Mesothelioma is a cancer that forms in the mesothelium or the linings that surround various organs. Mesotheliomas are classified by where in the body they form: pleural mesothelioma starts in the lining inside the chest wall and around the lungs, peritoneal mesothelioma starts in the lining of the abdomen, pericardial mesothelioma starts in the lining membrane covering the heart, and testicular mesothelioma starts in the lining of the testicles. The tumors for each of these mesothelioma types are further broken down into mesothelioma cell types. Part of your mesothelioma diagnosis will be your mesothelioma cell type.
By identifying mesothelioma cell types, doctors can make better decisions about your treatment and prognosis. Understanding mesothelioma cell types will help you understand your diagnosis.
Determining Mesothelioma Cell Types
To find out which of the mesothelioma cell types is found in your cancer, your doctor will need to take a biopsy of your tumor. This is followed by examination under a microscope in a medical specialty called histopathology.
What Is Histopathology?
Histology is the study of cells. A pathologist looks at the causes of diseases and their diagnosis by examining the tissue in the laboratory. A histopathologist is a medical specialist who will look at your mesothelioma cells under a microscope and determine which of the mesothelioma cell types is present in your cancer.
Your doctor may use a needle to remove fluid that has built up in between the layers of your mesothelium. A histopathologist may analyze this fluid, but the fluid may not have enough mesothelioma cells to determine the type of cancer or the cell type. To do this analysis, your doctor may need to perform a small surgery called a biopsy.
During a biopsy, a small incision is made near the location of your tumor and a sample of cells is removed. This is called an incisional biopsy. Some patients get an excisional biopsy, in which a large amount of tissue, and perhaps even the whole tumor, is removed before being examined.
After the biopsy procedure, the tissue sample containing your cells is treated with a fixative, a chemical that will preserve the cells until the histopathologist can examine them. Formaldehyde is one commonly used fixative.
Next, your cells will be processed to remove water and add a waxy substance, usually paraffin , to stiffen the tissue so it can be sliced very thinly. This thin slicing is called sectioning. After the sample is sectioned and then stained with a series of special dyes, the pathologist can see the structures in of your cells and determine which of the mesothelioma cell types is present, if any.
Each of the mesothelioma cell types has a distinctive shape and grows in certain formations. Your histopathologist will look at your cells under a microscope and give a detailed report to your doctor. This will provide vital information that your medical team can use to guide your mesothelioma treatment.
Diffuse vs. Localized Mesothelioma
One other distinction in mesothelioma types is whether the cancer is localized or diffuse. Localized mesothelioma forms as one tumor at the site of origin. Diffuse mesothelioma can appear as many small nodes around the point of origin.
Mesothelioma develops many years after you inhale microscopic asbestos fibers. Because the lungs are often the most common point of entry for asbestos, pleural mesothelioma is the most common mesothelioma type.
Asbestos causes cancer in the mesothelium because the mesothelial cells are most vulnerable to the toxic effects of asbestos (though asbestos can also cause lung cancer). It can take many years and as long as several decades after asbestos exposure for mesothelioma cancer to develop.
Diffuse mesothelioma tends to be far more common than localized mesothelioma. Some researchers believe that mesothelioma can never be truly classified as localized into one larger tumor. Mesothelioma is rarely easy to diagnose; some localized tumors in the pleura may be lung cancers that have spread beyond the lungs into the mesothelial lining around the lungs, rather than mesothelioma. A histological examination of the cells in the tumor is the best way to determine whether a tumor is mesothelioma or a different type of cancer.
What Are the Mesothelioma Cell Types?
There are three main mesothelioma cell types: epitheliod, sarcomatoid, and biphasic or mixed. Within each of these types there are subtypes of mesothelioma cells.
Epitheliod Cell Type
The epitheliod mesothelioma cell type is the most common. This is good news, because it is also the most responsive to treatment.
Epitheliod Cell Markers
Epitheliod cells have a distinctive appearance that often makes them easier for histopathologists to spot than some other mesothelioma cell types. The cells are square and it is possible to see the nuclei at the center of the cell under the microscope.
Epitheliod cells reproduce and multiply more quickly than sarcomatoid or biphasic mesothelioma cell types. Despite this, epitheliod tumors are less lethal than the other types. This is because epithelioid cells stick to each other, rather than spreading out. Epitheliod mesothelioma cells are slower to metastasize or spread to other parts of your body. Metastatic cancer is often times more difficult to treat than localized cancer. Because epitheliod cells tend to stay put, it’s easier for your doctor to find and eliminate them through surgery, chemotherapy, radiation, and other mesothelioma treatments.
Epitheliod mesothelioma cell types are further divided into several subtypes. Some are common and some are very rare. Your treatment will probably not be affected by which epitheliod subtype you have, but your diagnosis may be easier or more complex depending on the subtype. Some epitheliod mesothelioma tumors may be composed of more than one of these subtypes.
Some epitheliod mesothelioma cells look very much like the cells for other types of cancer, so your doctor and your histopathologist may have to do some detective work to come up with an accurate diagnosis. It’s important to let everyone on your medical team know if you have a past history of exposure to asbestos. This will alert the histopathologist to look for mesothelioma cell types in your biopsy.
- Small Cell: If at least half of the cells in your tumor are smaller than normal mesothelioma cell types, your mesothelioma may be classified as the small cell subtype. This is considered a subtype of epitheliod mesothelioma but is also found in biphasic mesothelioma tumors. This is a rare variation and may be hard to diagnose because the cells resemble those of other types of cancers and tumors.
- Clear Cell: This uncommon variation of the epitheliod mesothelioma cell type wasn’t even discovered until 1996. Like the small cell type, it’s easy to mistake this form for other types of cancer.
- Tubulopapillary Cell: This is a common epitheliod subtype. The cells are easy to tell apart, but this subtype may still be confused with another form of cancer and misdiagnosed at first.
- Adenomatoid: This uncommon epitheliod subtype has cells that are either flat or cube-shaped. The cells can look like those of noncancerous conditions.
- Deciduoid: This rarely-seen epitheliod subtype has large cells that are either round or shaped like polygons. It can be misdiagnosed as a number of other cancers that have similar-looking cells.
- Solid mesothelial: This subtype is one of the most common epitheliod cell types. It is further divided into two more categories: well-differentiated and poorly-differentiated. The well-differentiated is more common. The cells form into sheets or nests and are round rather than square. The poorly differentiated type doesn’t form into a pattern and the cells are round or roundish. Both of these categories of cells may be misdiagnosed as the cells of other cancers or noncancerous conditions.
- Glandular: As the name suggests, these epitheliod cells form into shapes that look like glands.
Sarcomatoid Cell Type
The sarcomatoid mesothelioma cell type is also called fibrous. This cell type is much less common that epitheliod. Sarcomatoid mesothelioma cells tend to be harder to eradicate with currently available mesothelioma treatment options. They also spread to other areas of your body faster than epitheliod cells. Because of these two factors, mesothelioma patients with the sarcomatoid cell type have a shorter survival time, on average, than epitheliod patients.
Sarcomatoid cell types are almost always found in pleural mesothelioma tumors. Some peritoneal mesothelioma patients may have this cell type, but it’s much rarer.
The cells of this mesothelioma cell type are elongated and look like spindles. They grow in a disorganized manner and, because of this, sarcomatoid cells tend to spread out across the affected mesothelium. Sarcomatoid mesothelioma cells are also more likely to metastasize to other parts of your body. Because metastatic cancer is harder to treat, standard mesothelioma treatments are not as effective for this cell type.
Sarcomatoid Cell Subtypes
Like epitheliod mesothelioma cells, sarcomatoid cells come in several subtypes.
- Desmoplastic Cell: These mesothelioma cells look much like collagen, which is a noncancerous protein that occurs naturally in your skin, bones, and connective tissues. This cell subtype can make it harder to get a mesothelioma diagnosis. Fortunately, it’s very rare.
- Transitional Cell: These sarcomatoid cells have the spindle shape but are more plump.
- Lymphohistiocytoid Cell: These cells also have the sarcomatoid spindle shape but they are larger than other sarcomatoid cells. This is the rarest sarcomatoid subtype.
Biphasic Cell Type
The biphasic or mixed mesothelioma cell type classification indicates that both epitheliod and sarcomatoid cells are present in a mesothelioma tumor. If your mesothelioma is biphasic, the proportions of each of the mesothelioma cell types is an important factor in treatment and survival time. Biphasic mesothelioma patients tend to have better outcomes if they have a larger percentage of epitheliod cells relative to sarcomatoid cells.
If your cancer is biphasic, the two mesothelioma cell types won’t be evenly distributed in your tumor. Each cell type is likely to grow in a different area. Because a biopsy only removes a small sample of cells, it’s easy to miss the fact that a tumor is biphasic. Your mesothelioma specialist may need to take more than one tissue sample or biopsy to get an accurate picture of the makeup of your biphasic tumor.
The Importance of a Biphasic Mesothelioma Diagnosis
It’s important to know whether your tumor is epitheliod, sarcomatoid, or biphasic because this will affect your treatment plan. These subtle differences in mesothelioma cell types can make a big difference in the outcome of your treatment.
If your diagnosis is an epitheliod tumor, then your doctor will proceed on the assumption that your mesothelioma is not likely to metastasize. If your tumor is, in reality, biphasic, the sarcomatoid cells could be spreading to other parts of your body while you receive standard mesothelioma treatments.
It’s important to seek out medical professionals who specialize in working with mesothelioma patients. They will know what to look for during your diagnosis and treatment.
Rare Mesothelioma Cell Subtypes
There are other mesothelioma cell types that are less common than the ones described above. Scientists are studying the histology of mesothelioma all the time and describe new cells as they discover them. By the time you read this, more cell variations may have been found.
Here are some of the mesothelioma cell types that you may hear your doctor discuss. Most of these are subtypes of epithelioid mesothelioma.
- Acinar Cell
- Adenoid cystic
- Large Cell
- Mucin Positive
- Gaucher Cell-Like
- Single File
- Well-Differentiated Papillary
Mesothelioma Cell Types: Diagnosis
Mesothelioma is a rare form of cancer. It can take several steps and multiple tests before you get a mesothelioma diagnosis. On top of that, as noted above, the different mesothelioma cell types and subtypes can resemble other, more common forms of cancer. A pathologist may first consider lymphoma, sarcoma, or adenocarcinoma before looking for mesothelioma.
The sarcomatoid mesothelioma cell type tends to be particularly hard to diagnose because it looks so much like several other cancer cell types. In addition to other cancers, sarcomatoid cells can be incorrectly identified as noncancerous indicators of conditions such as fibrous pleurisy, which is an inflammatory condition affecting the pleura (the lining around the lung).
Misdiagnosis can lead to incorrect treatments and losing precious time. Remember to tell every doctor and pathologist you encounter that you have a history of asbestos exposure. Unless your team is looking for mesothelioma, it is possible to miss it, at least at first.
Mesothelioma Cell Types and Treatment Options
Mesothelioma cell types are vital to determining the best treatment options. When caught in an early stage, both epitheliod and sarcomatoid mesothelioma cell types may be treated with mesothelioma surgery. For pleural mesothelioma, this means either extrapleural pneumonectomy (EPP) or pleurectomy/decortication (P/D). For peritoneal mesothelioma, the most common mesothelioma surgery is debulking or cytoreductive surgery. These procedures remove cancerous tissue and reduce the incidence of metastases.
In most cases, surgery is followed by chemotherapy or other multimodal mesothelioma treatments. Both surgery and chemotherapy in many cases tend to be more effective at extending life for patients with epitheliod mesothelioma cell types than sarcomatoid, so doctors may be more aggressive in treating epitheliod tumors. Palliative care is sometimes the preferred treatment for sarcomatoid mesothelioma.
Patients with biphasic mesothelioma will receive the same treatment regimens as those with epitheliod or sarcomatoid tumors. The aggressiveness of the recommended treatment will depend, in part, on the amount of each cell type in your tumor.
The correct diagnosis of mesothelioma cell type is the first step on the road to optimum treatment and the best result for this usually eventually fatal disease, so it is important to get it right as quickly as possible. Seek help and care at a good mesothelioma specialty treatment center as soon as possible, and work closely with your medical care team for the best chance of a good result.