The different causes of cancer and its management
- Age, gender, genetics, and lifestyle as risk factors depend on the type
Cancer is the second most common cause of death after heart disease in most Western countries. In some countries, it is the leading cause of death. Although about 1 in 3 people in Western countries develops cancer at some stage in life, many people can be cured because of advances in diagnosis and treatment.
Many types of cancer produce a solid tumour that forms in an organ, such as the breast, intestine, or bladder. If not detected and treated, these cancers may spread to other body tissues. Other cancers are often widespread from early on, such as cancer of the lymph nodes (see Lymphoma) and cancer of blood-forming cells in the bone marrow (see Leukaemia).
What are the causes?
Cancer occurs when cells divide and grow in an uncontrolled manner. Cell division and cell functioning are controlled by genes, and defects in some of these genes can lead to a cell becoming cancerous. In both children and adults, these defects (mutations) in the genes may be caused by environmental factors such as chemicals (especially from smoking), viruses, ultraviolet light, or other types of radiation. In some cases, an abnormal gene is inherited from a parent. The main causes of cancer vary in different age groups.
Children and adults with reduced immunity, such as those with AIDS (see HIV infection and AIDS) or people who are taking immunosuppressants, have an increased risk of developing certain types of cancer. In such people, agents such as viruses are more likely to cause cancer.
Cancer in children
Cancers in children are rare, affecting about 1 in 500 children under the age of 15 in the UK, but they are still a major cause of death in infancy. The most common childhood cancers are leukaemia and tumours of the brain and spinal cord (see Brain and spinal cord tumours in children).
The cause of most types of cancer in children is not known. Some cancers, such as a neuroblastoma, occur primarily in children. A neuroblastoma develops in an adrenal gland or the nervous system from tissue that normally disappears during fetal development. Cancers of this type are most common during infancy. Other types of childhood cancer, such as primary bone cancer, affect older children.
Occasionally, cancer is due to an inherited abnormal gene or genes. About half of all cases of the eye cancer retinoblastoma are mainly genetic in origin, and kidney cancer (see Wilms’ tumour) sometimes runs in families. In such cases, one or more family members may have the same cancer.
The risk of cancer is increased in some genetic disorders. For example, children with Down’s syndrome are 10–20 times more likely than other children to develop leukaemia.
Some cancers in children may be caused by environmental factors. For example, certain viruses, such as the Epstein–Barr virus, are known to cause some types of cancer, including one type of childhood lymphoma.
Cancer in adults
Cancer occurs much more commonly in adults than in children. In the UK, about 1 in 3 people develops cancer at some time in adult life. The most common types of cancer that occur in adults are lung cancer, skin cancer, breast cancer, colorectal cancer, and prostate cancer.
Many cancers in adults under the age of 40 have a significant inherited factor. Up to 1 in 10 cases of cancer of the ovary, breast cancer, prostate cancer, and colorectal cancer are due in part to inheritance of abnormal genes. In older people, a combination of several factors eventually leads to cancer. The most common factors are carcinogens (cancer-causing agents), which include certain chemicals (particularly those found in tobacco smoke), dietary factors, some viruses, and specific types of radiation, including the ultraviolet light in natural sunlight.
In adults over the age of 50, the total number of newly diagnosed cancer cases roughly doubles each decade. Therefore, an 80-year-old person is eight times more likely to have cancer than a 50-year-old person. Some cancers, such as certain types of skin cancer and prostate cancer, are very common in old age, but these cancers may often be present without causing serious problems.
What are the symptoms?
Sometimes, a cancer is detected before it causes symptoms, often during a routine screening test. However, cancer is more often discovered when symptoms gradually develop and become noticeable over a period of weeks or months, prompting a person to visit a doctor. The symptoms of cancer may include:
A lump, which is often firm and painless, in or beneath the skin.
Changes in the appearance of a mole.
A nonhealing wound.
Blood in the urine or sputum.
Changes in bowel habits.
A discharge containing blood from the rectum or vagina.
Persistent abdominal pain.
Hoarseness or changes in the voice.
Difficulty with swallowing.
Severe, recurrent headaches.
Many cancers also produce more general symptoms, which may include:
Loss of appetite and nausea.
If you experience one or more of these symptoms, you should consult your doctor as soon as possible.
How is it diagnosed?
Routine screening is constantly improving the early diagnosis of cancer. Screening aims to detect disease before symptoms are present. An example is examination of the large intestine, such as a colonoscopy or a rectal examination, to look for colorectal cancer. Other screening tests that are commonly used include mammography to check for breast cancer and the cervical smear test to look for precancerous cells that may lead to cancer of the cervix.
Alternatively, cancer may be diagnosed as a result of tests to investigate symptoms. Such tests may include imaging tests, such as X-rays, ultrasound scanning, CT scanning, or MRI. In a few cases, blood tests may be performed. For example, one test looks for proteins that indicate a particular type of tumour. To confirm a diagnosis, it is usually necessary to have a biopsy, in which a sample of abnormal tissue is removed and tested to find out if cancer is present. If cancer is present, further tests will identify the type of cell in the tissue that has become cancerous, which can give an indication of how fast the tumour is likely to grow and the best way to treat it. Once a diagnosis of cancer has been made, you will probably have tests to investigate how far the cancer has spread from its original site (see Staging cancer).
What are the treatments?
Although cancer can develop at many different sites around the body, the general principles of treatment are the same. The chances of a cancer being curable are highest if it is detected by screening at a sufficiently early stage before it causes symptoms.
Depending on the type and the stage of cancer, treatment may be intended to cure the cancer, slow the growth of the cancer, or be palliative (in which treatment is intended to help a person live as comfortably as possible rather than attempt to cure the cancer).
In most cases, curative treatment involves the surgical removal of a tumour. In addition to surgery, nonsurgical treatments, such as chemotherapy and radiotherapy, are often given with the aim of destroying any cancer cells that have spread beyond the obvious solid tumour. Nonsurgical treatments may also be used if a cure is not possible with the aim of slowing the growth of certain types of cancer rather than curing them. Palliative care can control the symptoms of cancer, maximize quality of life, and provide psychological help for you and your family as you come to terms with the process of dying. Palliative care may also prolong life, although that is not its primary aim.
Treatment is tailored to the type and the extent of the cancer, your age, your general health, and your wishes after discussing the outlook and options with doctors and family. For example, attempts to cure a cancer may not be appropriate in extreme old age because of the adverse effects of the treatment. Instead, treatment may be offered to relieve symptoms and to improve quality of life for the time left.
Surgical removal of a tumour is the main treatment for most common solid tumours at an early stage. During surgery, it is usual to remove some normal tissue surrounding the tumour to maximize the chances that all cancerous cells are removed from the body. Sometimes, the lymph nodes near the tumour are also removed because cancer often spreads to these nodes first. Less commonly, surgery aims to remove tumours that have spread to more distant sites in the body.
Surgery may not be appropriate if a tumour is inaccessible. For example, surgery to remove a tumour deep inside the brain may cause great damage to healthy brain tissue. Surgery may also not be the best treatment if the cancer has already spread to other parts of the body. In such cases, other treatments, including chemotherapy or radiotherapy, may be appropriate.
Surgery may be used as a palliative treatment for certain types of cancer (see Palliative surgery for cancer). For example, surgery may be carried out to remove a tumour that is blocking the bowel or bile duct or to treat fractures of bones that have been weakened by cancer.
Treatment with anticancer drugs
In chemotherapy, anticancer drugs are used to kill cancerous cells. This is the principal treatment for leukaemias and other cancers that are widespread in the body. It may also be used for solid tumours that have spread to other parts of the body or to reduce the risk of further spread. Like surgery, chemotherapy may be used to cure cancer or as a palliative treatment. The side effects vary with the type of drug, but can include nausea and vomiting, temporary hair loss (see Alopecia), constipation, diarrhoea, tiredness, and rarely kidney damage or anaemia. You may be offered treatments for some of these side effects, such as antiemetic drugs for nausea and vomiting or blood transfusions for anaemia. The duration of treatment varies depending on the type of cancer and the aim of the treatment.
Treatment with radiation
In this technique, radiation is directed at cancerous cells and tissue to destroy them or slow their growth (see Radiotherapy). It may be used curatively or palliatively. Also known as radiation therapy, radiotherapy can have serious side effects, although fewer side effects are likely to occur with modern techniques because radiation can be targeted at the cancerous area more effectively, thereby reducing the amount normal tissues receive.
Fatigue is a common general effect of radiotherapy. Other side effects that may occur vary depending on the site being treated, and any area that receives a high dose of radiation will be affected. For example, radiotherapy to the breast or head often causes redness or soreness of the skin; treatment to the scalp usually causes hair loss; and radiotherapy to the abdomen or pelvis typically causes nausea, abdominal cramps, and diarrhoea. Many side effects can be relieved with drugs and clear up after the course of radiotherapy has been completed. Radiotherapy does not make the patient radioactive.
Certain types of hormone affect the cell growth and replication of some cancers. For example, the female sex hormone oestrogen is known to stimulate the growth of most breast cancers and also suppress the growth of prostate cancer. Treatment with sex hormones plays an important part in the management of these types of cancer (see Sex hormones and related drugs).
These newer types of treatment are being used increasingly to treat cancer. Unlike traditional cytotoxic drugs, which attack the cancer cells’ DNA or RNA (genetic material), biological therapies are drugs that disrupt specific biological processes of cancer cells or stimulate the immune system against the cancer (see Anticancer drugs).
Biological therapies that disrupt cancer cells’ biological processes work in various ways, depending on the specific process they affect. For example, anti-angiogenesis agents (such as bevacizumab, used to treat some cases of breast cancer) inhibit the tumours’ formation of new blood vessels, which are necessary to keep the tumours alive. Sunitinib, used to treat some kidney cancers, inhibits a specific enzyme (called tyrosine kinase) that is essential for tumour growth. Erlotinib, used to treat some cases of lung cancer, and cetuximab, used to treat some bowel cancers, block particular types of receptor (called epidermal growth factor receptors) and so prevent cancer cells with these receptors from growing.
Biological therapies that stimulate the immune system may involve taking drugs known as “cancer vaccines”. For example, substances such as interferons, which trigger some types of white blood cell to attack abnormal cells, may be manufactured synthetically and given as interferon drugs. You may also be given synthetically created anti-bodies (proteins that recognize and attack foreign cells or particles in the body) that deliver a radioactive substance or anticancer drug directly to a cancer.
Although biological therapies are being used to successfully treat an increasing range of cancers, they are not suitable in every case. Like all drug treatments, they may also cause side effects, such as fever, muscle aches, vomiting, fatigue, rash, and diarrhoea.
A diagnosis of cancer and its treatment can be stressful and frightening. The aim of supportive care is to make life continue as normally as possible. You will be offered relief for the symptoms of cancer, such as pain (see Pain relief for cancer). Side effects due to cancer treatments, such as vomiting, will also be treated. You and your family will probably be offered psychological support and advice from the medical team involved in your treatment. These specialists will help you to understand and cope with the diagnosis and treatment of the cancer. You may wish to see a counsellor to obtain advice and psychological support (see Counselling). Such support can boost your emotional wellbeing and self-esteem, which may be particularly affected if treatment has caused obvious physical changes, such as removal of a breast or hair loss. Research appears to show that people with a positive mental attitude survive longer than those who simply resign themselves to the disease.
Sharing problems with people who have had similar personal experiences can be reassuring, and it may be possible to join a support group for people with cancer and their families.
What is the prognosis?
The earlier a cancer is diagnosed, the more likely it is that treatment will be successful and the cancer can be cured. The prognosis is usually expressed in terms of a 5-year survival rate (the percentage of people alive 5 years after the diagnosis of cancer is made). For most types of cancers, the outlook has been greatly improved during the last few decades, especially in children. Even in cases where the cancer cannot be cured, there is still a good chance of long-term survival with a fairly good quality of life, often for many years after the diagnosis.
From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.
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