Epithelial Mesothelioma

An asbestos-related cancer, epithelial mesothelioma originates from the lining cells (mesothelium) present in the pleural and peritoneal cavities, and also in the pericardium and the tunica vaginalis. A precise rate of prevalence is not known, but estimates indicate that occurrence of mesotheliomas is less than 1% of all known forms of cancer. The incidence rate of mesotheliomas is on the rise and it is anticipated that it will peak in the coming 10-20 years time frame. Epithelial tissuecovers and lines body cavities.

The most commonly occurring form of epithelial mesothelioma is pleural malignant mesothelioma. The presenting features are usually chest pain and dyspnea. Breathlessness (without chest pain) resulting from pleural effusion also occurs in approximately 30% of patients. Less common presentations include weight loss, a chest wall mass, abdominal pain, sweating, and ascites (resulting from peritoneal involvement).

Epithelial mesothelioma occurs most often in adults; usually surfacing between the ages of 50 and 70, with 70-80% instances in men. In more then 90% of cases, the occurrence of mesothelioma is directly related to a history of occupational asbestos exposure. Available evidence also shows that mesothelioma can occur due to both para-occupational exposure and “environmental” (non-occupational) exposure. Individuals diagnosed in the 20-40 age groups have usually been exposed to asbestos as children. There have also been instances of idiopathic and spontaneous mesothelioma that occur without any exposure to asbestos. These have a spontaneous rate of about one per million in humans.

To make a diagnosis, doctors use a combination of a history of asbestos exposure and radiology and pathology examination. It is a challenge to differentiate between malignant and benign pleural disease. Some of the CT findings that help indicate presence of pleural disease include – 1) nodular pleural thickening, 2) a circumferential pleural rind, 3) mediastinal pleural involvement, and 4) pleural thickening of less than 1 cm. An immunohistochemical screening can also be useful for diagnosis.

Typical symptoms included chest pain, dyspnea, or both, and in one particular series, one-third of patients had experienced breathlessness without chest pain, due to pleural effusions. Although, the chest pain is usually dull and boring in nature when symptoms manifest, patients can experience a pleuritic-type pain due to pleural effusions. The mediastinal structures are usually involved, but superior vena caval obstruction and hoarseness of the voice do not lead to any major symptoms. Occurrence of dysphagia (difficulty swallowing) is also possible, albeit this is discovered late. Unlike bronchogenic carcinomas, it is rare that patients experience lymphadenopathy, haemoptysis, and metastatic symptoms. Weight loss, sweating, and a chest wall mass are less common symptoms. Non-specific symptoms that usually indicate the possibility of epithelial mesothelioma include nausea, loss of appetite, constipation, diarrhea, vomiting and occasionally ascites. Symptoms such as small bowel obstruction usually manifest in later stages.

Physical examination has limited use since it can only detect pleural thickening due to tumor infestation and signs of pleural effusion. Finger clubbing has a higher incidence in comparison to other benign asbestos related pleural diseases and is a possibility in up to 30% of cases. The tumor develops mainly on the parietal pleura, after which it starts spreading via the fissures, to eventually encase the lung surfaces. Pericardium infiltration can lead to cardiac tamponade symptoms and epithelial mesothelioma can spread along surgical incisions and needle tracks. Blood tests can be used to diagnose an elevated erythrocyte sedimentation rate (ESR). In certain isolated cases, mesothelioma has also been associated with symptoms such as autoimmune haemolytic anemia.

Treatment is often conducted by a multidisciplinary medical team to facilitate efficient and appropriate management, based on an effective combination of radiotherapy, chemotherapy, surgery, and symptom palliation supported by end of life care. Other factors that need to be considered include compensation issues. Life expectancy is poor; the median survival being one year after diagnosis.

Deciduoid Mesothelioma

This is a sub-category of epithelial mesothelioma, in which the cells are deciduas-like. The malignant cells are large and have cytoplasm that picks up the staining dye and stands out when viewed under the microscopic.

This type is about 2% to 5% of all mesothelioma cases and more than half of deciduoid mesothelioma cases are in the abdomen. Based on a limited number of cases, it appears this type of mesothelioma may be more common in women. Prognosis is the same as for other types of mesothelioma.

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