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Themaincauses of smoking-related deaths are lung cancer, chronicobstructive pulmonary disease (COPD), and ischemic heartdisease.Smokinghasalsobeenstronglyassociatedwithseveralinterstitiallungdiseases(ILDs),namelypulmonaryLangerhanscell histiocytosis (PLCH), respiratory bronchiolitis (RB), RB-associated ILD (RB-ILD), and desquamative interstitialpneumonia (DIP).This article reviews the major diffuse pulmonary diseasesaffectingsmokers,includingemphysemaandsmoking-relatedILDs. We describe the histologic and radiologic features of thedifferent forms of emphysema (centrilobular, panlobular, andparaseptal). Finally, we then discuss the clinical, histopatho-logic, and radiologic characteristics of smoking-related ILDs,including PLCH, RB, RB-ILD, and DIP. Bronchogenic carci-noma is not covered in this article.

The lungs are a common site for metastatic spread of malignancy. Approximately 20%-54% of patients with extrathoracic malignancy have pulmonary metastases at autopsy. The most common primary neoplasms with pulmonary metastases at autopsy include breast, colon, kidney, uterus, and head and neck. Less common primary malignancies including choriocarcinoma, osteosarcoma, testicular tumors, melanoma, and thyroid carcinoma also metastasize to the lungs. The detection of pulmonary metastases, as with other distant metastases, indicates a poor prognosis and directly affects treatment planning. For example, in a large retrospective study of patients with melanoma, median survival was only 7.3 months after development of pulmonary metastases. Evaluation is primarily performed with chest radiography and computerized tomography (CT), although other modalities such as fluorodeoxyglucose-positron emission tomography (FDG-PET) may also play a role. Pulmonary metastases can have a wide spectrum of appearances on imaging, reflecting the route of spread as well as the local behavior of the neoplastic cells.

Imaging plays an integral role in diagnosing, staging, and following patients with lung cancer. Many lung neoplasms are detected on chest radiographs, but the majority of patients have advanced stage disease at the time of presentation. There is a wide spectrum of radiologic manifestations of lung cancer, and recognition of these findings is essential for patient management. As we continue to understand more about tumor biology, new imaging techniques likely will emerge. Nevertheless, the chest radiograph and CT remain important tools in establishing the diagnosis of lung cancer.