrition, and cancer stage. The earlier the stage, the better the prognosis will be; therefore, getting an early diagnosis is essential. If you have been exposed to asbestos during your career, you should receive regular mesothelioma screenings.
If you are diagnosed with mesothelioma, there are legal avenues to seek compensation. This includes lawsuits, settlements, and asbestos trust funds. A qualified lawyer can help you navigate your resources and help you make a case.
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