This leaflet gives a general overview of cancer. Other leaflets in this series provide details of different types of cancer, treatments, and other related topics.
Cancer is a disease of the cells in the body. There are many different types of cell in the body, and many different types of cancer which arise from different types of cell. What all types of cancer have in common is that the cancer cells are abnormal and multiply out of control. Some cancers are more serious than others, some are more easily treated than others (particularly if diagnosed at an early stage), some have a better outlook (prognosis) than others.
So, cancer is not just one condition. In each case it is important to know exactly what type of cancer has developed, how large it has become, whether it has spread, and how well it usually responds to treatment.
The body is made up from millions of tiny cells. Different parts of the body such as organs, bones, muscles, skin, and blood are made up from different specialised cells. All cells have a centre called a nucleus. The nucleus in each cell contains thousands of genes which are made up from a chemical called DNA. The genes are like codes which control the functions of the cell. For example, different genes control how the cell makes proteins, or hormones, or other chemicals. Certain genes control when the cell should multiply, and certain genes even control when the cell should die.
Most types of cell in the body divide and multiply from time to time. As old cells wear out or become damaged, new cells are formed to replace them. Some cells normally multiply quickly. For example, you make millions of red blood cells each day as old ones become worn out and are broken down. Some cells do not multiply at all once they are mature - for example, brain cells. Normally, your body only makes the right number of cells that are needed.
Sometimes a cell becomes abnormal. This occurs because one (or more) gene in the cell becomes damaged or altered. The abnormal cell may then divide into two, then four, then eight, and so on. Lots of abnormal cells may then develop from the original abnormal cell. These cells do not know when to stop multiplying. A group of abnormal cells may then form. If this group of cells gets bigger, it becomes a large clump of abnormal cells called a tumour.
A tumour is a lump or growth of tissue made up from abnormal cells. Tumours are divided into two types: benign and malignant.
These may form in various parts of the body. Benign tumours grow slowly, and do not spread or invade other tissues. They are not cancerous and are not usually life-threatening. They often do no harm if they are left alone. However, some benign tumours can cause problems. For example, some grow quite large and may cause local pressure symptoms, or look unsightly. Also, some benign tumours that arise from cells in hormone glands can make too much hormone, which can cause unwanted effects.
Malignant tumours tend to grow quite quickly, and invade into nearby tissues and organs, which can cause damage. Tumours normally develop in one original site - the primary tumour. Malignant tumours may also spread to other parts of the body to form secondary tumours (metastases). This happens if some cells break off from the primary tumour and are carried in the bloodstream or lymph channels to other parts of the body. These secondary tumours may then grow, invade and damage nearby tissues, and spread again.
Note: not all cancers form solid tumours. For example, in cancer of the blood cells (leukaemia) many abnormal blood cells are made in the bone marrow and circulate in the bloodstream.
Each cancer is thought to first start from one abnormal cell. What seems to happen is that certain vital genes which control how cells divide and multiply are damaged or altered. This makes the cell abnormal. If the abnormal cell survives it may multiply out of control into a malignant tumour.
We all have a risk of developing cancer. Many cancers seem to develop for no apparent reason. However, certain risk factors are known to increase the chance that one or more of your cells will become abnormal and lead to cancer. Risk factors include the following:
A carcinogen is something (chemical, radiation, etc) that can damage a cell and make it more likely to turn into a cancerous cell. As a general rule, the more the exposure to a carcinogen, the greater the risk. A list of known and suspected chemical carcinogens can be found at http://msds.chem.ox.ac.uk/carcinogens.html and well known examples include:
The older you become, the more likely you will develop a cancer. This is probably due to an accumulation of damage to cells in the body over time. Also, the body's defences against abnormal cells may become less good as you become older. For example, the ability to repair damaged cells, and the immune system which may destroy abnormal cells, may become less efficient with age. So, eventually one damaged cell may manage to survive and multiply out of control into a cancer. Most cancers develop in older people.
Diet and other lifestyle factors can alter the risk of developing cancer. For example:
For example, one large research study (cited below) followed up over 55,000 people for 10 years. It looked at lifestyle factors and rates of cancer. The study concluded that by following recommendations on keeping physically active, keeping weight in check, not smoking, drinking alcohol in moderation and having a healthy diet, the risk of developing bowel cancer could be reduced by as much as 23%. But, the study found that even improvement in some of these lifestyle factors had some reduction in risk.
Radiation is a carcinogen. For example, exposure to radioactive materials and nuclear fallout can increase the risk of developing leukaemia and other cancers. Too much sun exposure and sunburn (radiation from UVA and UVB) increase the risk of developing skin cancer. The larger the dose of radiation, the greater the risk of developing cancer. But note: the risk from small doses such as from a single X-ray test, is very small.
Some viruses are linked to certain cancers. For example, people with persistent infection with the hepatitis B virus or the hepatitis C virus have an increased risk of developing cancer of the liver. Another example is the link between the human papillomavirus (HPV) and cervical cancer. Most (possibly all) women who develop cervical cancer have been infected with a strain (subtype) of HPV at some point in their life. However, most viruses and viral infections are not linked to cancer.
People with a poor immune system have an increased risk of developing certain cancers. For example, people with AIDS, or people on immunosuppressive therapy.
Some cancers have a strong genetic link. For example, in certain childhood cancers the abnormal gene or genes that may trigger a cell to become abnormal and cancerous are inherited. Other types of cancer may have some genetic factor which is less clear-cut. It may be that in some people their genetic make-up means that they are less resistant to the effect of carcinogens or other factors such as diet.
Not everybody who comes into contact with a carcinogen or has an unhealthy lifestyle will develop cancer. For example, not all smokers develop cancer of the lung. In fact, we are all probably exposed to low doses of carcinogens a lot of the time.
The body has certain mechanisms that may protect us from developing cancer. For example, it is thought that many cells that are damaged by carcinogens can repair themselves. Also, the body's immune system may be able to destroy some types of abnormal cells before they multiply into a tumour. Perhaps one carcinogen may only damage one gene, and two or more genes may need to be damaged or altered to trigger the cells to multiply out of control.
In many cases it is likely that a combination of factors such as genetic make-up, exposure to a carcinogen, age, diet, the state of your immune system, etc, plays a part to trigger a cell to become abnormal, and allow it to multiply out of control into a cancer.
Your doctor will examine you to look for abnormalities such as a lump under the skin, or an enlarged liver. You may be referred for tests such as X-rays, scans, blood tests, endoscopy, bronchoscopy, etc, depending on where the suspected cancer is situated. These tests can often find the site of a suspected cancer. However, a biopsy is often needed to be certain that the abnormality is a cancer and not something else (such as a benign tumour).
A biopsy is when a small sample of tissue is removed from a part of the body. The sample is then examined under the microscope or tested in other ways to detect abnormal cells. Sometimes it is easy to obtain a biopsy. For example, from a lump on the skin which may be a skin cancer. However, it can be difficult to obtain a biopsy from deeper tissues and it may require specialised procedures.
Treatment options vary, depending on the type of cancer and how far it has grown and spread. See the separate leaflets on the specific cancers for more details. There is also another leaflet called Cancer - Staging and Grading Cancer' which discuses how a cancer is classified depending on its type (grading) and how far it has spread in the body (staging). Briefly, the three most common treatments are:
More recently, other treatments have been introduced which include:
For some cancers, a combination of two or more treatments may be used. A range of other treatments may also be used to ease cancer-related symptoms such as pain.
The aims of treatment can vary, depending on the cancer type, size, spread, etc. For example:
Therefore, it is not possible give an overall outlook (prognosis). See the information about the individual types of cancer for further details. As a general rule, the outlook is usually better the earlier a cancer is detected and treated.
If you have been diagnosed with cancer you will have many questions. The organisations listed at the bottom of the leaflet are good sources of further and detailed information. The following are also some suggested questions that you may wish to go over with your doctor:
Tel: 0808 808 0000 Web: www.macmillan.org.uk
Provides information and support to anyone affected by cancer.
Provides facts about cancer, including treatment choices.
Many cancer support groups are listed on the website of www.patient.co.uk