When lung cancer spreads beyond the lungs, it usually first affects nearby lymph nodes. But doctors don’t usually consider lung cancer to be “metastatic” until it has spread to more distant parts of the body.

Lung cancer can spread throughout the body in several ways. Cancerous cells can migrate to other nearby structures. They can also enter the lymphatic or circulatory system (through lymphatic and blood vessels in the lungs) and move to more distant parts of the body.

Lung cancer usually starts in the airways (bronchi and bronchioles) or air sacs (alveoli) in your lungs. Known as the parenchyma, these are the parts of your lung responsible for gas exchange — taking in oxygen and releasing carbon dioxide.

Cancer cells can migrate through these airways and spread to other areas of the lungs. This is usually the first type of “spread.” Doctors don’t consider this metastatic cancer unless the cancer has spread to the other lung.

Lung cancer can also spread to the lining of the lung, known as the pleura. However, cancer that has spread to the pleura is typically a sign of more advanced disease.

When lung cancer spreads beyond the lungs, it typically first appears in nearby lymph nodes on the same side as the original tumor site.

As cancer cells continue to spread through the lymphatic system, they may affect lymph nodes above the collarbone (just above the lungs) or on the side opposite of the tumor.

At this stage, doctors don’t consider the cancer metastasized. The American Cancer Society denotes this type of spread as “regional.”

What are signs that lung cancer has spread to the lymph nodes?

You may be able to detect swollen lymph nodes in your armpit, neck, or abdomen when lung cancer has spread there. However, these lymph nodes can swell for multiple reasons, so they’re not always a sign that cancer has spread.

A doctor can perform imaging to determine which lymph nodes have cancerous cells.

It’s easier for cancer cells to invade the lymphatic system first. However, if cancer cells invade the circulatory system, they can more quickly cause distant metastasis.

Lung cancer cells tend to spread to the:

Different types of lung cancers seem to have different preferred sites of metastasis.

The more lung cancer has spread, the less favorable your outlook. About three-quarters of lung cancers have already spread before a doctor can make a diagnosis.

Recognizing early symptoms of lung cancer may help you obtain prompt diagnosis and treatment.