Mesothelioma - Basics
Anatomical location of pleura
Definition and Epidemiology
Definition : Mesothelioma is malignant tumor or cancer which arises from the membrane like lining of the internal organs. These serosal membranes are called pleura (See figure) when they cover the lungs, pericardium - covering of the heart and peritoneum - covering of the internal organs located in the abdomen. Most commonly the tumor arises from the pleural surface, which is the membrane like structure enclosing the lungs and internal surface of the chest cavity. In normal state the thickness of these membranes ranges from 0.2-0.5 mm and these membranes are very soft and elastic but in mesothelioma these membranes thicken to great extent ( in the range of many centimeters) and become very rigid and firm. This forms a plaque like firm casing around the lungs, also called as "pleural plaques", which eventually may develop into condition called mesothelioma depending on many biological factors.
Mesothelioma can be benign (one which does not progress or kills the patient), of low malignant potential (one which recurs even after extensive surgery) and malignant (one which have worse outcome in terms of progression of disease and resistance to various forms of treatment).
Pathology of Mesothelioma
Introduction: Malignant mesothelioma is most commonly diagnosed in older patients. Most commonly the tumor presents with chest pain and fluid accumulation in the pleural space (pleural effusion). The initial involvement is usually limited to the one half of pleural cavity but subsequently as malignant tumor progresses the entire pleural cavity gets thickened and studded with malignant nodules. The relationship between asbestosis and mesothelioma was first identified in South Africa. Further research have well documented and proven this relationship of Asbestos as the causative factor. The prevalence on average in patients with "heavy exposure" to asbestos is in the range of 2-5%. Some studies have shown higher percentage of up-to 10%. It takes many years from exposure to the development of mesothelioma (in the range of almost 20 years). It is also important to note that up-to one third of mesothelioma cases might not be associated with exposure to asbestos. Risk of development of mesothelioma following asbestos exposure is also related to the genetic make-up of the individual and exposure to additional carcinogenic agents such as SV-40 (Simian Virus 40).
Asbestos: Asbestos is the chemical form of hydrated silicates and is subdivided into two major categories. 1) The serpentine form and 2) The amphibole form. The sub-forms in both the groups of commercial importance are Chrysolite (Serpentine form) and Amosite and Crocidolite (Amphibole form). These mineral forms were extensively used in construction, predominantly for heat insulation and fire proofing. However, the use of asbestos had been banned since 1972. The above mentioned forms exist as microscopic particles and get to the lungs and pleura via breathing or inhalation. Once the asbestos fiber reaches the pleura and lung, it results in various disease process, depending on the type of form involved, size and concentration of fibers in the inhaled air and duration of exposure. The two main manifestations of asbestos exposure in lung are 1) Pleural plaques and 2) Mesothelioma.