| KEY POINTS |
|
Secondary lung tumours are neoplastic lesions originating at a site distinct from the primary lesion. Metastatic malignant neoplasms are the most common form of secondary lung tumours and examples include breast and colorectal cancer, melanoma and sarcoma. The most common mechanism of metastatic spread is haematogenous, via the pulmonary arteries.
The differential diagnosis of a patient with a known primary tumour and a lung nodule or mass should include secondary lung tumours, a synchronous second primary tumour and benign lesions. Spread to the lungs may also represent advanced neoplastic disease or an isolated early event.
Identifying lung metastases
Lung metastases are usually asymptomatic but may cause cough, shortness of breath or haemoptysis. Symptoms occur in up to 20 per cent of patients and depend on the proximity of the metastatic lesions to the central airways.
Secondary lung tumours may be identified following CT scanning as part of staging for malignancy. These are typically well-circumscribed, non-calcified nodules of less than 3cm seen in the peripheral lung parenchyma.1
Endotracheal and endobronchial metastases are less common. Calcified pulmonary metastases may be seen with osteogenic sarcoma, ovarian cancer, colorectal malignancy and lymphoma. Cavitation may be a feature in pulmonary metastasis of sarcomas and squamous cell carcinoma.
Improvement in the resolution of scanning allows small lesions to be identified and treatment of metastatic disease to be initiated earlier. However, the risk of false positive lesions is increased. Positron emission tomography (PET) scanning may be useful because malignant cells demonstrate increased metabolic activity. However, this activity is less likely to be apparent if lesions are less than 7mm in size. In patients with a history of sarcoma or melanoma with a solitary pulmonary nodule identified on CT, the nodule is highly likely to represent a metastasis.1 Whether it is worth obtaining tissue diagnosis depends on further management. Depending on the location of the lesion in question, percutaneous needle aspiration or bronchoscopy may avoid diagnostic surgery.
Surgery
Surgery may be indicated for patients with a pulmonary metastasis and a background of an extrapulmonary malignancy where an alternative therapy would not be effective.
Unfortunately, most solid tumours that spread to the lung are relatively insensitive to chemotherapy, so surgery may be the best option. Before a lesion in the lung is assumed to be a metastasis, it should fit the natural history of the primary tumour to metastasise predominantly to the lungs or to disseminate widely; this should also be considered when deciding on treatment.
When considering surgical treatment, the main considerations are that the primary site must be controlled, there is no systemic disease, with the exception of resectable colorectal metastases in the liver, and that all the pulmonary lesions can be removed while leaving adequate lung tissue.
The patient should be a good surgical candidate with respect to other comorbidities. Better outcomes may be achieved in patients with one or two pulmonary nodules, long tumour doubling times and long disease-free intervals. There is some evidence that the disease-free interval from the time of diagnosis of the primary cancer to the appearance of pulmonary metastasis is significant.2
Evidence for metastasectomy
More than 50 per cent of patients who undergo therapeutic pulmonary metastasectomy will experience recurrence, generally within the same lobe. This may be because CT scans underpredict the number of lesions 27–40 per cent of the time.
Despite this, it is accepted that pulmonary metastasectomy may improve survival in selected patients with favourable tumour histology compared with those who undergo incomplete resection of the lung. Pulmonary metastasectomy may also confer a survival advantage even in the case of pulmonary recurrence.2
With no randomised controlled trials, much of the evidence is based on large case series. The populations are heterogeneous, with pulmonary metastasis arising from different primary sites. In addition, different regimens of oncological treatment have been received.
The International Registry of Lung Metastases was established in 1991 to assess the long-term results of performing therapeutic resections. It included 5,206 cases of lung metastasectomy from 18 thoracic centres in Europe and the US. Single metastases accounted for 2,383 cases. The primary tumours in this study included epithelial, sarcoma, germ cell and melanoma.
Survival after complete metastasectomy was 36 per cent at five years and 26 per cent at 10 years. The corresponding values for incomplete resection were 13 and 7 per cent, respectively.
Metastasectomy methods
Where metastasectomy is indicated, a number of approaches may be used. Lung metastases may be removed by metastasectomy through a thoracotomy or video-assisted thoracoscopic surgery (VATS). Regardless of the technique, resections should always be carried out conservatively because subsequent lung resections may be necessary.3 VATS is possible if the pulmonary metastases are subpleural and are likely to be visible or palpable, and if there are only three or fewer. If, however, there are multiple lesions, thoracotomy will allow the surgeon to identify more lesions than would be seen on the CT scan.4
For bilateral lung metastases, the options include bilateral simultaneous or staged VATS or thoracotomy, or alternatively, a median sternotomy.
Some surgeons confine the use of VATS to diagnosis and staging of pulmonary disease. In 1993 the first series using VATS to perform metastasectomy was reported. In 65 of the 72 patients studied, the indication for resection was diagnosis of an indeterminate lung lesion.4
The consensus opinion is that therapeutic metastasectomy should incorporate open approaches that allow bimanual palpation of the entire lung. Therefore the role of therapeutic VATS metastasectomy is still debated.5
The follow-up of patients after pulmonary metastasectomy is controversial because there are no evidence-based guidelines. However, patients with recurrent pulmonary metastasis may benefit from further resection.
- Miss Suneeta Kochhar is senior house officer in thoracic surgery and Mrs Karen Harrison-Phipps is consultant in thoracic surgery at Guy’s Hospital, London
References
1. Rusch VW. Pulmonary metastasectomy; current indications. Chest 1995; 107(6 Suppl): 322S-331S.
2. Pastorino U, Buyse M, Friedel G et al. Long-term results of lung metastasectomy: prognostic analyses based on 5206 cases. J Thorac Cardiovasc Surg 1997; 113: 37-49.
3. Ketchedjian A, Daly B, Luketich J, Fernando H C. Minimally invasive techniques for managing pulmonary metastases: video-assisted thoracic surgery and radiofrequency ablation. Thorac Surg Clin 2006; 16: 157-65.
4. Dowling RD, Landrenean RJ, Miller DL. Video-assisted thoracoscopic surgery for resection of lung metastases. Chest 1998; 113(1 Suppl): 2S-5S.
5. Yoneda KY, Louie S, Shelton DK. Approach to pulmonary metastases. Curr Opin Pulm Med 2000; 6: 356-63.
