Lung metastasis

Metastasis is the transfer of cancer from one organ or part of the body to another. Cancer cells are able to invade the bloodstream and end up virtually anywhere in the body. A lung metastasis is therefore a secondary cancer in the lung that has spread from somewhere else.

When metastasis occurs, the lungs are frequently the destination of cancer cells, and a lung metastasis is found in one third of all patients whose cancer proves to be fatal. It is often the discovery of a lung metastasis, as a result of investigating the causes of certain symptoms, that shows that the patient already has a tumour somewhere else in the body.

The lungs are organs the functions of which are closely linked with those of many other organs, such as in the transfer of oxygen and nutrients, but this leaves them vulnerable to secondary infections of many kinds coming from other organs. They are composed of sensitive tissue that is easily damaged. These two factors make metastasis to the lungs a common event.

The primary cancer can be virtually anywhere, but the cancers that most frequently spread to the lungs are those of the breast, colon, prostate and bladder. It is also possible for a lung metastasis to come from a primary lung cancer, but this is usually only after it has spread to another organ and then back to the lungs. A metastasis can be present in the lung in a dormant state long after the primary tumour has been removed and the patient has been thought to be clear of cancer.

Much research has been done to discover why cancers spread in this way. For example, research at the Howard Hughes Medical Institute in Chevy Chase, Maryland, has suggested that a group of four genes, working together, enables cancerous cells from breast tumours to escape into the bloodstream and cause lung metastases. Shutting off all four genes at the same time has had a dramatic effect on halting not only metastasis but also the growth of the original tumour. In all, the researchers have discovered 18 genes that make a contribution to metastasis, and they have also found that targeting the proteins produced by these genes, using drugs that are already on the market, could be effective in reducing metastasis.

Another possible breakthrough has been made at the Cold Spring Harbor

Laboratory, New York, where the cells have been identified that cause a dormant lung metastasis to become aggressive, often with fatal results. These are endothelial progenitor cells, or EPCs, and they are found in the bone marrow. They provide the switch that leads to blood vessel development within a tumour, and hence its growth. Knowing the mechanism involved is a huge step forward in devising treatments that could save many lives.

The symptoms of a lung metastasis include shortness of breath, chest pain, coughing, unexplained weight loss and general weakness, all of which can be symptoms of other conditions, some of them much less serious. It is also possible for there to be no symptoms at all, and for the metastasis to be revealed during other procedures, such as a chest x-ray for another purpose.

Treatment for a lung metastasis is usually chemotherapy, as surgical removal does not guarantee that all secondary growths have been treated. As the patient’s cancer is likely to be at an advanced stage, major surgery may not be advisable in terms of the patient’s general condition. However, surgery can be an option under certain circumstances, for example when there is a good chance that all the tumours have been detected and can be removed. As mentioned above, current research provides hope of new treatments becoming available in the foreseeable future.

© John Welford