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.
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.
Why the primary cancer can’t be found in CUP
The key feature of CUP is that the primary site where the cancer started can’t be found, but there is evidence of secondary cancer in the body.
There a few possible reasons for this:
- The primary cancer is too small to be found but cells from it have spread and caused secondary cancer.
- The body’s immune system killed or controlled the primary cancer but not the secondary cancer.
- The primary cancer was removed during previous surgery for something else but had already spread.