Cancer is a scary experience. You may have heard the term “metastasis” in relation to cancer that can spark more worry. You might not understand exactly what metastasis is. It’s the spread of cancer, from its original site,—such as when breast cancer spreads to the lungs or the brain. Read on to learn about why or how this may happen.

Two types

Two types of metastasis can occur in cancer.

• Local metastasis is exactly what it sounds like. Cancerous cells spread near the main site of cancer. For breast cancer, think of its “home” as the breast, and cancer spreads to the nearby lymph nodes. It’s like the cancer cells are going down the street to the mailbox.
• Distant metastasis is when cancer spreads far away from the home site, like in the lungs or brain. The cancer cells would have to leave “home,” (the breast) and travel far away to the lungs or the brain.

How and why it happens

How does this spread happen, you might ask. Think about tumors as vampires—they need a lot of blood to grow, and they need to find a place where the blood is full of oxygen. The lungs are just the right spot for oxygenated blood. Sometimes, cancer cells break through their home site into the bloodstream and catch a ride in the blood to the lungs. They can get stuck in the lungs and begin to grow new tumors, even though the cells are still breast cancer cells! In fact, the lungs are one of the main places of metastasis for triple negative breast cancer.

Another area of the body that needs a lot of oxygen-rich blood is the brain. This oxygen-rich blood once again comes from the lungs, and travels through the body to the brain. Some of those breast cancer cells that got stuck in the lungs continue their travels and get a lift through the bloodstream to the brain, where they grow more tumors.

Treating cancer ‘at home’ Unfortunately, cancer is extremely invasive and aggressive, especially when it starts to spread in the body. Because lung or brain metastasis of breast cancer started as breast cancer cells in the breast, it’s not the same as having lung cancer or brain cancer. Doctors refer to and treat cancer according to its home organ. Metastasis is part of the reason cancer can be so hard to treat, because treatment must target the home organ as well as where the cancer has spread to. Metastasis remains an important target for scientists to learn how to prevent, treat and cure.