How cancers grow
This page tells you about how cancers grow. There is information about
Tumours (lumps) can be benign or cancerous (malignant). Benign means it is not cancer.
- Usually grow quite slowly
- Don't spread to other parts of the body
- Usually have a covering made up of normal cells
Benign tumours are made up of cells that are quite similar to normal cells. They will only cause a problem if they:
- grow very large
- become uncomfortable or painful
- are visible and unpleasant to look at
- press on other body organs
- take up space inside the skull (such as a brain tumour)
- release hormones that affect how the body works
Malignant tumours are made up of cancer cells. They:
- usually grow faster than benign tumours
- spread into surrounding tissues and cause damage
- may spread to other parts of the body in the bloodstream or through the lymph system to form secondary tumours. This is called metastasis
To start with, cancer cells stay within the body tissue from which they have developed – for example, the lining of the bladder or the breast ducts. Doctors call this superficial cancer growth or carcinoma in situ.
The cancer cells grow and divide to create more cells and will eventually form a tumour. A tumour may contain millions of cancer cells.
All body tissues have a layer (a membrane) that keeps the cells of that tissue inside. This is the basement membrane. Cancer cells can break through this membrane. If this happens, the cancer is called invasive.
As the tumour gets bigger, its centre gets further and further away from the blood vessels in the area where it is growing. So the centre of the tumour gets less and less oxygen and nutrients.
Like healthy cells, cancer cells cannot live without oxygen and nutrients. So they send out signals, called angiogenic factors, that encourage new blood vessels to grow into the tumour. This is called angiogenesis. Without a blood supply, a tumour can't grow much bigger than a pin head.
Once a cancer can stimulate blood vessel growth, it can grow bigger and rapidly. It stimulates the growth of hundreds of new small blood vessels (capillaries) to bring in nutrients and oxygen.
View a transcript of the video about how cancer gets a blood supply.
Research into blood vessel growth (angiogenesis)
A lot of research is going on into angiogenesis. The research so far has found that the amount of angiogenic factors is very high at the outer edges of a cancer.
Some cancer drugs can stop blood vessel growth. Doctors call these anti angiogenic drugs. These drugs can't usually get rid of a cancer completely, but may be able to shrink it or stop it growing in some cases. More of these drugs are being developed and tested all the time.
You can also find out about trials that are looking at anti angiogenic drugs on our clinical trials database.
As a tumour gets bigger, it takes up more space in the body. The cancer can then cause pressure on surrounding structures. It can also grow into body structures nearby. This is called local invasion. How a cancer actually grows into the surrounding tissues is not fully understood.
A cancer may grow out in a random direction from the place where it started. However, researchers know that tumours can spread into some tissues more easily than others. For example, large blood vessels that have strong walls and dense tissues such as cartilage are hard for tumours to grow into. So, tumours usually grow along the 'path of least resistance'. This means that they probably take the easiest route.
Research has found 3 different ways that tumours may grow into surrounding tissues. A tumour will probably use all 3 of these ways of spreading. Which way is used most depends on the type of tumour, and where in the body it is growing.
The 3 ways that tumours may grow into surrounding tissues are explained below.
Pressure from the growing tumour
As the tumour grows and takes up more space, it begins to press on the normal body tissue nearby. The tumour growth will force itself through the normal tissue, as in the diagram below.
The finger like appearance of the growth happens because it is easier for the growing cancer to force its way through some paths than others. For example, cancers may grow between sheets of muscle tissue rather than straight through the muscle.
As the cancer grows, it will squeeze and block small blood vessels in the area. Due to low blood and oxygen levels, some of the normal tissue will begin to die off. This makes it easier for the cancer to continue to push its way through.
Some normal cells produce chemicals called enzymes that break down cells and tissues. The cells use the enzymes to attack invading bacteria and viruses. They also use them to break down and clear up damaged areas in the body. This is all part of the natural healing process.
Many cancers contain larger amounts of these enzymes. Some cancers also contain a lot of normal white blood cells, which produce the enzymes. They are part of the body's immune response to the cancer. Researchers are not yet sure where the enzymes come from, but they are likely to make it easier for the cancer to spread through the healthy tissue.
As the cancer pushes through and breaks down normal tissues, it may cause bleeding due to damage to nearby blood vessels.
Cancer cells moving through the tissue
One of the things that makes cancer cells different to normal cells is that they can move about more easily. So it seems likely that one of the ways that cancers spread through nearby tissues is by the cells directly moving.
Scientists have discovered a substance made by cancer cells which stimulates them to move. They don't know for sure yet, but it seems likely that this substance plays a big part in the local spread of cancers.
This research is interesting because, if a substance can help cancer cells move, then researchers can look for ways to stop the substance working. They may also be able to find ways to stop the cancer cells making the substance in the first place.
Researchers are also trying to understand how cancer cells change shape as they move and spread to other parts of the body.
You can read about how cancer may spread to other parts of the body.