How Metastatic Cancer to the Lungs Differs From Primary Lung Cancer

Symptoms, Diagnosis, Treatment, and Prognosis

Radiograph showing secondary lung cancer
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Metastatic cancer to the lungs means that cancer from another region of the body has spread to the lungs.

Another term for metastatic cancer to the lungs is secondary cancer in the lungs, as the primary cancer is the place in the body where the cancer began or originated.

For example, if breast cancer spreads to the lungs, it would be called breast cancer with metastasis to the lungs, or breast cancer with lung metastases. It wouldn't be called lung cancer because if you were to look at a metastasic tumor under a microscope, you would see that they are cancerous breast cells, not cancerous lung cells.

As an important aside, if you are looking for information on cancer which begins in the lungs and then spreads to other regions of the body, check out metastatic (stage 4) lung cancer

Overview of Metastatic Cancer to the Lungs

You may be surprised to learn that lung metastases are quite common, occurring in 30 to 55 percent of advanced cancers. While almost any cancer can spread to the lungs, some are more likely than others to do so. With that, the most common types of cancer that metastasize to the lungs include:

  • Bladder cancer
  • Breast cancer: 
  • Colon cancer
  • Kidney cancer
  • Melanoma
  • Ovarian cancer
  • Pancreatic cancer
  • Prostate cancer
  • Rectal cancer
  • Stomach cancer
  • Thyroid cancer
  • Uterine cancer

Occasionally, physicians are unable to determine where the primary site of a cancer is. In this case, they refer to the cancer as a cancer of unknown origin with metastasis to the lungs.

How Cancer Spreads

While normal cells can be thought of as being "sticky," since they have adhesion molecules that keep them in together in place, cancer cells are different. They do not make these adhesion molecules, allowing them to break free and travel as they please.

When traveling, cancer cells may extend directly to the lungs, such as cancers that begin in the esophagus or chest wall. But most cancer cells travel indirectly, through three possible ways:

  • Bloodstream (called hematogenous spread): Cancer cells may "leak" into small blood vessels near the tumors and then be carried to the lungs via the pulmonary arteries.
  • Lymphatics: Tumor cells may leak into the small lymphatic vessels and travel along the lymph pathways (including lymph nodes).
  • Pleural spread and airway spread: The pleura refers to the membranes surrounding the lung. This type of spread is often limited to lung tumors and is much less common.

Symptoms of Lung Metastases

Lung metastases often do not cause any symptoms. When this is the case, the metastases may be found on a radiological exam, like a CT scan, done to look for the presence of the spread of cancer. 

If symptoms are present, they are often similar to symptoms of primary lung cancer, like:

Since metastatic cancer implies that the primary cancer has spread through the body, general symptoms such as fatigue, unexplained weight loss, and decreased appetite are common as well.

Diagnosis of Lung Metastases

If your doctor suspects that you have lung metastases, there are several tests she may consider. These include:

  • A chest x-ray (a chest x-ray can easily miss small metastases)
  • CT scan of the chest
  • PET scan 
  • Lung biopsy (either a needle biopsy or open lung biopsy)
  • Analysis of pleural fluid if a pleural effusion is present
  • Bronchoscopy

The results of these imaging studies may provide enough evidence of metastases, although a biopsy may be needed to confirm the diagnosis.

Treatment of Lung Metastases

Treatment for cancer metastatic to the lungs is usually determined by the primary cancer or origin of the cancer. These treatments may include hormonal therapy, targeted therapies, chemotherapy, immunotherapy, or a combination of treatments.

Chemotherapy is often the treatment of choice and is usually given as palliative therapy, which is therapy given to prolong survival and decrease symptoms. Palliative therapy is not intended to cure the cancer. Even so, in rare instances, like with testicular cancer metastatic to the lungs, chemotherapy may be curative.

Occasionally, surgical treatment of lung metastases (called metastasectomy) is considered. In order for this to be effective, your doctor will want to make sure that your primary tumor is completely removed, and that all the metastases are able to be technically resected (surgically taken out). When this is the case, metastasectomy may improve your survival.

In addition to surgery, stereotactic body radiotherapy (SBRT), also referred to by terms such as "cyberknife," is sometimes used to treat metastases to the lungs from cancer in other organs.

Prognosis of Lung Metastases 

Unfortunately, cancer that has spread to the lungs (called stage 4 cancer) is usually not curable. That said, it is often very treatable, and your doctor will talk with you about treatments that may lengthen your life, as well as give you the best quality of life possible.

The survival rate, defined as the percentage of people who live five years or more after their cancer is diagnosed, varies widely depending on the primary tumor. For instance, survival is highest for tumors like testicular cancer that has spread to the lungs (73 percent 5-year survival rate) and lowest for tumors like melanoma that has spread to the lungs (15 to 20 percent 5-year survival rate).

The upside here is that it's likely that the prognosis for cancer with lung metastases will improve in the near future. Already some stage 4 cancers have responded to treatments, such as immunotherapy, in ways that were unheard of only a few years ago.

A Word From Verywell

In summary, lung metastases or metastatic cancer to the lung occurs when a cancer that originates in another area of the body, such as the breast or bladder, spreads to the lungs. Most people with lung metastases do not have symptoms, but they may experience a cough, chest pain, or hemoptysis.

Lastly, lung metastases are usually treated as part of the therapy regimen for the primary cancer, and while metastatic cancers are not usually curable (there are uncommon exceptions), treatment may both extend life and improve quality of life by controlling symptoms.

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