Metastatic lung cancer is cancer that has spread around the body. It is an advanced form of cancer that may be harder to treat. About 56 percent of lung cancers have metastasized by the time they are diagnosed. Early detection of this disease is difficult because people don’t usually develop symptoms until after lung cancer has metastasized.

What Is Metastasis?

Cancer starts with gene changes in a single cell or group of cells. Cancerous gene changes make a cell grow out of control, producing many copies of itself. When large numbers of identical cells build up in a single place, they form a tumor. The first tumor that forms in the body is called the primary tumor.

Cancer often spreads from the primary tumor to other parts of the body. This process is known as metastasis. Metastasis is also the name for a single tumor that is growing in a distant location from the primary tumor.

Cancer can metastasize from a primary tumor in the lung to faraway organs or tissues. When this metastasis happens, doctors consider the distant tumors to be lung cancer. For example, lung cancer cells that spread to the brain are lung cancer, not brain cancer. The cells look and act like lung cells and can be managed with lung cancer treatments.

How Does Metastasis Happen?

Cancer cells may metastasize by moving through the bloodstream. Other times, they travel through the lymphatic system (a network of vessels, tissues, and organs that fights infection and gets rid of waste). The process of metastasis occurs through several steps:

• The primary tumor grows into nearby tissues, such as the tissue surrounding the lung.
• Cancer cells break into the walls of a nearby lymph node or blood vessel and enter the bloodstream or lymphatic system.
• The blood or lymphatic system carries cancer cells around the body.
• Cancer cells exit through the walls of blood vessels in a new location far from the lungs.
• Cancer cells grow in this distant tissue, forming a new tumor.

Metastasis often fails. Cancer cells can die at any step along this process. However, over time, some cells will usually be successful at metastasizing.

Metastasis and Staging

Metastasis plays a large role in how a tumor is staged. Lung cancer staging is a system that describes how big tumors are and how far they have spread in the body.

One reason staging is important is that it helps doctors recommend treatment options. For example, an early-stage tumor found in a single location in the lung can often be treated with surgery. Removing the tumor and nearby tissue may be enough to treat cancer. However, people with metastatic lung cancer may have cancer cells spread throughout their bodies. In this case, doctors more often recommend systemic therapy (medication that travels throughout the bloodstream and reaches all parts of the body).

Doctors also use staging information to estimate a person’s outlook.

Lung cancer is often staged with the TNM system, which stands for tumor, nodes, and metastasis. Using this staging system, doctors score cancer within three categories. The numbers in each of these categories can tell you more about the cancer:

• Tumor — Larger T numbers mean the tumor is bigger or that it is growing into nearby tissues.
• Nodes — This score describes how many nearby or distant lymph nodes contain cancer cells.
• Metastasis — The M number says whether or not the original tumor has metastasized to other distant organs or tissues.

Doctors use TNM staging to assign lung cancer an overall stage. Non-small cell lung cancer (NSCLC) is staged on a scale from 0 to 4. Metastatic NSCLC is stage 4 (stage IV), the most advanced lung cancer stage. Small cell lung cancer (SCLC) is divided into two stages. Limited stage cancers are located in one area of the chest, and extensive-stage cancers are metastatic.

Where Does Lung Cancer Metastasize?

Doctors look for lung cancer metastases using imaging tests. These tests may include computed tomography (CT) scans or magnetic resonance imaging (MRI). Imaging tests can detect cancer cells in other locations around the body.

Lung cancer is more likely to metastasize to certain organs or tissues. The most common sites for lung cancer metastases are the bone, brain, adrenal gland, liver, and distant lymph nodes. Lung cancer can also metastasize from one lung to the other lung.

The two main types of lung cancer — non-small cell lung cancer (NSCLC) and small cell lung cancer (SCLC) — metastasize to different sites at different rates. Within each of these two main groups, different subtypes of lung cancer may be more likely to metastasize to certain tissues.

Bone Metastases

Between 22 percent and 34 percent of people with NSCLC have metastases in their bones. SCLC metastasizes to the bones in around 13 percent of cases. The bones that are most likely to be affected include the spine, ribs, hip bone, and thigh bone. Bone metastases often cause additional health problems and reduced quality of life.

Brain Metastases

Among people with NSCLC, 15 percent to 28 percent have brain metastases when diagnosed. SCLC metastasizes to this organ in about 14 percent of cases at the time of the first diagnosis. Over the course of the disease, more than 80 percent of cases of SCLC metastasize to the brain. Younger people may be slightly more likely to develop brain metastases. When lung cancer metastasizes to the brain, it can cause a poor outlook. People with brain metastases live for an average of six months after being diagnosed.

Adrenal Gland Metastases

People with NSCLC develop adrenal gland metastases about 17 percent to 37 percent of the time. Around 1 out of 5 people with SCLC have adrenal gland metastases. People with adrenal gland metastases tend to be younger than those without metastases in this area.

Adenocarcinoma, a type of NSCLC, is more likely to metastasize to the adrenal glands than other types of lung cancer. Large cell carcinoma also frequently metastasizes in the adrenal glands. People with NSCLC who have adrenal gland metastases have a worse outlook.

Liver Metastases

Liver metastasis is not as common for people with NSCLC. Around 6 percent to 13 percent of people with this type of cancer have lung cells in the liver. On the other hand, SCLC is more likely to metastasize to the liver than to any other site. Between 24 percent and 35 percent of people with SCLC have liver metastases. People with NSCLC or SCLC who have liver metastases often have a poor outlook.

Read more about liver metastasis.

Other Distant Metastasis Sites

Lung cancer can also spread to other organs or tissues at lower rates. Metastases may be found in:

• Heart muscle
• Intestines
• Stomach
• Pancreas
• Kidney
• Thyroid
• Spleen
• Ovary

Metastasizing From One Lung to the Other

For people with NSCLC, lung tumors spread to the other lung about 20 percent to 32 percent of the time. About 8 percent of people with SCLC have tumors in both lungs. People with lung metastases tend to have better survival rates than people with metastases to more distant locations.

Talk With Others Who Understand

MyLungCancerTeam is the social network for people with lung cancer and their loved ones. On MyLungCancerTeam, members come together to ask questions, give advice, and share their stories with others who understand life with lung cancer.

Are you living with metastatic lung cancer? Share your experience in the comments below, or start a conversation by posting on MyLungCancerTeam.