Mesothelioma: A Review

Mesothelioma is an insidious disease with long latency after asbestos exposure. New cases are continually diagnosed, although levels are declining with recognition of the asbestos risk and efforts to remove asbestos from the workplace. Treatment for early stage disease with surgery and radiation is potentially curative, but many patients either are too ill to undergo aggressive surgery or present with advanced disease.

Chemotherapy with cisplatin and pemetrexed is considered standard, although relapse is common. Second-line therapy is disappointing. New targeted therapies may pose promise and are being addressed in various clinical trial settings. Palliative care remains an important component of the management of this devastating illness.

Mesothelioma has been described as an insidious neoplasm because of its long latency period—up to 40 years in some series—after exposure to asbestos. It arises in the mesothelial surfaces of tissues in the pleura but can also occur in the peritoneum and the tunica vaginalis.1 Peak incidence occurs in the 5th and 6th decades of life. Surveillance Epidemiology and End Results (SEER) registry data report approximately 3,300 new cases annually, compared to nearly 200,000 cases of lung cancer.2 With recognition of asbestos exposure risks in the workplace and better controls, the incidence of mesothelioma in the United States (US) has declined over the past decade; however, there are still areas of endemic clustering, usually around regions of high asbestos-related industry such as shipping. In some parts of the world, the incidence is still on the rise.

In Louisiana, for the period between 2000 and 2008, SEER registry data recorded 182 cases in the greater New Orleans area compared to 309 cases statewide.

The impact of Hurricane Katrina in 2005 was taken into account. Louisiana Tumor Registry data for 2009 documented 12 cases in the New Orleans area—including the parishes of Jefferson, Orleans, and St. Bernard—and 57 cases statewide. Males were three times more likely to be diagnosed than females, and more than half of the patients presented with stage III or stage IV disease.

Researchers have examined the association between asbestos and respiratory ailments for decades. A 1980 comprehensive review of asbestos-associated disease estimated that 8% of asbestos workers died of respiratory failure from the chronic morbidity of asbestos-induced pulmonary fibrosis.4 The risk of developing mesothelioma was described as 10% over the lifetime of an asbestos worker, with up to 70% of all mesothelioma cases involving documented asbestos exposure. Concomitant smoking enhances the risk of malignancy in an asbestos worker, with a 60-fold increased risk of developing non–small cell lung cancer. The chance of dying of a malignancy (mesothelioma or lung cancer) versus a nonmalignant cause is 50% in an individual exposed to asbestos compared to 18% in an individual not exposed. Asbestos workers are at highest risk, but family members can also be at risk via exposure to fibers brought home on the clothing of the primary individual.

The majority of asbestos fibers are either amphibole (sharp, rod-like) or serpentine. The serpentine fibers make up 90% of the type seen in the US and are considered less carcinogenic than the amphibole type. These fibers are typically found in brake linings, ship building, cement, and ceiling and pool tiles. The Occupational Safety and Health Administration (OSHA) set acceptable levels of exposure at 0.2 fibers/mL3 for fibers 5 microns or greater and up to 5 fibers/mL3 for smaller fibers.

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