All cancers start when some cells in the body become abnormal and multiply faster than usual.
These cancer cells can outnumber normal cells in the area and may spread to other parts of the body.
There are many types of cancers, which behave in different ways. This is why the experience of having cancer is not the same for everyone.
Cancer is not a single disease. There are many different types of cancers. They can start almost anywhere in the body and can behave in different ways.
The cancer a person has affects:
- the symptoms they get
- the tests and treatments they need
- their chances of recovery after treatment.
How cancers start
The human body contains billions of cells which are dividing to make new cells all the time.
Sometimes there is a problem when cells divide:
- Some of the new cells are abnormal and don't behave like normal cells.
- They can grow and divide faster, or live for longer.
- The body’s immune system doesn't recognise these cells as abnormal so they keep growing.
- As more and more abnormal cells are made, they start to outnumber normal cells in the area.
- They continue to multiply out of control.
How cancers spread
Often when cancers start, they form a lump known as a tumour.
Cancers are malignant tumours, which means that can spread from where they start to other parts of the body. Some other tumours which can grow but don’t spread are known as benign tumours.
When cancers first develop and form a tumour, this is called a primary cancer.
Cells from the primary cancer can spread:
- into surrounding tissues (local spread)
- to a nearby lymph node (regional spread)
- through the bloodstream or the lymphatic system to other parts of the body (metastatic spread).
Cells that spread to other parts of the body can grow and form a new cancer. This is called a secondary cancer or a metastasis. The cells in the secondary cancer are the same type as those in the primary cancer.
Many cancers like breast, bowel and lung cancers grow and spread in this way.
Blood cells are formed through a process called haematopoiesis. This usually occurs in the bone marrow, which is a sponge-like tissue found inside many bones in the body. It may also occur in other tissues, like the spleen, liver, thymus (a gland behind the breastbone), and lymph nodes.
During this process, immature cells called haematopoietic stem cells develop into different types of blood cells.
The three main types of blood cells are:
- red blood cells
- white blood cells
Blood cancers start when a part of haematopoiesis goes wrong, and one or more cells become abnormal and start growing and dividing rapidly.
These immature abnormal blood cells crowd out normal blood cells in the bone marrow. They can also enter into the blood or lymphatic circulation and travel around the body.
The main types of blood cancer are: