How cancer can spread
This page tells you about how cancers can spread. There is information about
The place where a cancer starts in the body is called the primary cancer or primary site. Cells from the primary site may break away and spread to other parts of the body. These cells can then grow and form other tumours. These are called secondary cancers or metastases.
Cancer cells can spread to other parts of the body through the bloodstream or
Cancers are named according to where they first started developing. For example, bowel cancer that has spread to the liver is called bowel cancer with liver metastases or secondaries. It is not called liver cancer. This is because the cancerous cells in the liver are cancerous bowel cells. They are not liver cells that have become cancerous.
In order to spread, some cells from the primary cancer must break away, travel to another part of the body and start growing there. Cancer cells don't stick together as well as normal cells do. They may also produce substances that stimulate them to move.
The diagram below shows a tumour in the cells lining a body structure such as the bowel wall. The tumour grows through the layer holding the cells in place (the basement membrane).
Some cells can break away and go into small lymph vessels or blood vessels called capillaries nearby.
Cancer cells can go into small blood vessels and then get into the bloodstream. They are called circulating tumour cells (or CTCs).
Researchers are looking at using circulating tumour cells to diagnose cancer instead of a tissue sample (
The circulating blood sweeps the cancer cells along until they get stuck somewhere. Often they get stuck in a very small blood vessel such as a capillary.
Then the cancer cell must move through the wall of the capillary and into the tissue of the organ close by. The cell can multiply to form a new tumour if:
- the conditions are right for it to grow
- it has the nutrients that it needs.
This is quite a complicated process and most cancer cells don't survive it. Of the many thousands of cancer cells that reach the bloodstream, only a few survive to form a secondary cancer.
Cancer cells in the circulation may try to stick to
The lymphatic system is a network of tubes and glands in the body that filters body fluid and fights infection. It also traps damaged or harmful cells such as cancer cells.
Cancer cells can go into the small lymph vessels close to the primary tumour and travel into nearby
This 2 minute video is about the lymphatic system.
Micrometastases are areas of cancer spread (metastases) that are too small to see. They are too small to show up on any type of scan.
For a few types of cancer, blood tests can detect certain proteins that the cancer cells release. These are sometimes called tumour markers. These may show that there are metastases in the body that are too small to show up on a scan. But for most cancers, there is no blood test that can say whether a cancer has spread or not.
For most cancers, doctors can only say whether it is likely or not that a cancer has spread. Doctors base this on a number of factors:
- previous experience – doctors collect and publish this information to help each other
- whether there are cancer cells in the blood vessels in the tumour removed during surgery – if cancer cells are found then the cancer is more likely to have spread to other parts of the body
gradeof the cancer (how abnormal the cells are) – the higher the grade, the more quickly the cancer grows and the more likely for cells to spread
- whether lymph nodes removed during an operation contained cancer cells – if the lymph nodes contained cancer cells this shows that cancer cells have broken away from the original cancer (but there is no way of knowing whether the cells have spread to any other areas of the body)
This information is important in treating cancer. You might have extra treatment if doctors suspect there are micrometastases. This treatment might include:
targeted treatment hormone therapy
The extra treatments might increase the chance of curing the cancer.
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