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Cancer Awareness GuideGeneral information & support

What is metastatic cancer? How and where cancer spreads

Hearing that a cancer has spread can be frightening, and the words used - metastatic, secondary, stage 4, advanced - can be confusing. This guide explains what they mean in general terms, so that conversations with a care team are easier to follow.

For information only - this is not medical advice. Every situation is different, and only your own medical team can explain what a diagnosis means for you. Please talk to your doctor about your questions.

What metastatic cancer means

The US National Cancer Institute (NCI) defines metastatic cancer as cancer that has spread from where it started to a distant part of the body. For many types of cancer it is also called stage 4 cancer. The process by which cancer cells spread is called metastasis (NCI: Metastatic Cancer: When Cancer Spreads). In the UK, the NHS also uses the term secondary cancer for cancer that has spread from one place to another (NHS: Cancer).

The place where the cancer first formed is called the primary cancer or primary tumour. A tumour formed by cells that have spread is a metastatic or secondary tumour.

It keeps the name of where it started

NCI explains that metastatic cancer has the same name as the primary cancer. For example, breast cancer that spreads to the lung is called metastatic breast cancer, not lung cancer, and it is treated as stage 4 breast cancer. Under a microscope and in other tests, the metastatic cells look like cells of the primary cancer, not like the cells of the organ where they are found - which is how doctors can tell the cancer has spread from somewhere else.

Sometimes doctors find metastatic cancer but cannot tell where it started. NCI calls this cancer of unknown primary origin (CUP).

How cancer spreads

According to NCI, cancer cells spread through the body in a series of steps:

  1. growing into, or invading, nearby normal tissue;
  2. moving through the walls of nearby lymph nodes or blood vessels;
  3. travelling through the lymphatic system and bloodstream to other parts of the body;
  4. stopping in small blood vessels at a distant site, and moving into the surrounding tissue;
  5. growing there until a tiny tumour forms;
  6. causing new blood vessels to grow, which gives the new tumour a blood supply.

NCI notes that most of the time, spreading cancer cells die at some point in this process. Cells that do reach a new site can also stay inactive for many years before they begin to grow again, if at all.

Where cancer tends to spread

Cancer can spread to almost any part of the body, but NCI explains that the most common sites are the bone, liver and lung, and that different cancers are more likely to spread to certain areas. Examples from NCI's table (not including lymph nodes):

  • Breast cancer: bone, brain, liver, lung.
  • Colon cancer: liver, lung, peritoneum (the lining of the abdomen).
  • Lung cancer: adrenal gland, bone, brain, liver, the other lung.
  • Prostate cancer: adrenal gland, bone, liver, lung.
  • Melanoma: bone, brain, liver, lung, skin, muscle.

Spread to nearby lymph nodes is described separately in staging. Our guide to cancer stages explained covers the TNM system, in which "M" records whether a cancer has spread to distant parts of the body.

Possible symptoms

NCI notes that metastatic cancer does not always cause symptoms. When it does, they depend on the size and location of the metastatic tumours. Examples NCI gives include:

  • pain and fractures when cancer has spread to the bone;
  • headache, seizures or dizziness when it has spread to the brain;
  • shortness of breath when it has spread to the lung;
  • jaundice (yellowing of the skin or eyes) or swelling in the belly when it has spread to the liver.

These symptoms have many other causes too. After treatment, NCI suggests asking your doctor which symptoms you should report and who to call if they happen, so you know what to do if something new appears. For general signs, see cancer warning signs.

How it is found

Metastatic cancer may be found at the time of the first diagnosis, or later during follow-up. Doctors use scans, blood tests and often a biopsy, as described in how cancer is diagnosed. NCI notes that a cancer keeps the stage given at diagnosis even if it later spreads; the new information is added rather than replacing the original stage.

The aims of care

NCI states that there are treatments for most types of metastatic cancer, and that often the goal is to control the cancer by stopping or slowing its growth. NCI also notes that some people live for years with metastatic cancer that is well controlled, and that other treatments aim to improve quality of life by relieving symptoms. What is possible varies a great deal between cancer types and between people, so only your own care team can say what applies to you. Treatment choices depend on the type of primary cancer, where it has spread, previous treatments and general health. Our overview of types of cancer treatment explains the main approaches in general terms.

Palliative care - care focused on relieving symptoms and side effects and supporting quality of life - can be given at any point, alongside other treatment. NCI explains that it addresses physical, emotional, spiritual and practical needs and supports families too (NCI: Palliative Care in Cancer).

"Metastatic" and "advanced" are not quite the same

NCI describes "advanced cancer" as a broad term that can mean different things, and is often used for cancer that is unlikely to be cured. NCI adds that some advanced cancers can be controlled for many years with treatment (NCI: Advanced Cancer). If a doctor uses either word, it is reasonable to ask exactly what they mean for you.

Getting support

A diagnosis of metastatic cancer affects the whole family. Our questions to ask your doctor can help you prepare, finding trusted support lists where to turn, and how to support someone with cancer is written for family and friends. For the basics of how cancer develops, see what is cancer?

General descriptions cannot predict what will happen to any one person. Please do not use this page to interpret a scan or report - your medical team knows your full situation.

Sources

Published and last reviewed: 16 October 2026.

Common questions

Is metastatic cancer the same as stage 4?

For many types of cancer, yes. NCI explains that cancer which has spread to a distant part of the body is called metastatic cancer and, for many cancers, stage 4.

If breast cancer spreads to the bones, is it bone cancer?

No. NCI explains that metastatic cancer keeps the name of the primary cancer, so it is called metastatic breast cancer and is treated as breast cancer.

Where does cancer most often spread?

NCI lists bone, liver and lung as the most common sites, but this depends on the type of cancer, and cancer can spread to almost any part of the body.

Can metastatic cancer be treated?

NCI states there are treatments for most types of metastatic cancer, often aiming to stop or slow its growth and to relieve symptoms. What is possible differs from person to person, so ask your own care team.