How a cancer grows

This page tells you how cancers grow within the area of the body they started in. There is information on

How cancers grow locally
Where cancers spread locally

As a tumour gets bigger, it takes up more and more room in the body. Soon it begins to grow into the body structures nearby. This is called local invasion. How a cancer actually grows into surrounding normal body tissues is not fully understood. But research has pointed to 3 ways that the tumour is most likely to do this

Pressure from the growing tumour
Using enzymes
Cancer cells moving through the tissue

A particular tumour will probably use all 3 of these ways of spreading. Which way is used most will depend partly on the type of tumour, and partly on where in the body it is growing.

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. tumours may grow between sheets of muscle tissue rather than straight through one particular sheet. 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 tumour to continue to push its way through.

Using enzymes

Many normal blood cells produce chemicals called enzymes that break down cells and tissues. The blood cells use their enzymes to attack invading bacteria and viruses. They also use them to break down and clear up damaged areas in the body. The damaged cells have to be cleared away so that the body can replace them with new ones. This is all part of the natural healing process.
Many tumours contain larger amounts of these enzymes than is usual in normal tissues. It is possible that the enzymes are made and given out by the cancerous cells. But some tumours also contain a lot of normal white blood cells. They are there because they are part of the immune response of the body to the tumour. We don't know exactly where the enzymes come from. But growing tumours seem to have high levels of enzymes that break down tissue. These enzymes are likely to make it easier for the tumour to make a pathway for itself through the healthy tissue.

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 exciting because, if a substance has been found that helps cancer cells move, then research can start to find ways to stop the substance working. Research may also be able to find ways to stop the cancer cells making the substance in the first place. If cancers can be stopped from spreading, then it might be much easier to cure them.

A cancer probably just grows out in a random direction from the place where it started. However, tumours can spread into some tissues more easily than others. For example, large blood vessels that have very strong walls and dense tissues such as cartilage are hard for tumours to grow into. So locally, tumours grow along the 'path of least resistance'. This means that they probably just take the easiest route.