Pleural Mesothelioma

The incidence of pleural mesothelioma will probably increase in the coming years. A complete occupational history should include an inquiry about asbestos exposure, especially in patients with chest pain or dyspnea. The latency period between exposure and mesothelioma is as long as 50 years. In some patients, early diagnosis leads to a chance of cure.

In most cases, however, there is no cure. Accurate diagnosis and a frank discussion of prognosis will allow patients to prepare for death. Pleural mesothelioma is a mesenchymal tumor that occurs primarily in the pleura (80 percent of cases) or the peritoneum (20 percent of cases). (1) First described in 1870, the association between mesothelioma and asbestos was not convincingly documented until 1960, when high tumor rates were found in South African asbestos miners. (2) Mesothelioma is a rare tumor, with an incidence rate of one to two cases per 1 million persons per year.

In some asbestos-exposed groups, however, mesothelioma accounts for 10 percent of all deaths. (3) Early diagnosis is crucial for any hope of cure. Even in typical cases where cure is impossible, the diagnosis is important so that patients can prepare for death, both psychologically and practically.

Epidemiology

The term "asbestos" refers to any of a group of naturally occurring fibrous silicates, mainly crocidolite (blue asbestos, mined in South Africa), chrysotile (white asbestos, mined in Canada, the United States and the Soviet Union), amosite (brown asbestos, mined in South Africa) and anthophyllite (mined in Finland).

Exposure to asbestos is the number one risk factor for malignant mesothelioma. Of the types of asbestos, crocidolite is by far the most dangerous, followed by amosite and chrysotile.

There is a latency period of 20 to 50 years between asbestos exposure and the development of mesothelioma. It was estimated that the incidence of mesothelioma would peak in the late 1980s, because of the heavy asbestos use in the shipbuilding industry during World War II.(6) Two considerations make it appear likely that the incidence of mesothelioma will continue to rise into the early twenty-first century.

First, the safe level of asbestos exposure is unknown. Most risk estimates are extrapolated from studies of heavily exposed individuals. The relevance of these data to lightly exposed persons is unclear. Most urban dwellers have some asbestos fibers in their lungs.

Family members of asbestos workers have developed mesothelioma, as have persons living in the vicinity of asbestos plants. Some cases of mesothelioma have been reported in persons who were exposed to asbestos for a period as short as two days.

The uncertainty over safe levels of asbestos exposure is illustrated by recent government actions. In June 1987, the Occupational Safety and Health Administration lowered permissible exposure levels from less than 2 fibers per cubic centimeter of air to less than .01 fibers per cubic centimeter of air. The Environmental Protection Agency is considering a total ban on asbestos. There is, apparently, no proven safe threshold level.

The second reason for the growing incidence of mesothelioma is the fact that asbestos is still widely used in manufacturing and industry in the United States. Its strength and superior qualities of heat, acid and sound resistance make it an attractive industrial material. Asbestos is a component of concrete, asphalt, tile, industrial water filters, brake linings, clutch linings, pipes, paints, steam pipe insulation and electric wire insulation. Crocidolite, the most dangerous asbestos, is the fiber of choice for large-diameter pressure pipes.

Although asbestos is usually bound inertly in these products, fabrication or use of the products often entails drilling or cutting the material, liberating dangerous asbestos dust in the process. Many workers in the construction and manufacturing industries continue to be exposed to asbestos.

Mesothelioma |