types of cancer
What is cancer?
People tend to think of cancer as one particular disease but in fact there are more than 200 different kinds of cancer. What all types of cancer have in common is an abnormality of the way in which cancer cells behave. All the tissues of the body such as skin, muscle, lung etc are made up of millions of building blocks called cells. Normally these cells divide and grow in a controlled way to replace ageing tissue and replace it with new tissue. However, cancer cells divide rapidly and in an uncontrolled way that does not tend to stop unless it is treated.
In some cases these cancer cells break away from the main area of growth and spread through the blood or lymphatic (fluid drainage system) to other parts of the body where they continue to multiply. These areas are called 'metastases' or 'secondaries'. Other words that tend to be used in relation to cancer are the word 'tumour' which means an abnormal lump of tissue usually made up of cancerous cells (although occasionally the word tumour is used to mean any abnormal mass of tissue even if the cells are not cancerous) and 'malignant' which is another word for cancerous.
Why does cancer occur?
The reason why some cells become cancerous is not properly understood but a great deal of research is being done into this area. It seems that it is something to do with an alteration to, or abnormality of, the genetic blueprint called DNA inside the cells that tells the cells to continue to divide and multiply instead of switching this process off.
We do know that in some cases this DNA abnormality is inherited so, for instance, there is a degree of inheritance in some cases of bowel and breast cancer and it is also known that the cell DNA can be damaged by certain environmental factors making certain cancers more likely. For instance, certain types of skin cancer are recognised to be strongly related to over exposure to ultraviolet rays from the sun which damage the DNA in the cells, and smoking cigarettes in some way affects the cells inside the lung resulting in a higher risk of lung cancer.
However, in many cases, there is no known reason why one person develops cancer and another doesn't. In other words most cancers do not seem to have either an inherited or known environmental cause for them.
What types of cancer are there?
In theory any tissue of the body can become cancerous. However, cancer is more likely to occur in tissues that have to multiply themselves rapidly as part of normal life. For instance, skin cells have to constantly multiply to replace those that are lost from the surface of the body. Partly as a result of this and partly because the skin is exposed to ultraviolet light, skin cancer is the most common malignancy although most types of skin cancer (called non-melanoma skin cancer) are nearly always curable.
Therefore, about 85 per cent of cancers are due to malignancy of the cells that line the body (ie the skin) or the organs (such as lung lining or the tissues that line the bowel). About six per cent of cancers arise in what is called connective tissue (such as muscle, bone and fat) and about five per cent occur in the blood (leukaemia) or lymphatic system (such as a type of cancer called lymphomas). Rarer cancers make up the remainder.
The most common cancers in men are, in order: cancer of the prostate, lung cancer, bowel cancer and cancer of the bladder. In women they are: breast cancer, bowel cancer, lung cancer and cancer of the ovary.
Who gets cancer?
Anyone can get cancer. In most cases there is no particular reason why a particular person develops it. One in three of us will develop cancer at some stage. Although this sounds very frightening it must be remembered that cancer is more common in the elderly, ie we unfortunately must all die of something and heart disease and cancer are the two most common causes in developed countries. Also, not all cancers are fatal since advances in treatment mean many types of cancer can be controlled or even cured.
Obviously there are some people who are more likely to develop cancer. As mentioned, cancer is more likely to occur the older you get probably because the DNA inside the cells becomes corrupted and increasingly likely to send out the 'wrong signals' which then lead to uncontrolled cell multiplication. Exposure to certain substances also makes an individual more liable to develop certain types of cancer. Hence a cigarette smoker is at greater risk of not only lung cancer but also a large number of other cancers including cancer of the throat, stomach and tongue. People who have been exposed to asbestos are at greater risk of a type of malignancy of the lining of the lung called 'mesothelioma'. It is now well known that high doses of radiation can increase the chances of blood disorders such as leukaemia (cancer of the blood) and over exposure of the skin to the sun is a factor in the development of skin cancer.
How is cancer diagnosed?
This is a hard question to answer since, as explained above, there are many different types of cancer. It is a bit like asking 'how is illness diagnosed?' For each type of cancer there are symptoms which may cause the person to consult a doctor and for the doctor to consider cancer as a possible cause for these symptoms.
Some types of cancer are detected as part of a screening procedure. The best known of these is the national cervical smear programme which screens for early signs of abnormal cells which may lead to cervical cancer (cancer of the neck of the womb). Another example is the national breast-screening programme, which involves all women between the ages of 55 and 64 being offered a mammogram to detect early breast cancer.
If cancer is suspected the patient will almost certainly have further investigations which may include blood tests, x-rays and scans such as ultrasound, CT (computerised tomography) or MRI (magnetic resonance imaging) scans which all give images of the inside of the body. If a tumour exists, the doctors may try to obtain a biopsy (a small sample) of the tissue inside the tumour, which is then examined under a microscope to assist in diagnosis.
Further tests may be done even after a diagnosis of cancer has been made. These are often done to so-called 'stage' the cancer. Staging is now an important part of the management of many cancers and essentially means doing tests to establish how bad the cancer is both in terms of the type of cancer cells involved and how far they have spread by the time the cancer is diagnosed. This can be important both in terms of helping to decide what the best treatment regime will be and in relation to the likely outlook (prognosis) for the patient.
How is cancer treated?
There are many different treatments for cancer depending on the type of cancer involved and how far it has or has not spread at the time of diagnosis.
The main types of treatment fall into the following groups:
- hormone therapy
- gene therapy
- bone marrow and stem cell transplants.
People with certain types of cancer may have more than one of these. For instance, someone with breast cancer may have surgery to remove the breast lump, followed by chemotherapy and radiotherapy.
Each of these will be explained more fully below.
Surgery: Surgery is perhaps the oldest treatment for many cancers but it still has a large part to play in the modern treatment of many malignancies. For instance, treatment of skin cancers, bowel cancer and breast cancer usually (but not always) involves the removal of the cancer, often in association with other forms of treatment such as radiotherapy. Surgery is also sometimes used as part of the treatment of cancer recurrence (the return of cancer in an individual). For example, it is now not unusual to remove a secondary deposit in the liver from a bowel cancer by excising it, usually along with other forms of treatment.
Chemotherapy: Chemotherapy is the use of powerful drugs in order to attempt to kill the cancer cells. In the same way as radiotherapy, it may be given on its own or as one of a number of different types of treatment. It can be given to destroy the tumour, to shrink it before surgery or to reduce the chances of the cancer returning.
Chemotherapy is usually given in the form of carefully measured doses of a number of drugs given either intravenously (directly in a vein) or by mouth.
The side effects associated with chemotherapy vary according to the drugs given and alter from one individual to another. However, common side effects include nausea, hair loss (which usually recovers once the treatment is completed) and sometimes soreness of the mouth. Many of the side effects can themselves be treated with anti-sickness drugs etc.
Radiotherapy: Radiotherapy is the treatment of cancer by using high doses of x-rays directed at the cancer cells in order to kill those cells. It can be used either:
- on its own to try to destroy the cancer
- in association with chemotherapy
- to try to shrink the size of a cancerous tumour before surgery to remove it
- in an attempt to prevent the cancer cells from returning.
Radiotherapy is usually given 'externally' with the patient being given a carefully calculated dose of radiation from a machine in a special unit. However, it is occasionally given internally ie from inside the body. This can come in the form of a radioactive drink, an injection or radioactive rods or wires placed into the tumour.
Side effects of radiotherapy include general effects such as tiredness or nausea and local effects such as burning or soreness of the skin over the area exposed to the radiation.
Hormone therapy: Certain types of cancer 'feed' on the existence of particular hormones in the blood. For instance, some forms of breast cancer grow faster if the female hormone oestrogen is in the bloodstream and prostate cancer thrives if the male hormone testosterone is present. Therefore if the effect of these hormones can be blocked, this in turn slows the progression of the cancer.
One of the most successful anti cancer drugs of all time is one called tamoxifen, which acts by blocking the effect of oestrogen on breast cancer and has improved the outlook for many women with this condition. Similarly, there are a number of drugs used in the treatment of prostate cancer, such as one called goserulin that blocks the effect of testosterone on these cancer cells.
Immunotherapy: Immunotherapy is the general name given to treatment that uses or assists the body's own immune system to attack the cancer cells. It comes in many different forms. One form is a drug called interferon which is injected into the body and which 'boosts' the body's defences against certain types of cancer such as a skin cancer called malignant melanoma and cancer of the kidney.
Another type of immunotherapy that is being researched is called monoclonal antibody treatment, which is sometimes referred to in the media as the 'magic bullet'. This involves the laboratory manufacture of antibodies (substances that the body naturally produces to fight off infection) that are designed to attach themselves to certain types of cancer cells. They can either be used to attack the cancer cell or to carry a radioactive or toxic substance to the cells, which are then destroyed by the targeted radiation or toxin.
The concept of monoclonal antibody treatment is a good one but it is an area of treatment that is still being developed. It cannot be seen as a miracle cure and at the moment is only likely to be offered to a small number of carefully selected patients. It is important that someone with cancer only considers monoclonal antibody treatment on the advice of their lead specialist.
Another area of development in the field of immunotherapy is the production of vaccines to certain types of cancer. This is really a progression of the way vaccines are currently given to stimulate the body to produce its own antibodies to infection, eg the BCG vaccine to protect against tuberculosis. However, anti-cancer vaccines are still in the developmental stage.
- Gene therapy: Gene therapy is an exciting area of therapy for cancer, but one that is still only in the early stages of development. This works on the idea that, as mentioned above, cells are thought to become cancerous when part of the DNA message inside the cells becomes damaged. Gene therapy involves somehow either preventing the DNA from becoming damaged or by repairing it. One idea is to use special viruses as messengers to get inside the cells and carry a gene repair therapy with them into the cells.
- Bone marrow transplantation: Most people are familiar with the idea of organ transplantation such as kidney and heart transplants but may not know that bone marrow transplantation is also sometimes used in the treatment of certain cancers. The bone marrow is soft tissue found in the middle of many of the bones of the body and it is this that makes the blood cells.
- Bone marrow transplantation is used in blood related cancers such as in leukaemia or the lymphomas (which are a type of cancer in the lymph system).
- The transplant can either be the patient's own bone marrow that was harvested (removed) before the chemotherapy was given and which is then given back to them or can be a donor bone marrow from a relative or close genetic match.
- Stem cell transplantation: Stem cells are cells that develop into blood cells. Stem cell transplantation is similar in principal to bone marrow transplantation. High doses of cancer therapy that are toxic to the patient's bone marrow are given initially. The bone marrow can then be repopulated with healthy blood cells by giving the patient a transplant of stem cells, which were either removed from the individual before the cancer treatment or are donated by a suitable donor.
What happens if the cancer comes back
Sometimes, despite correct treatment, cancer can come back. This is called a recurrence of the cancer and can mean the cancer cells appearing either in the same place as they were originally (something called 'local recurrence') or in an area away from the original site of the cancer ('distant recurrence').
All the methods of treatment of the original cancer are sometimes used to treat the recurrence (ie surgery, chemotherapy etc) depending, of course, on the type of cancer involved and whether the specialists feel that treatment would be beneficial to the patient.
What if the cancer or the recurrence cannot be treated?
There may come a point where further treatment with the aim of curing the cancer may not be possible. However, a host of different treatments now exist with the aim of treating the symptoms of the cancer and improving the quality of life of the individual. This sort of treatment is called palliative therapy and is now a specialist area in itself with doctors and nurses who have particular training in palliative care.
How can cancer be prevented?
There is nothing an individual can do to guarantee that they will never develop cancer since, as mentioned above, the causes of most malignancies are not known. However, there are certain things that someone can do to reduce their chance of getting some types of cancer or to detect them early at a stage when treatment is likely to be more successful. These measures include:
- Not smoking, since many cancers, not only lung cancer, are related to smoking tobacco. It is important to emphasise that it is almost never too late to give up smoking since it has been shown that people who stop even well into middle age avoid most of their subsequent risk of developing lung cancer.
- Eating a healthy diet since certain malignancies such as cancer of the oesophagus (the gullet) and ovarian cancer are thought to have a link with a diet high in alcohol and fat respectively. There is also increasing evidence that healthy food such as green vegetables and fruit contain substances called anti-oxidants which have a protective effect against certain cancers. It is recommended that people eat at least five portions of fruit a day and have a diet low in fat and high in fibre.
- Avoiding over-exposure to the sun's rays to reduce the chance of developing skin cancer.
- Having regular cervical smears as part of the national cervical smear screening programme for cancer of the neck of the womb in women. This programme has been partly responsible for a fall in the number of cases and the death rate from cervical cancer.
- Attending regular mammogram appointments as arranged as part of the national breast cancer-screening programme for women. Also, all women need to be 'breast aware' and be alert to any changes in their breasts or development of breast lumps either of which should prompt medical advice.
- Regular testicular self-examination by all men so that any lumps can be reported to a doctor for further examination to exclude testicular cancer.
- Seeking medical advice for any persistent or unusual symptoms.
It is worth remembering that advances in the prevention, detection and treatment of various cancers are being made all the time which are altering the outlook for people with these conditions for the better. It has been estimated that if the current rates of improvement in survival from common cancers continues at its present rate, about 24,000 deaths within five years of diagnosis would have been avoided in patients under the age of 75 by the year 2011.
Last updated 8 August 2011