Malignant mesothelioma can occur in the pleural cavity surrounding the lungs, the peritoneum, which is surrounding the abdomen, and the pericardium, which lines the heart. Each type of malignant mesothelioma can be further broken down into three distinct histological categories, or cell types; epithelioid mesothelioma, sarcomatoid mesothelioma and biphasic mesothelioma.
Epithelioid Mesothelioma
Epithelioid mesothelioma is the most common cell type of mesothelioma cancer, and has a definite structure with visible nuclei. This cell type accounts for approximately 60% of all cases of malignant mesothelioma. Epithelioid mesothelioma develops when malignant cells develop on any mesothelial lining, such as the pleural cavity, the peritoneum, and the pericardium.
Unfortunately, when examined under a microscope by a pathologist, these cells resemble healthy epithelial cells, and are uniform in shape and size. Because these cells also are similar to adenocarcinoma cells, it is a good idea for patients who have been diagnosed with adenocarcinoma to be examined for mesothelioma.
There are many different variants of epithelioid mesothelioma cells including papillary mesothelioma, signet ring, single file, adenoid cystic, glandular, tubulopapillary, histiocytoid, and Gaucher Cell-like to name a few. The various shape, size and formation of these cells are what can help determine the appropriate course of treatment for each patient’s mesothelioma.
Epithelial Mesothelioma and Asbestos
It is believed that approximately 70-80% of all mesothelioma cases are linked to working with asbestos. For the family members of workers, they are at an increased risk of developing respiratory problems and mesothelioma as well from exposure to the dust and particles that remain on the clothing they bring home from the work environment.
In the late 19th century, many manufacturers and builders became very interested in a long, thin fibrous crystal known as asbestos. They began mining it and using it for electrical insulation in hotplate wiring and building insulation. One of six naturally occurring silicate minerals, asbestos is resistant to heat, fire, electrical and chemical damage. Often, manufacturers would mix it with cement or weave it into fabrics and mats.
Unfortunately, during the manufacturing process, the thin fibers could be released into the air and be either ingested or inhaled, causing serious health problems including mesothelioma, pneumonia, and various respiratory infections. This is because the asbestos fibers would become lodged in the lung tissue and would remain there permanently causing chronic inflammation that ultimately resulted in malignancy.
Papillary Mesothelioma
The most uncommon variation of epithelioid mesothelioma is papillary mesothelioma, also known as well-differentiated papillary mesothelioma (WDPM). Papillary mesothelioma is more commonly diagnosed in women who are still in the reproductive stages of life, but can be diagnosed in men as well.
Papillary mesothelioma usually develops in the lining of the abdomen, or peritoneum, and is most often benign. However, it can be found in the tunica vaginalis, the area that surrounds the testicles, as well as the pleural cavity, the area that surrounds the lungs.
Strangely, papillary mesothelioma tumors usually cause no pain, and the prognosis is usually favorable, and in most cases, no connection to asbestos has been found.
As with the mesothelioma itself, the occurrence of papillary mesothelioma is quite rare. For this reason, there is no specific standard of treatment at this time. Oncologists and surgeons have worked together in the past, and have used surgical methods to remove the tumor, as a treatment modality, or using chemotherapy and radiation therapy to try shrinking the tumor.
Surgery is the preferred method of treatment, because it is rare that papillary mesothelioma spreads beyond the mesothelium to other parts of the body. In some cases, recurrence does occur, but is not necessarily an indication that the patient will later develop a malignant form of mesothelioma.
Sarcomatoid Mesothelioma
Sarcomatoid mesothelioma cells are random and irregular cells that are stretched out and spindle-shaped. They are arranged in a random and irregular pattern, rather disorganized. Unlike epithelioid mesothelioma cells, sarcomatoid mesothelioma cells do not have a nucleus.
However, just like epithelioid mesothelioma cells are hard to distinguish from healthy epithelial cells, the desmoplastic type of sarcomatoid mesothelioma is difficult to distinguish from healthy tissue in most cases. This is one of the many reasons it is difficult to make an accurate mesothelioma diagnosis.
Traditional methods of biopsy pose challenges when it comes to sarcomatoid mesothelioma. Because the sarcomatoid cells often appear similar to benign fibrous tissue, the normal ‘needle core’ method often results in false information. In addition, histological methods of diagnosis make it difficult to tell the difference between sarcomatoid mesothelioma and other types of unrelated sarcomatoid cancers.
When it comes to treatment options, sarcomatoid mesothelioma can be particularly challenging, because it is resistant to treatment with a less than optimal prognosis. The average rate of survival for sarcomatoid mesothelioma is approximately seven months.
Biphasic Mesothelioma
The second most common cellular form of malignant mesothelioma is biphasic mesothelioma, which is a mixture of both epithelioid and sarcomatoid cells. Biphasic mesothelioma accounts for approximately 20-40% of all cases of malignant mesothelioma. Even though both epithelioid and sarcomatoid cell types are present in a biphasic tumor, they tend to form in segregated groups, and are usually not found in the same area of the tumor.
Treatment Options
Regardless of the cell type of the mesothelioma, the three main options are still surgery, whether it’s for palliative care or for curative measures, chemotherapy, or radiation therapy.
Palliative care is when a tumor has metastasized or spread beyond the mesothelium and is difficult to remove completely. In addition, if a patient is too ill to undergo the necessary extensive operations to remove tumors, doctors will choose palliative care measures instead, such as the removal of excess fluid.
Curative surgeries are for when a patient is in otherwise good overall health and tumors are considered to be localized and thought to be able to be completely removed. In some cases however, the microscopic spread of cancer cells is still possible, and often times undetectable on everyday screenings.
Chemotherapy, or treatment with chemicals is another type of treatment you and your doctor may choose in order to shrink or slow the growth of your tumor cells. Chemotherapy done before surgery is called neoadjuvant chemotherapy, and chemotherapy done after surgery is called adjuvant chemotherapy.There are many different types of chemotherapy, but three of the top choices used specifically to treat mesothelioma are pemetrexed IV sold under the brand name Altima, cisplatin and carboplatin.
Radiation therapy is another course of action you and your doctor may choose as a treatment option for your mesothelioma. Radiation therapy is the method of focusing high-energy beams such as X-rays to specific parts of your body to shrink cancer cells. There are two different types of radiation therapy – external beam radiation and brachytherapy.
