1

Which tumours metastasise to the lung?

The lung is the most common location for metastases for many primary cancers, with a third of all cancer patients having pulmonary metastases, at some stage.

Pulmonary metastases most commonly occur secondary to haematogenous spread and it is likely that undetected micro-metastases are already present in many patients with detectable lung metastases.

The most common primary tumours metastasising to the lungs are:

a)

colorectal carcinoma;

b)

breast carcinoma;

c)

renal cell carcinoma;

d)

head and neck cancers.

Rarer tumours where the lung is the most likely location for metastatic disease include:

a)

malignant melanoma;

b)

bone and soft tissue sarcoma;

c)

malignant germ cell tumours.

Benign metastasising leiomyoma is an unusual condition in which metastatic pulmonary nodules appear in women with a history of uterine leiomyoma. The clinical course is usually indolent.

2

What is the role of the thoracic surgeon in the management of pulmonary metastases?

In selected patients, resection of pulmonary metastases may be indicated with the intention of prolonging survival.

In patients with multiple pulmonary nodules in which other diagnoses are a possibility, a video-assisted thoracoscopic surgery (VATS) lung biopsy may be indicated if the result will change management. As well as multiple pulmonary metastases (Figure 1), the differential diagnosis of multiple pulmonary nodules includes:

a)

sarcoidosis;

b)

tuberculosis;

c)

rheumatoid arthritis;

d)

benign intraparenchymal lymph nodes;

e)

granulomatosis with polyangiitis (formerly Wegener’s granulomatosis).

Occasionally, endobronchial metastases develop and endobronchial therapies, including debulking, stent deployment, laser or cryotherapy, may be required to palliate symptoms.

3

What is the rationale for pulmonary metastasectomy?

In some malignancies, there is a discrete step-wise spread to the liver and/or the lungs, whereas in others, such as primary lung cancer, pulmonary metastases are a marker of advanced systemic disease.

It has been suggested that metastasectomy surgery can improve long-term survival. For example, resection of a solitary colorectal pulmonary metastasis is associated with a 5-year-survival of up to 50%, as compared to 5% in patients with untreated Stage IV colorectal carcinoma.

The most common primary tumour considered for pulmonary metastasectomy is colorectal cancer.

Other tumour sites commonly considered include renal cell carcinoma, breast carcinoma, malignant melanoma, sarcoma and germ cell tumours.

4

What are the indications for pulmonary metastasectomy?

The indications for surgery are the same irrespective of the primary tumour site and include:

a)

fitness for surgery – which is determined by the extent of the resection and evaluated by lung function testing and assessment of comorbidities;

b)

primary tumour site is controlled;

c)

no extrapulmonary metastases are present;

d)

metastases are resectable;

e)

no non-surgical options exist with better outcomes.

In addition, the extent of lung resection needs to be considered, as performing a pneumonectomy for the control of metastatic disease can be hard to justify.

Lung-sparing techniques should be used to allow subsequent resection if further metastases develop.

5

How are pulmonary metastases detected?

As the majority of pulmonary metastases are peripheral and asymptomatic, they are usually detected on surveillance programs for the primary tumour or found incidentally.

Some patients present with symptoms, which is suggestive of more widespread or central disease. Symptoms include:

a)

cough;

b)

chest pain;

c)

shortness of breath;

d)

haemoptysis.

Some tumour sites are more likely to develop metastatic endobronchial disease than others, such as renal cell carcinoma.

Computed tomography (CT) scanning is a routine part of many cancer surveillance programs following treatment of the primary tumour and is the most common mode of detection of pulmonary metastases.

In addition to CT scanning, biomarkers are used for the surveillance of some tumour sites and may be raised in asymptomatic patients with pulmonary metastases, including:

a)

carcinoembryonic antigen (CEA) – which is expressed in 93% of patients with colorectal pulmonary metastases. Pre-operatively, a raised serum CEA (>5ng/mL) is associated with a reduced 5-year survival following pulmonary metastasectomy for colorectal cancer;

b)

α-fetoprotein (αFP) – which is associated with a poorer outcome in patients with hepatocellular carcinoma and non-seminomatous germ cell tumours;

c)

human chorionic gonadotropin (hCG) – which is associated with a poorer outcome in patients with non-seminomatous germ cell tumours.

It is likely that novel biomarkers will be developed for future clinical use and to help determine prognosis, especially as the current selection criteria for surgery (number of metastases) is too simplistic and does not necessarily reflect the tumour behaviour.

6

What imaging is required prior to pulmonary metastasectomy?

Chest radiograph (CXR) – which is a poor screening tool for detecting pulmonary metastases. Although widespread metastases (Figure 2) may be easy to appreciate on CXR, certain lesions are difficult to detect, including:

a)

apical lesions;

b)

retrocardiac lesions;

c)

small nodules throughout the lung fields.

Computed tomography (CT) scan (Figure 3) – which is the most important imaging modality, as it can:

a)

detect very small nodules (2-3mm);

b)

delineate anatomy;

c)

provide information on the possible aetiology of the nodule;

d)

detect extrapulmonary metastases;

e)

ensure that there is no local recurrence at the primary site.