The organs and tissues of the body are made up of cells. As cells age, there is a constant process of cells dying and being replaced by new cells. This is usually an orderly process, but if too many new cells are created they form a tumour.
Some tumours are not cancerous (benign) and may not need treatment, but malignant tumours (cancers) can spread.
Sometimes cells break away from the original (primary) cancer and spread to other parts of the body through the bloodstream or lymphatic system. These cells may continue to duplicate in an uncontrolled way, forming a new tumour in a different part of the body.
How common is cancer?
During our lifetimes, one in every three of us will be diagnosed with cancer, but cancer is rare in children and young people. Two-thirds of people diagnosed with cancer are aged over 65 years.
The most common cancers are breast cancer, lung cancer, bowel cancer, prostate cancer, bladder cancer, non-Hodgkin’s lymphoma, stomach cancer, melanoma, oesophageal cancer, pancreatic cancer, leukaemia and ovarian cancer. We also support people with rarer cancers. Find out more in Cancer types.
Early diagnosis makes it more likely that cancer can be treated, so it is important to be aware of possible symptoms. Many people are cured of cancer. If a cure is not possible, people with cancer can live for a long time if they have effective treatment.
Five main types of cancer
Although there are over 200 types of cancer, they can be grouped into five main types.
Carcinomas
Most cancers (85 per cent of cancers) are carcinomas. These start in the cells that line internal and external body surfaces. The commonest carcinomas are lung cancer, breast cancer and bowel cancer.
Sarcomas
Sarcomas begin in supportive tissues of the body, such as muscle, bone, cartilage, fat and connective tissue.
Leukaemias
The leukaemias are cancers of the blood cells that grow in the bone marrow, which are found in the bloodstream.
Lymphomas
Lymphomas develop in the lymph nodes and tissues of the immune system.
Adenomas
Adenomas are tumours (often benign) that begin in glandular tissue, such as the pituitary gland or thyroid.
We are here for you
Many people who have cancer, or are close to someone with cancer, find it helpful to talk to someone in a Macmillan Cancer Information and Support Service, local self help and support groups or on the Macmillan CancerLine. We are Macmillan Cancer Support: here to support anyone affected by cancer.