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INTRODUCTION

The pleura is a membranous structure covering the entire surface of the lung and lining the inside of the chest cavity. It is composed of a thin mesothelial layer with underlying fibroblasts and varying amounts of collagenous fibrous tissue with interdigitating capillaries and venules. The most common tumors of the pleura are metastatic neoplasms, predominantly of lung, breast, or colonic origin. Tumors arising primarily from the pleura are rare but still constitute a variety of benign and malignant lesions from several different cells of origin, some of which have yet to be identified.

MALIGNANT MESOTHELIOMA

The most common primary malignant tumor of the pleura is malignant mesothelioma, an insidious neoplasm with a generally dismal prognosis arising from the mesothelial surfaces of the pleural and peritoneal cavities, as well as from the tunica vaginalis and pericardium. Eighty percent of all cases of mesothelioma are pleural in origin.

Epidemiology

The incidence of mesothelioma in the United States is estimated to be 3300 cases per year.1 The incidence within the United States peaked in the year 2000 and is now declining, secondary to control of asbestos exposure.2 However, incidence is increasing in other parts of the world, such as Europe, Japan, and Australia. Deaths from mesothelioma in Great Britain continued to increase and peaked at an annual average of 2540 deaths per year between 2012 and 2018 before decreasing to 2369 in 2019. However, this trend was largely driven by a peak and decrease in deaths among males, and it is unclear when female deaths will peak (https://www.hse.gov.uk/statistics/causdis/mesothelioma/mesothelioma.pdf).3 Subsequent mesothelioma rates were expected to drop in England and other developed countries because of legislation aimed at reducing asbestos exposure in the workplace and the general environment. In contrast, mesothelioma incidence rates are predicted to escalate for much longer times in developing countries because of poor regulation of asbestos mining and widespread industrial and household utilization of asbestos.3–5

Etiology

Inhalational exposure to asbestos has been clearly established as the predominant cause of malignant mesothelioma in humans. Approximately 70% of cases of pleural mesothelioma are associated with documented asbestos exposure. In ancient Greece, the philosopher Pliny first established the association between asbestos exposure and lung disease by making the observation that slaves working in asbestos mines were less healthy than other slaves. It was not until 1960, with the publication by Wagner et al.6 of a series of 33 mesothelioma cases occurring in a crocidolite mining community in South Africa, that the etiologic connection between asbestos and mesothelioma was established. Wagner’s study was soon followed by several other accounts of mesothelioma afflicting asbestos workers at locations around the world. In addition to asbestos miners and workers, other occupations at especially high risk include plumbers/pipefitters, mechanical engineers, and ship and boat building and repairing.4

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