Metastatic Disease to the Lung

After the liver, the lung is the second most common site for metastatic disease (Treasure et al., Thorax 69:946-9, 2014). Consequently, 25-55% of patients with malignancy will develop lung metastases at some point during the course of their disease (Crow et al., Cancer 47:2595-602, 1981; Johnson and Lindskog, JAMA 202:94-8, 1967; Abrams et al., Cancer 3:74-85, 1950). The rich capillary network of the lung and its central location in the circulatory system predispose the lung to the arrest and implantation of circulating tumor cells in the terminal pulmonary vasculature with subsequent spread via direct extension or lymphatic spread into adjacent structures. The diagnosis of pulmonary metastatic disease is usually not a major challenge, especially when supported by an appropriate clinical history with known malignancy elsewhere and radiologic evidence of multiple lung nodules. However, distinction of a solitary pulmonary metastasis from a primary bronchogenic carcinoma, especially after a prolonged disease-free interval may be more difficult and usually requires a multidisciplinary approach, including tissue biopsy, for definitive diagnosis. In this chapter, the pathogenesis, patterns of spread, most common metastatic tumor types, and mechanisms of pulmonary metastasis will be discussed.