Mesothelioma is an aggressive type of cancer that affects the cells lining and covering certain organs, including the lungs and heart. This type of cancer is caused by exposure to asbestos, a natural mineral that was widely used in construction before it has been demonstrated toxic during the 20th century. Despite the fact that its use is now limited, exposure is still a reality and there are 2,000 to 3,000 new cases of mesothelioma every year in the US alone. Long-term and continued asbestos exposure is usually the cause for mesothelioma, but short-term or once-term exposures can also trigger the disease.

The National Institutes of Health (NIH) estimate that only between 1940 and 1978, 11 million people were exposed to asbestos, as well as that on average it takes 20 to 50 years for the symptoms to develop. There are different types of mesothelioma, being the most common definition divided by location. In addition, there are also different types of mesothelioma tumors and mesothelioma cell types. All the different types of mesothelioma have as common feature its main cause, which is exposure to asbestos.

Types of Mesothelioma by Site

  • Pleural Mesothelioma

Pleural mesothelioma is the most common type of malignant mesothelioma, accounting for about 75% of all cases. The name relates to the location where it develops, the pleura, which is the tissue lining the lungs. Symptoms vary from patient to patient, but they tend to include shortness of breath, persistent dry cough, persistent chest pain, difficulty swallowing, night sweats or fever, and fatigue. The stages of the disease are determined to define the treatment, but pleural mesothelioma is usually treated with curative surgery when it is diagnosed in early stages or with palliative care at later stages. All of the treatments are meant to improve patients’ quality of life since there is currently no cure for any type of mesothelioma.

  • Peritoneal Mesothelioma

Peritoneal mesothelioma is a type of cancer that develops in the mesothelial lining of the abdomen, known as the peritoneum. It is the second most common type of mesothelioma, accounting for about 20 percent of all cases of the disease. The symptoms can slightly differ from the other types of mesothelioma and include abdominal pain, abdominal swelling, weight loss, nausea or vomiting, constipation or diarrhea, and fatigue. These symptoms are related to the thickening of the peritoneal membrane and the build-up of fluid, while peritoneal mesothelioma is the type of mesothelioma faster in spreading throughout the body. Due to this characteristic, treatment, which is usually done with heated chemotherapy, is particularly difficult.

  • Pericardial Mesothelioma

Pericardial mesothelioma is one of the rarest types of mesothelioma and is named after the initial location of the cancer, on the exterior lining of the heart, known as the pericardium. Only about one percent of all mesothelioma patients develop pericardial mesothelioma, which occurs due to the accumulation of fluid in the spaces between the layers of the pericardium. The symptoms of the disease include irregular heartbeat, chest pain, difficulty breathing, coughing, night sweats or fever, and fatigue. In the case of pericardial mesothelioma, treatment is mostly based on palliative care to help ease the symptoms since the location too close to the heart can make surgical removal of the tumor too dangerous.

  • Testicular Mesothelioma

Testicular mesothelioma is developed in the lining of the testicles, a tissue known as tunica vaginalis. It is the rarest type of mesothelioma, accounting for less than one percent of the cases, which makes it difficult to analyze. Misdiagnosis is very common and there are even patients only diagnosed by undergoing surgery or treatment for another condition. Given the rarity of testicular mesothelioma, a complete list of symptoms has not been established, but it is known that painless testicular lumps and swelling of the scrotum are common indicators. In the case of testicular mesothelioma, surgery to remove part or all of the testicle affected is one of the most common treatment options, which physicians may also recommend adjuvant therapy, including chemotherapy or radiation therapy.

Types of Mesothelioma Tumors

  • Malignant Mesothelioma

Malignant mesothelioma is the name given to mesothelioma that is cancerous, in contrast to non-cancerous mesothelioma. Since the former is more severe and common that the latter, it is usually only known as mesothelioma. However, Malignant mesothelioma is particularly rare compared to all other types of cancer. Malignant mesothelioma occurs when cancerous cells develop in the thin cell lining of the body’s internal organs and structures. Pleural, pericardial, peritoneal and testicular mesotheliomas are all types of malignant mesothelioma. This type of cancer can be difficult to diagnose since the symptoms are usually only noticeable when the disease is in advanced stages. Malignant mesothelioma usually has a poor prognosis, while treatment options include chemotherapy, radiation therapy, and surgical resection.

  • Benign Mesothelioma

Benign or non-malignant mesothelioma is a type of tumor that develops due to exposure to asbestos, but unlike malignant mesothelioma, the latency period is much shorter. Similarly, benign mesothelioma is much easier to treat than malignant mesothelioma, however, it can be an indicator of more severe diseases that could develop later in life. Benign tumors grow and impact nearby organs, causing damage, but they do not invade nearby tissues or spread to other parts of the body. Symptoms of the disease include dry cough, difficulty breathing, shortness of breath, and chest pain, while treatment is usually made through surgical resection and the survival rate is generally high.

Mesothelioma Cell Types

  • Epithelial Mesothelioma

In addition to location and whether the disease is malignant or not, the type of cells also differs among mesotheliomas. Epithelial mesothelioma cells are organized and structured, as well as the most common cell types, accounting for about 50 to 75% of all cases. These types of cells can be seen microscopically as uniformly shaped, with an elongated pattern and visible nuclei. Epithelial mesothelioma cells are the ones that develop on any of the mesothelial linings.

  • Sarcomatoid Mesothelioma

Sarcomatoid mesothelioma cells are less common, verified in only seven to 20% of the cases. They are random and irregular, growing out of supportive structures like muscles or bones. Under the microscope, these cells are elongated and spindle-shaped, without a nucleus. The diagnosis of sarcomatoid mesothelioma cells is more difficult, since they resemble healthy tissue. In addition, sarcomatoid mesothelioma cells are particularly resistant to treatment, resulting in a poor prognosis.

  • Biphasic Mesothelioma

Biphasic mesothelioma means that the cells include a mix of both epithelials and sarcomatoids. It is the second most common cellular type of mesothelioma — the equivalent to 20 to 40% of the cases. Since the two types of cells are present, there is no specific structure, and despite the fact that both mesothelioma types are present, they tend to form in differentiated groups in different areas of the tumor. Treatment can be difficult due to the resistance of sarcomatoid mesothelioma cells, and it usually is based on multi-modal therapy that combines radiation and chemotherapy. Surgery is also an option, but only in early stages. In later stages of the disease, palliative care is more common.

  • Papillary Mesothelioma

Papillary mesothelioma or well-differentiated papillary mesothelioma (WDPM) cells are a rare variation of epithelioma cells. It is usually found in women, particularly the ones in reproductive ages. The papillary mesothelioma cells develop in the lining of the abdomen, known as the peritoneum, but they are benign in the majority of the cases. Among men, it can also develop in the tunica vaginalis, and in very rare cases in the pleura for both genders. This type of mesothelioma tends to be painless, it usually does not spread to other parts of the body, and the prognosis is generally favorable. Given the rarity of the disease, there is no standard course of treatment, but there are reports of successful treatment with either surgery, chemotherapy, or radiation therapy.

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