Rare Cell Types of Mesothelioma

Mesothelioma is a rare type of cancer that can manifest into many different forms. There are three main cell types, or histological types, of mesothelioma, including epithelioid, sarcomatoid and biphasic. Of these three types, there are an array of subtypes, all of which are extremely rare. If a patient is suspected to have mesothelioma, it’s important for physicians to identify the cell type to determine an accurate prognosis and the most effective treatment plan for the individual patient.

How Is Mesothelioma Diagnosed?

Early diagnosis is important to determine viable, effective mesothelioma treatment options for the patient. However, early detection of mesothelioma cancer can be difficult as symptoms can take decades to manifest after exposure to asbestos, the only known cause of the disease. Asbestos exposure and other potential risk factors could signal physicians to the possibility of mesothelioma. When symptoms do emerge, they should be addressed and brought to a physician’s attention immediately.

When symptoms are brought to a medical professional’s attention, they will then likely conduct imaging tests to identify potential tumors, their size and location. If cancer is suspected, the imaging scans can help direct a biopsy of the tumor, which will determine if the cells are benign or malignant, as well as determine cell type. Two studies that doctors will rely on to properly diagnose mesothelioma include histology and cytology.

Differentiating Types of Mesothelioma

Mesothelioma can be difficult to accurately diagnose for a variety of reasons. Symptoms and masses of malignant pleural mesothelioma, pericardial mesothelioma and peritoneal mesothelioma often mimic other conditions and cancers, including lung cancer, testicular cancer, lymphoma and other, more common diagnoses. Tumors may also contain a variety of cancer cells that complicate an accurate diagnosis and can require more than one biopsy. Rare cell types can be particularly difficult to pinpoint as they emerge in so few cases, so specialists have little data to rely on. Most subtypes fall under the category of sarcomatoid mesothelioma or epithelioid mesothelioma, and each has its own set of characteristics, varying based on location, cell structure, symptoms and rates of recurrence.

Malignant vs. Benign Mesothelioma

Upon collecting a tissue sample through a biopsy, specialists will determine whether a mass is malignant or benign. Benign tumors are non-cancerous and are therefore much easier to treat with a significantly better prognosis. Some cases of mesothelioma are benign and are often treated with curative surgery. For those that are malignant, a treatment plan will be determined on a case-by-case basis, dependent on type, stage at diagnosis and patient characteristics, such as age and health.

For patients diagnosed with a benign form of mesothelioma, it’s pertinent that they set up frequent follow-ups with a mesothelioma specialist for long-term monitoring of potential recurrence. Some subtypes are more likely to recur than others, and recurrence can result in malignancy. With early detection, malignant mesothelioma can be addressed more aggressively with a longer life expectancy for the mesothelioma victim.

Epithelioid Mesothelioma Subtypes

When taking epithelioid, sarcomatoid and biphasic mesothelioma cell types into account, epithelial mesothelioma is the most common, composing about 70% of all malignant mesothelioma cases. Epithelioid mesothelioma is most commonly seen in the pleura (lung linings), but can also be found in the abdomen, genitals and other reproductive organs. In general, epithelial cell types are easier to treat than sarcomatoid, as they are less aggressive and more responsive to treatment. However, rare subtypes may differ.

Adenomatoid Mesothelioma

Adenomatoid mesothelioma is referred to in literature as both glandular mesothelioma and microglandular mesothelioma, found in both men and women.

Most cases of adenomatoid mesothelioma are benign, but there is a potential for malignancy. For benign cases, the typical mode of treatment is surgery, with a goal to completely remove the tumor. For malignant diagnoses, mesothelioma patients will likely undergo multimodal treatment (combination of surgery, chemotherapy and/or radiation). Local or distant recurrence is possible, so long-term monitoring is important despite its benign nature.

Cystic Mesothelioma

Cystic mesothelioma, commonly referred to throughout case studies as multicystic mesothelioma, has a generally better prognosis than the other subtypes. It is most commonly seen in women of reproductive ages and is often seen as benign cystic mesothelioma.

Surgery has proven to be highly effective for this type of mesothelioma. However, cystic mesothelioma has a high rate of recurrence, so follow-up is crucial to ensure the disease doesn’t return in a malignant form.

Deciduoid Mesothelioma

This type of mesothelioma is extremely rare and unique with a limited number of recorded cases. Many cases diagnosed in women have no history of asbestos exposure, leaving many to believe that hormonal imbalances are a potential cause, though there have been some cases linked to asbestos. The prognosis for malignant mesothelioma is generally poor with an average life expectancy of around 1 year. However, deciduoid is even worse, with an average survival of 5 or 6 months.

With the aggressive metastasis of deciduoid mesothelioma and lack of cases, there is little known about the best mode of treatment. Typically, surgery is attempted to remove as much of the cancer as possible, if that’s a viable option for the patient. Otherwise, palliative care is the most common treatment plan, aiming to keep patients as comfortable and symptom-free as possible.

Papillary Mesothelioma

Commonly known as well-differentiated papillary mesothelioma (WDPM), papillary mesothelioma is a disease found often in women of reproductive ages. However, men have also been diagnosed. Prognosis is typically favorable for patients diagnosed with this type.

Based on all reported cases of papillary mesothelioma, most are benign, making prognosis generally favorable with surgical resection as a popular treatment option.

Small Cell Mesothelioma

Like many other subtypes, small cell mesothelioma has presented in very few cases and is often misdiagnosed for more common cancers and conditions, such as small cell carcinoma and small cell lung cancer. Some cases have been biphasic with tumors containing a mixture of epithelial and sarcomatoid cells, but most cases have been classified as epithelioid small cell mesothelioma.

Based on its rarity, mesothelioma specialists have yet to define a clear treatment plan for this subtype. Surgical resection has been used on some patients, involving surgeries such as a extrapleural pneumonectomy to remove as much of the cancer as possible. When diagnosed as epithelial, treatment can involve a combination of surgery, chemotherapy and radiation, but again, will vary based on the patient’s individual case.

Sarcomatoid Mesothelioma Subtypes

Malignant sarcomatoid mesothelioma is the rarest of the three main cell types and the hardest to treat due to its aggressive nature. Treatment is extremely complicated for sarcomatoid mesothelioma and physicians typically suggest palliative care, as conventional treatments may not be viable for the patient.

Desmoplastic Mesothelioma

Desmoplastic mesothelioma is mostly classified as a sarcomatoid subtype, though there have been rare cases of epithelial and biphasic variations. Survival rate is bleak, with one study citing survival of just around 6 months after patients started to experience symptoms.

In terms of treatment of desmoplastic mesothelioma, chemotherapy and radiation may be used to shrink the tumor, and surgery is usually not a viable option. Palliative procedures or surgery may be done through a pleurodesis or paracentesis to drain fluid buildup and alleviate symptoms, such as pain and shortness of breath.

Heterologous Mesothelioma

Heterologous tumors are exceedingly rare with little known about them, especially in terms of progression, prognosis and the best mode of treatment. Most heterologous tumors are of the sarcomatoid type, though biphasic and epithelioid cell types have been seen. The two most common types of heterologous mesothelioma tumors that have emerged are tumors with osteosarcomatous elements and chondrosarcomatous elements, differentiated by what type of cells are present in the tumor.

Heterologous tumors contain cells from other bodily tissues, those separate from the point of origin. Osteosarcomatous tumors contain bone cells, while chondrosarcomatous tumors contain cartilage cells. The mixture of cell types can further complicate a mesothelioma diagnosis and require multiple biopsies for specialists to gain an accurate portrayal of the cancerous mass.

Treatment can vary widely for heterologous mesothelioma, but may include a multimodal treatment and palliative care for the array of symptoms that this type may present.

Lymphohistiocytoid Mesothelioma

Some biphasic cases of lymphohistiocytoid mesothelioma have been seen, but recorded cases are primarily of the sarcomatoid cell type. Commonly diagnosed as non-Hodgkin lymphoma, lymphoepithelial carcinoma and sarcomatoid carcinoma, lymphohistiocytoid mesothelioma is hard to recognize and one of the rarest subtypes.

When looking at treatment options for this subtype of mesothelioma, there is a minuscule amount of clinical studies to go off of, as lymphohistiocytic mesothelioma makes up only 1% of these cancer cases. Surgical resection has been done to improve survival, and chemotherapy and radiation therapy are also likely options.

The Challenges of Rare Mesothelioma Cell Types

Researchers and physicians often rely heavily on previous cases and clinical studies to understand the best way to address a disease. For rare types of mesothelioma, case numbers are so small that there isn’t a lot of previous history to reference when looking for the most effective treatment. It’s also difficult to provide an accurate prognosis for the patient to confidently understand how the disease is expected to progress.

Misdiagnosis is a concern for any disease or health condition. However, misdiagnosis becomes particularly challenging with mesothelioma, as this cancer can be extremely aggressive and must be caught in the early stages. Everyone should be cognizant of their health, and if mesothelioma symptoms are suspected, medical attention should be sought right away. There are mesothelioma doctors that can help identify the presence and type of mesothelioma, as well as the most effective treatment plan.