When cells break away from a primary tumor and migrate through the body to a new location where one or more new tumors begin to form, the process known as metastasis has occurred. Generally, cancer cells are distributed in this way via the circulatory system or the closely associated lymphatic system.

Approximately 30 percent of all metastatic cancers involve one or more secondary tumors in the lungs. Some of the most common cancers that lead to secondary pulmonary tumors are breast, stomach, prostate, thyroid, colorectal, and kidney cancers, testicular teratomas, bone sarcomas, choriocarcinomas, and melanomas.

Angiogenesis (the development of capillaries) is considered one of the primary steps any tumor takes on its way to becoming dangerously malignant. Investigations of this process are ongoing, but it appears that some cancer cells are able to aggregate existing proteins in the body that facilitate angiogenesis and eventually develop to the point where they are capable of synthesizing such proteins themselves. One of these proteins facilitates the invasion of a tumor by endothelial cells. These cells accumulate and multiply to form capillaries, which are thought to promote tumor growth and cancer cell mobility.

Detection of pulmonary metastases can be very significant to a patient’s chances for survival. Treatment is most successful when there is an isolated pulmonary metastasis, which makes removal via surgery highly feasible. About half of patients with this type of metastatic disease, which is more common among those with primary tumors in breast, kidney, bone, or testicular tissue, survive more than five years if they undergo resection. Most lung metastases, however, are multiple, in which case the prognosis is not as favorable. In select patients, surgery may still be beneficial, especially if only a single lung is affected and the primary cancer is in remission.

Oftentimes patients with metastases in the lungs have not developed any symptoms of the disease at the time they are diagnosed. Instead, the thorough medical exams and advanced imaging techniques used to diagnose and stage the primary cancer frequently lead to the discovery of pulmonary metastases. In instances of slow growing primary tumors, however, metastases may be noticed before the initial disease. When symptoms of lung cancer metastasis do occur, they are similar to the signs of primary lung cancer and may include a chronic cough, chest pain, and shortness of breath.

Recent studies indicate that a new way to determine if breast cancer is likely to result in secondary tumors of the lungs may not be far off. Researchers from the Burnham Institute in La Jolla, California have identified a breast cancer cell surface molecule that is thought to arbitrate the metastasis of breast tumors. Dubbed metadherin, a name chosen to reflect the role of the molecule as a metastasis adhesion protein, the substance isolated by the investigators has been shown to specifically direct breast cancer cells to the microvasculature of the lungs, at least in early experimental work with mice. Additional research may demonstrate that antibodies directed at metadherin may reduce the likelihood of metastasis or reduce tumor growth, but in the meantime, scientists hope to be able to utilize metadherin testing to help predict the aggressiveness of breast cancers, which can greatly influence decisions regarding treatment.

Metastatic Carcinoma in Lung Tissue at 10x Magnification - The tumors that are most likely to metastasize to the lungs are those that exhibit a well-developed vasculature.

Metastatic Carcinoma in Lung Tissue at 40x Magnification - Individuals with metastases in the lungs that are considered poorly suited for surgery are usually treated with chemotherapy, though radiation therapy may also be utilized.

Metastatic Carcinoma in Lung Tissue at 10x Magnification - Carcinoma found in the lungs is more often metastatic disease rather than a primary neoplasm. This type of metastatic cancer is often more treatable than other kinds of metastases.

Metastatic Carcinoma in Lung Tissue at 4x Magnification - Since all of the body's blood circulates through the lungs, pulmonary metastases are a very common occurrence.