What Are the Major Types of Mesothelioma Cancer Cells?
When mutated, cancerous cells develop in the lining of the abdomen, lungs, or heart — called the mesothelium — they are called malignant mesothelioma cells.
There are three main mesothelioma cell types:
- Epithelioid cells: Most mesothelioma tumors are made up of epithelioid cells. This cell type is the easiest to treat.
- Sarcomatoid cells: These rare cell types are recognized by their large size and spindle shape. It is the hardest cell type to treat.
- Biphasic tumors: Biphasic tumors contain both epithelioid and sarcomatoid cells. Which cell type is dominant will determine how fast the tumors spread and respond to treatment.
Researchers are still trying to understand how and different mesothelioma cell types come about, but they know that these cells follow similar growth and division patterns to other cancer cells.
It is believed that asbestos exposure is the cause of these mutations. When asbestos fibers get into the lung, they begin to slowly move within the body. When they reach lung or peritoneal surface, they irritate healthy cells, eventually causing scar tissue and cancerous cells to form.
Each mesothelioma cell type responds differently to specific treatments, so correctly identifying the cell is key to effective treatment.
For instance, a combination of surgery, chemotherapy, and radiation (called multimodal treatment) is the most common recommendation for epithelioid cells. Surgery and chemotherapy are frequently used for sarcomatoid cells.
Quick Facts About Mesothelioma Cell Types
- Epithelioid cells make up more than half of mesothelioma diagnoses and have a better prognosis (the expected outlook of the disease) than the other cell types, according to the American Cancer Society (ACS).
- The ACS states that sarcomatoid cells account for 10-20% of mesothelioma cases.
- Biphasic tumors make up the remainder of cases (20-30%), according to the ACS.
- The National Cancer Institute (NCI) notes that mesothelioma cell types can be identified under the microscope as tissue (pathology) or as cells within a fluid (cytology).
Mesothelioma Histology and Determining Cell Type
The broad term for studying any type of tissue is called histology. It is used in every type of cancer diagnosis, including mesothelioma.
Histology is very important when diagnosing and treating mesothelioma. By determining which cells are present, doctors can form specialized treatment plans that give patients the best chance of achieving long-term recovery.
How Mesothelioma Cell Type is Determined
Testing for mesothelioma begins with X-rays and CT scans of the chest or abdomen. If those tests show cause for concern, a biopsy will be conducted.
Through a biopsy, a mesothelioma specialist takes a fluid or tissue sample and examines it under a microscope. Through this, the specialist can determine if there are cancerous cells and if so, what type of cells are present.
A biopsy is the only way to confirm a mesothelioma diagnosis.
For this reason, patients should work with a mesothelioma specialist to get their biopsy done. Mesothelioma can resemble other cancer types, leading to a misdiagnosis. General oncologists (cancer doctors) may treat mesothelioma incorrectly.
There are several ways to obtain tissue for biopsy.
Types of biopsies include:
- Thoracoscopy: The most common type of mesothelioma occurs in the lining of the lungs, called the pleura. A thoracoscopy involves using a camera to investigate the lungs and suction a small sample of fluid, which will be investigated for cancer cells.
- Mediastinoscopy: Another procedure involves using general anesthesia to insert an instrument around the windpipe to examine lymph nodes around the windpipe. From there, doctors can take a biopsy from any tumors near the lymph nodes.
- Fine-Needle Aspiration: Similar to the mediastinoscopy, fine-needle aspiration involves inserting a small needle between the ribs during a CT scan session.
- Core Needle Biopsy: This allows a larger needle to take a bigger sample.
Which type of biopsy will be used depends on where the possibly cancerous tumor is located. Once a biopsy has been concluded, doctors can determine which mesothelioma cell types are present.
Epithelioid Mesothelioma Cells
Epithelioid cells are the most common mesothelioma cell type. Epithelioid cells characterized by a single nucleus, uniform appearance, and slow growth.
Doctors use the term “epithelioid” and “epithelial” interchangeably when talking about this type of cancer cell.
There are also several subtypes of epithelial cells depending on where they are found within the body.
These cancer cells typically form in the body’s glands. The most common starting point is the genitals, but they can appear just about anywhere else in the body.
Adding to the confusion, this mesothelioma cell type can be either benign (non-cancerous) or malignant (cancerous). This may make it hard for doctors to determine how serious the cancer is. Further, adenomatoid cells don’t always mean that mesothelioma is present.
For these reasons, it’s important for patients to work with experienced mesothelioma specialists to get an accurate diagnosis.
This is an extremely rare mesothelioma cell type, with only 200 reported cases across the country. Because of this, doctors still do not fully understand this cancer type.
Fortunately, these cells are usually benign. In fact, only one death has been reported from cystic mesothelioma.
One of the most aggressive epithelioid mesothelioma cell types, these cells are shaped like large polygons or ovals and have clearly defined borders.
Papillary mesothelioma, also referred to as well-differentiated papillary mesothelioma (WDPM), is a rare and benign mesothelioma cell type. While there is no clearly proven treatment for papillary mesothelioma, surgery, chemotherapy, or radiation are all possible options.
Small cells are typically found in the peritoneum (abdominal lining), but they have also been found in the pleura (lung lining) and pericardium (heart lining). These cells can even be found in other types of cancer as well.
Researchers are still trying to understand if mesothelioma small cells spread in the same way as they do with other small cell cancers of other organs.
Epithelioid Mesothelioma Prognosis and Treatment
Patients diagnosed with epithelioid mesothelioma have relatively longer survival rates when compared to other cell types. On average, patients with epithelioid mesothelioma live 1-2 years after diagnosis.
However, mesothelioma prognosis is also affected by other factors like the stage of the cancer when it’s found, the patient’s overall health, age, and where the cancer develops in the body. For these reasons, prognoses can vary with each patient.
These factors also affect what type of mesothelioma treatments patients can safely undergo. Patients with epithelioid mesothelioma are typically treated through a combination of surgery, chemotherapy, or radiation.
Types of Epithelioid Mesothelioma Treatment
Epithelioid Mesothelioma Treatment
Surgery is the most frequent solution for epithelioid mesothelioma because epithelioid cells are less aggressive and less likely to return to the tumor site. However, patients who are older or who have underlying health issues may not qualify for surgery.
Epithelioid Mesothelioma Treatment
Chemotherapy uses chemicals to attack and kill tumors. It’s not as effective as surgery, but still a strong option for epithelioid tumors. A combination of pemetrexed and cisplatin or carboplatin is the most common chemotherapy treatment for epithelioid mesothelioma.
Epithelioid Mesothelioma Treatment
Through radiation therapy, electrons are aimed at the tumor to prevent cells from multiplying and to damage them. Radiation alone cannot properly treat mesothelioma, but it can be used in combination with other treatment methods. It’s also used to lessen pain and diminish symptoms.
Specialists generally agree that some combination of surgery, chemotherapy, and radiation is the most effective method of improving prognosis. This is known as multimodal treatment or therapy.
Sarcomatoid Mesothelioma Cells
Sarcomatoid mesothelioma cells are much more aggressive than epithelioid cells. Unlike epithelioid cells, sarcomatoid cells don’t clump into masses. More often they create small nodules that quickly spread throughout the body.
These cells are large and shaped like a spindle. Often, they will combine into fibrous-looking bundles.
The small size of sarcomatoid mesothelioma cells and their resemblance to other types of cancer cells make them difficult to properly diagnose. Fortunately, this is the least common of all mesothelioma cell types, so not as many patients are affected.
Sarcomatoid Cell Subtypes
The following cell subtypes are most commonly found in sarcomatoid cells.
- Desmoplastic: These cells account for about 5-10% of malignant pleural mesothelioma cases. It has a poor prognosis and is one of the more difficult subtypes to diagnose.
- Lymphohistiocytoid: In this subtype, cells from the immune system bundle together in the mesothelium.
- Osteosarcomatous: This extremely rare subtype forms when cancerous bone cells lodge in the mesothelium.
- Chondrosarcomatous: Spindle-shaped cartilage cells growing in the mesothelium cause this subtype to form.
Some of these cell subtypes have been found in cases of epithelioid and biphasic mesothelioma as well.
Sarcomatoid Mesothelioma Prognosis and Treatment
Sarcomatoid mesothelioma frequently forms as small nodules, and it can quickly spread from its origin point to nearby organs. It is also the most difficult mesothelioma cell type to treat, with an average prognosis of six months.
Some treatment options may be available to improve a patient’s prognosis depending on if the cancer is caught before it has spread throughout the body.
Surgery is usually not performed for sarcomatoid mesothelioma because the tumors are rigid and often grow directly into the chest wall. The cancer also frequently returns even after a comprehensive surgery.
Chemotherapy relies on a variety of chemicals to stop and prevent cancer cell growth. Sarcomatoid cells usually receive the same chemical combination as the other types of mesothelioma, which is a combination of pemetrexed and cisplatin or carboplatin.
Radiation cannot effectively rid the body of mesothelioma on its own, but specialists may consider it in combination with other treatments.
Tumors formed by a combination of sarcomatoid and epithelioid cells are called biphasic tumors, or sometimes “mixed mesothelioma.” There are no biphasic cells. It accounts for 20-30% of mesothelioma cases.
Which mesothelioma cell type is dominant will affect how this type of cancer spreads and responds to treatments. A higher percentage of sarcomatoid cells means that biphasic mesothelioma may spread faster through the body. Epithelioid cells do not spread as quickly, but they do grow faster.
Biphasic Mesothelioma Prognosis and Treatment
A common method for identifying biphasic tumors is called immunohistochemistry. This involves coating cell walls with dye to make the proteins within cells more visible. A trained specialist can determine, based on the proteins, which mesothelioma cell type is dominant.
The prognosis for biphasic mesothelioma is one year, although that range from six months to more than five years.
Treatment for biphasic mesothelioma is also impacted by cell type. Sarcomatoid cells do not respond as well to treatment, which can make biphasic mesothelioma harder to treat even if epithelioid cells are present.
Biphasic peritoneal mesothelioma responds well to a combination of cytoreductive surgery with intraoperative heated chemotherapy.
Chemotherapy and Radiation
Neither of these strategies is particularly effective if more sarcomatoid cells are present, but if a biphasic tumor is mainly made up of epithelioid cells then they may be useful.
Seeking Treatment for Your Mesothelioma Cell Type
No matter what mesothelioma cell type you are diagnosed with, there are treatment options available for you. It’s critical that you work with a mesothelioma specialist who can help determine the best mesothelioma treatments available for you.
These specialists can also help you by confirming your cell type before treatment begins. This is extremely crucial because mesothelioma cells closely resemble other cancers, meaning you could be misdiagnosed by a non-specialist and start receiving treatments for the wrong illness.
To learn more about mesothelioma cell types — and how they impact diagnosis and treatment options — download our free mesothelioma guide.