The short answer
Cancer spreads when cells break away from the first tumor, travel through blood or lymph, and grow in a new place. This is called metastasis.
Metastasis is when cancer cells break away and grow in a new part of the body.
Cells usually travel through the bloodstream or the lymph system.
A metastatic tumor is made of the original cancer's cells, not new local cells.
Different cancers tend to spread to certain parts of the body.
Watch: How does cancer spread?
45 sec · Captioned · What metastasis is: cells break away, travel through blood or lymph, and regrow.
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This page is for anyone who wants to understand how cancer moves from one part of the body to another, and why that changes treatment.
The simple version
Cancer starts in one place, called the primary tumor. Sometimes cells break away from it and travel to a new part of the body. There they start growing. That process is called metastasis, and the new tumors are called metastatic tumors.
How the cells travel
Cancer cells usually spread in one of two ways. They can enter the bloodstream. Or they can enter the lymph system, the network of vessels and nodes that carries immune cells. Once traveling, most cancer cells do not survive. A few can settle in a new organ and grow.
A metastatic tumor is made of the same kind of cells as the original cancer.
Why the "same cancer" rule matters
If colon cancer spreads to the liver, the new tumor is still made of colon cancer cells. Doctors call it metastatic colon cancer, not liver cancer. NCI uses the same rule for other cancers, such as metastatic breast cancer in the lung.
Why spread changes treatment
Once cancer has spread, treatment plans change. With metastatic cancer, NCI says the aim is often to control the cancer by stopping or slowing its growth rather than to cure it. Your care team can explain which treatments fit your situation. Care that eases symptoms can run alongside that treatment at any point.
Common patterns
Different cancers tend to spread to certain organs. Bone, liver, and lung are the most common sites overall. Breast cancer often spreads to bone, brain, liver, or lung. Colon cancer often spreads to the liver, lung, or peritoneum (the lining of the abdomen). Ask your care team what these patterns mean for your own situation.
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Common questions
What does metastasis mean?
Metastasis is the spread of cancer cells from the place where they first formed to another part of the body. The new tumors are called metastatic or secondary tumors.
How do cancer cells travel?
They can enter the blood or the lymph system, move to a new area, and begin to grow there. Most cells that break away do not survive the journey, but some do.
Is metastatic breast cancer a new cancer?
No. If breast cancer spreads to the lung, NCI calls it metastatic breast cancer, not lung cancer.
Can spread be found before symptoms?
Ask your care team. Which tests are used to look for spread depends on the type of cancer and your situation.
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Written by: Cancer ExplainedSources last checked: 2026-08-11 what this meansLast updated: 2026-10-16Next planned review: 2028-07-14
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Cancer Explained does not originate medical claims. Every page restates guidance already published by the National Cancer Institute, the CDC, the USPSTF and the FDA, in plain language, with the source cited so you can check the original yourself. AI does the translating and organizing; automated checks test claims, citations, clarity and safety before anything publishes, and this is translation and navigation, not clinical judgment. Nothing here is personal medical advice, and no page can account for your particular situation.
Editorial status: Source checked — This page was written with AI assistance and then compared with the sources listed on it, looking for statements those sources do not back up. That check is not a sentence-by-sentence record and can miss errors. It is not a medical review, and it does not confirm the page is complete or right for your situation.
Human medical review: not completed. Pages here are not signed off by a clinician before they publish. That is not an oversight we are quietly working around: we restate published guidance and cite it, so the authority belongs to the source rather than to us, and every page names where its claims come from — you can verify us instead of trusting us. Where a volunteer clinician has reviewed a page, their name and credentials appear on it; where no name appears, no clinician has checked it. We are glad to have reviewers and are recruiting them, and we do not hold pages back waiting for one. Use this site to understand your situation and to ask better questions of the people treating you.
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