The lungs are one of the most common sites of involvement for metastatic neoplasms. About 30% of patients with malignant disease will eventually develop pulmonary metastases. For melanomas and sarcomas, the incidence may be as high as 80%.

Therapeutic success depends on early diagnosis, appropriate selection of patients for surgery, complete resection, and a favorable tumor-host relationship.

The tumor-host relationship includes factors such as the histology of the primary tumor, disease free interval and the doubling time of the tumor.

Other important factors in determining the operability include the number, size, and location of the metastasis.

Survival benefits from surgery depend on a careful selection of the patient and stratifying the risk factors associated with the tumor-host relationship.

The primary site must be controlled locally with no evidence of active disease.

There must be no evidence of extrathoracic metastatic disease. However, involvement of other extrathoracic sites may not be a contraindication to the resection of the pulmonary disease as long as all disease sites can be resected completely before the lung resection.

All pulmonary metastases must be resectable.

The patient must have an adequate pulmonary reserve to tolerate the pulmonary resection.

Most patients are asymptomatic (85%), and the diagnosis of pulmonary metastases is usually made in the context of staging and follow-up of a primary extrathoracic malignancy.

The computed tomography (CT) scan is the gold standard for the evaluation of pulmonary metastases.

With standard CT techniques using collimations of 1 cm, the risk of underestimating the number of metastases is 35% to 40%. The risk of overestimating the lesions is 25% to 30%. Therefore, accurate information is only obtained in about 70% to 75% of patients. When CT is used to look for metastatic disease, collimations of 5 mm or less should be used because this increases the accuracy of the preoperative evaluation.

A single pulmonary lesion in a patient with a previous history of malignancy cannot be assumed to be metastasis unless properly investigated. This requires getting a tissue diagnosis. A solitary pulmonary nodule is likely to be a metastasis in 60% to 80% of patients with a prior history of sarcoma or melanoma, in 50% of patients with prior adenocarcinoma, and in less than 20% of patients with prior squamous cell or prostatic carcinoma.

Some primary tumors when metastatic to the lung can also spread to local and regional lymph nodes. Typical examples are colon and renal cell carcinoma. In these patients, the preoperative evaluation should also include a search for such nodes in the hilum or the mediastinum.

The indication for surgery in patients with the suspicion of lymph node involvement is not clear. Enlarged lymph nodes can be biopsied by mediastinoscopy or by endobronchial ultrasound–guided biopsy. If the patient suffers from a single metastatic disease with lymph nodes in one station only, a case can be done to resect all visible disease.

All patients with pulmonary metastases should also have a careful search for any occult extrathoracic metastases, particularly to the liver, brain, and the retroperitoneum.

Tumor doubling time and disease-free interval must be long enough (>40 days, >2 years) to suggest slow-growing disease. However, surgery should not be denied to patients based on these criteria alone, but the prognosis will be negatively affected in those with rapid-growing tumors.

Some tumor histologies do better than others after complete resection. These tumors tend to metastasize only to the lung and include such tumors as bone and soft tissue sarcomas, as well as germ cell tumors. On the other hand melanoma and breast carcinoma tend to metastasize not only to the lung but also to other extrathoracic sites and the prognosis after lung resection is more guarded.

The extent of the disease includes the number of metastases, their size, whether they are unilateral or bilateral, and whether or not the metastases have spread to the locoregional lymph nodes. The more extensive the disease, the less is the chance to be able to obtain a complete surgical resection.

The number of metastases is usually not a limiting factor for surgery, as long as all metastases can be removed leaving the patient sufficient pulmonary function.

A trial of chemotherapy before surgery is recommended if the tumor is sensitive to the medication.

Osteosarcomas and germ cell tumors are typically treated by chemotherapy before consideration for pulmonary metastatectomy.

If effective chemotherapy is not available, visible pulmonary metastases can be used to assess the efficacy of new or experimental treatments. Alternatively, in the absence of good chemotherapy, the patient can be offered surgery. This is often the case of metastases from renal cell carcinoma.

The role of chemotherapy after surgery is not clear. Many factors are used to weigh the benefits of more chemotherapy after surgery, such as the amount of residual viable tumor in the resected metastases and the completeness of resection.

Oligometastases (<4) located in the periphery of the lung can be resected by multiple wedges by video-assisted thoracoscopic surgery (VATS). The issue with VATS is that complete palpation of the lung is more difficult with this technique. In patients with numerous small metastases, there is a strong possibility that a metastasis could be missed.

Metastatectomy should not be attempted for lesions less than 1 cm in size unless the tumor is on the surface of the lung, or tissue is needed for diagnostic or therapeutic reasons such as the determination of genetic targets. Small lesions of indeterminate etiology can be followed by serial CT scans.

Patients with initial bilateral disease can be approached by staged thoracotomies or by median or transverse sternotomy.

Larger and centrally located metastases may require a segmentectomy or a lobectomy.

Pneumonectomy is rarely indicated in the management of pulmonary metastases unless the patient can obtain an excellent prognosis after the resection or a single central lesion is causing significant problems such as pulmonary collapse or hemoptysis and the resection is done for cure. Pneumonectomy can be considered in the care of patients with central endobronchial metastases.

In patients who are not candidates for curative resection, single lesions can be treated by stereotactic radiation therapy or radio-frequency ablation.