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Malignant metastasis to the lung is common because of the lung’s rich blood supply, and may present as a solitary enlarging nodule, as multiple nodules, or with diffuse lymphatic involvement.

About 10% of all round pulmonary lesions are metastases, but some 70% of round lesions in patients with a known malignancy. Colorectal cancer is reported to be the commonest tumour of origin. Diagnosis can usually be secured by percutaneous CT-guided biopsy. In rare cases, surgical excision may prolong survival or result in cure, depending on the state of the primary tumour and the likelihood of other occult metastases.

Multiple metastases range enormously in size and number, from ‘cannon balls’—which are the commonest appearance—to multiple lesions of varying size, and then to miliary shadowing, which may be accompanied by hilar lymphadenopathy or pleural effusion. Breast, colon, renal, melanoma, and lung primaries are probably the commonest underlying tumours, but other tumours amenable to chemotherapy occur, such as testicular cancer, choriocarcinoma, and also sarcomas. Diagnosis may be achieved by cytology or histology on various samples from the pleura or lung and can occasionally be made from cytology of expectorated or induced sputum. Tumours that are suitable for chemotherapy (e.g. choriocarcinoma) or endocrine manipulation (e.g. breast) need to be recognized. Solitary or multiple Kaposi’s sarcoma is a feature of AIDS and can involve the bronchi and pleura as well as lung tissue.

Resection remains the treatment of choice and good prognostic factors include the time from treatment of the primary tumour to the development of lung metastases, the fewer the number, the absence of extrapulmonary metastases, and the longer the tumour doubling time. The most favourable group are younger patients with a good performance status, with sarcomas who present with few lesions a year or more after successful treatment of the primary disease. Survival following surgical excision is summarized in Table 18.19.2.1.