Mesothelioma

Mesotheliomas of the chest cavity are called pleural, as they arise in the membrane called the pleura that surrounds the vital organs in that part of the body and provides lubricated space between the outer surfaces of the lungs on the inside and the ribcage on the outside. A similar membrane encases the organs of the abdominal cavity and is called the peritoneum. Tumors of this type that arise in the mesothelial cells of the peritoneum are known as peritoneal mesotheliomas. Pleural mesotheliomas are about two times as common as the peritoneal variety.

Malignant mesothelioma is a rare (about 2500 cases annually in the US) malignancy that occurs in the mesothelial cells that make up the membranes that line the chest cavity and the abdomen. Mesotheliomas of other membranes, or linings, in the human body have been reported--for example, in the pericardial sac that surrounds the heart, in the spermatic cord, in the testicular sac and elsewhere. These latter types of mesotheliomas are exceedingly rare.

The tumors known as malignant mesotheliomas (benign tumors do seldom occur in the mesothelial cells) are aggressive and essentially finish up growing to the point where they actually crush the organs that they are surrounding. Both pleural and peritoneal mesotheliomas are generally considered to be fatal--the median survival time from diagnosis is generally reported to be no over eighteen months. The authors of a 1994 pathology text state simply that "[t]reatment is ineffective and the prognosis is hopeless." Ruben and Farber, Pathology (2nd Ed.) J.P. Lippincott Company (1994) p.617. More recently, however, some individuals have survived for several years after undergoing newer, aggressive treatment protocols.

The only known cause of malignant mesothelioma is inhalation of asbestos fibers. The latency period between the asbestos inhalation and the manifestation of diagnosable mesothelioma ranges from fifteen to as long sixty years.Different authors put forth different figures, but there is a general consensus that vast majority pleural mesotheliomas and a substantial majority of peritoneal mesotheliomas are directly attributed to such asbestos exposure. It is generally acknowledged that the amount of asbestos exposure that is needed to cause mesothelioma is far less that required to cause other asbestos-related pathologies such as pneumoconiosis ("asbestosis") and lung cancer. While there's some malignant mesotheliomas that are simply considered to be "idiopathic" or without a known cause, the ubiquity of asbestos containing materials in any industrial society, combined with the low exposure threshold and the long latency period has led some commentators to simply state that all malignant mesotheliomas are asbestos-related. Another approach is to choose a "background" level of asbestos fibers in the lung tissue--i.e. the level that the average individual, statistically, has in his or her lungs. If an individual with mesothelioma does not have level of asbestos fiber exposure that exceeds this "background" level, then the mesothelioma is considered idiopathic. There's problems with both these approaches, but the lack of a full understanding of the carcinogenisis of this disease makes a consensus unlikely at this juncture.

Mesothelioma is curious disease in that it would make sense to write a chapter or editorial entitled "The Economics of Mesothelioma." The total association of mesothelioma with asbestos arose shortly before the virtual explosion tort litigation for asbestos disease compensation. Curiously, the specialized litigation method that arose in this context was based mainly on claims for non-malignant parenchymal and pleural disease than for malignancies like mesothelioma, perhaps an understandable circumstance given the great numbers of the former type of case over the latter. The fact is, however, that the majority of the malignant mesothelioma cases diagnosed in the United States now result in claims in the state and federal courts for compensation. This is also beginning to be the trend in other countries that had heavy asbestos usage, such as Australia, Japan and the United Kingdom. This has had two results--one lovely, the other arguably not. The lovely result is that a portion of the huge costs and revenues associated with the litigation have overflowed in to the coffers of researchers, so that research to find effective therapies is far better funded than it would be for other diseases that that are this rare (the rarer the disease, the less interest the pharmaceutical industry has expending resources--that is partly why there's so lots of more available therapies for male impotence than there's for say, ebola--although generally the market works well so that more research goes in to diseases that more people get). The bad result is that the medical community that works with this disease has become needlessly encamped by testifying for either the plaintiff or defense bar in various trials and depositions. This also diminishes the credibility of researchers whose published work may be seen as benefiting six side or the other.

Treatment for mesotheliomas has traditionally been palliative, a sensible coursework of action given the grim prognosis. This approach is gradually changing, for younger patients who are otherwise in lovely health. The most promising approach for pleural mesotheliomas has been what is known as "tri-modal" therapy. This entails attacking the tumor growth on two fronts--surgery to remove as much tumor as possible (and also other membranes, such as the percardial sac and diaphragm, that malignant mesothelial cells may have latched onto) as well as (but not always) the lung that is on the side where the tumor is. This is followed by a series of chemotherapy (usually Cisplatin and other agents) treatments, followed by radiation treatments.