Both lung carcinoma and malignant mesothelioma develop in workers exposed to asbestos. The risk for developing lung carcinoma is increased about 5-fold for asbestos workers; the relative risk for mesothelioma, normally a very rare tumor (2–17 cases per 1 million individuals), is more than 1000 times greater. Concomitant cigarette smoking greatly increases the risk for lung carcinoma but not for mesothelioma. Lung or pleural cancer associated with asbestos exposure carries a particularly poor prognosis.
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Fig. 13.20 Asbestosis.Markedlythickenedvisceralpleuracoversthelateralanddiaphragmaticsurfaceofthelung.Notealsosevereinterstitialfibrosisdiffuselyaffectingthelowerlobeofthelung.
Pneumoconiosesencompassagroupofchronicfibrosingdiseasesofthelungresultingfromexposuretoorganicandinorganicparticulates,mostcommonlymineraldust.
Pulmonaryalveolarmacrophagesplayacentralroleinthepathogenesisoflunginjurybypromotinginflammationandproducingreactiveoxygenspeciesandfibrogeniccytokines.
Coaldust–induceddiseasevariesfromasymptomaticanthracosis,tosimplecoalworker’spneumoconiosis(coalmaculesornodules,andcentrilobularemphysema),toprogressivemassivefibrosis(PMF),manifestedbyincreasingpulmonarydysfunction,pulmonaryhypertension,andcorpulmonale.
Silicosisisthemostcommonpneumoconiosisintheworld,andcrystallinesilica(e.g.,quartz)istheusualculprit.
ThemanifestationsofsilicosisrangefromasymptomaticsilicoticnodulestoPMF;individualswithsilicosisalsohaveanincreasedsusceptibilitytotuberculosis.Therelationshipbetweensilicaexposureandsubsequentlungcanceriscontroversial.
Asbestosexposureislinkedwithsixdiseaseprocesses:(1)parenchymalinterstitialfibrosis(asbestosis);(2)localized fibrousplaquesor,rarely,diffusepleuralfibrosis;(3)pleuraleffusions;(4)lungcancer;(5)malignantpleuralandperitonealmesothelioma;and(6)laryngealcancer.
•Cigarettesmokingincreasestheriskforlungcancerinthesettingofasbestosexposure;moreover,evenfamilymembersofworkersexposedtoasbestosareatincreasedriskforcancer.
Drugs can cause a variety of acute and chronic alterations in respiratory structure and function. For example, bleomycin, an anti-cancer agent, causes pneumonitis and interstitial fibrosis as a result of direct toxicity of the drug and by stimulating the influx of inflammatory cells into the alveoli. Amiodarone, an anti-arrhythmic agent, also is associated with risk for pneumonitis and fibrosis. Radiation pneumonitis is a well-known complication of irradiation of pulmonary and other thoracic tumors. Acute radiation pneumonitis, which typically occurs 1 to 6 months after therapy in as many as 20% of the patients, is manifested by fever, dyspnea out of proportion to the volume of irradiated lung, pleural effusion, and pulmonary infiltrates in the irradiated lung bed. These signs and symptoms may resolve with corticosteroid therapy or progress to chronic radiation pneumonitis, associated with pulmonary fibrosis.