The epidermis has three main types of cell.
- Basal cells. These are the bottom layer of cells in the epidermis.
- Keratinocytes. These cells are in layers above the basal layer. They make a substance called keratin which is a hard 'waxy' material. Keratinocytes are constantly dividing and a certain number are dying at any given time. The top 'horny' layer of the epidermis is made of dead keratinocytes which contain keratin. The top of the skin is constantly being shed and replaced by new dead cells which contain keratin.
- Melanocytes. These cells are dotted about at the bottom of the epidermis. They make a pigment called melanin when the skin is exposed to sun. The melanin is passed to the nearby skin cells to protect them from the sun's rays. Melanin causes the skin to tan in fair skinned people. Dark skinned people have more active melanocytes.
What are cancer, skin cancer and tumours?
Cancer is a disease of the cells in the body. The body is made up from millions of tiny cells. There are many different types of cell in the body, and there are 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'.
Skin cancers are divided into:
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Melanoma ('malignant melanoma'). This type of skin cancer develops from melanocytes.
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Non-melanoma. These are divided into:
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Basal cell carcinoma (BCC) - skin cancer which develops from basal cells.
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Squamous cell carcinoma (SCC) - skin cancer which develops from keratinocytes.
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Other - other types of skin cancer are rare.
A malignant tumour is a 'lump' or 'growth' of tissue made up from cancer cells which continue to multiply. Malignant tumours invade into nearby tissues and organs which can cause damage.
Malignant tumours may also spread to other parts of the body. This happens if some cells break off from the first (primary) tumour and are carried in the bloodstream or lymph channels to other parts of the body. These small groups of cells may then multiply to form 'secondary' tumours (metastases) in one or more parts of the body. These secondary tumours may then grow, invade and damage nearby tissues, and spread again.
The rest of this page is just about melanoma. See separate page for information on non-melanoma skin cancer.
How common is melanoma?
Melanoma is not common, but the number of cases is increasing. The number of cases has about doubled in the last 20 years or so. Currently, about 7000 people develop melanoma in the UK each year. It is slightly more common in women than men. Many cases occur in older adults. However, unlike many types of cancer, a large number of cases also occur in young adults. In the UK melanoma is the third most common cancer in people aged between 15 and 40. It is rare in children, but sun damage in children is a major 'risk factor' - see below.
What causes melanoma?
A cancerous tumour starts from one abnormal cell. The exact reason why a cell becomes cancerous is unclear. It is thought that something damages or alters certain genes in the cell. This makes the cell abnormal and multiply 'out of control'. (See separate page called 'What Causes Cancer' for more details.)
Sun damage to skin
The main risk factor which damages skin and can lead to a melanoma is damage from the sun. It is the ultraviolet (UV) radiation in the sunshine which does the damage. About 6 in 10 cases of melanoma are thought to be caused by UV sun damage.
People most at risk to UV skin damage are people with fair skin. In particular those with skin which always burns and never tans, red or blond hair, green or blue eyes. Melanoma is uncommon in dark skinned people as they have more protective melatonin in their skin.
Children's skin is most vulnerable to damage. Sun exposure in childhood is the most damaging. People who had a lot of freckling in childhood, or had frequent or severe sunburn in childhood, are most at risk of developing melanoma as adults. (The damage to the skin can occur many years before a cancer actually develops.)
Melanoma is most common in fair skinned people who live in hot countries nearer to the equator. Australia and Israel have the highest rates. The rate in the USA is quite high, but decreases the further north you go in the country.
Other risk factors
Other factors which increase the risk of developing melanoma include the following.
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A family history. If a close blood relative develops melanoma then your risk is increased. This may be because you may inherit fair skin which is more easily sun damaged. However, other genetic factors are thought to play a part in some cases. Two 'faulty genes' which may be inherited have been found which are known to increase the risk or melanoma. Further research aims to clarify the role of these and other genes which may be involved. As a rule, if you have a family history of melanoma you should take extra care to protect your skin from sun damage. Also, check your skin regularly for early signs of melanoma.
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Common moles. These are the small brown marks which occur on almost everybody. They are caused by a collection of melanocytes in the skin surface. If you have many (60 or more) you have an increased risk that one will develop into a melanoma.
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Atypical (non-typical) moles. Some people have larger moles which are often irregular in shape and are usually brown or black. You have an increased risk of developing melanoma if you have one of these. In particular, if you have a strong family history of melanoma (father, mother, brother or sister with a melanoma), and you have an atypical mole, you have a very high risk of developing melanoma. Make sure you check your skin regularly.
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Using sunbeds or similar tanning machines which emit UV light.
What are the symptoms of melanoma?
A typical melanoma starts as a small dark patch on the skin. It can develop from a normal part of skin, or from an existing mole. A melanoma is often different to a mole in one or more of the following ways (summed up as ABCD) - that is:
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Asymmetry - the shape of a melanoma is often uneven and asymmetrical, unlike a mole which is usually round and even.
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Border - the border or edges of a melanoma are often ragged, notched or blurred. A mole has a smooth well-defined edge.
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Colour - the colour (pigmentation) of a melanoma is often not uniform. So there may be 2-3 shades of brown or black. A mole usually has one uniform colour.
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Diameter - the size of a melanoma is usually larger than a normal mole, and it continues to grow.
However, some melanomas are not dark, and some melanomas are not typical in how they look. As a melanoma grows in the skin it may itch, bleed, crust or ulcerate.
The 'take home message' is: see a doctor if you develop a lump or patch on the skin which you are unsure about, or if an existing mole changes in its shape, border, colour, or size. A melanoma can develop on any area of skin. Rarely, they develop in the iris or back of the eye. (Unlike non-melanoma skin cancers, melanomas often develop on areas of skin not often exposed to the sun. These areas may have had short spells of sun damage such as during a holiday.)
If some cells break off and spread (metastasize) to other parts of the body, various other symptoms can develop. A common early symptom of spread is for the nearby lymph glands (nodes) to swell.
How is a melanoma diagnosed?
If a melanoma is suspected then your doctor is likely to advise an 'excisional biopsy'. This is where the entire abnormal area of skin is removed by a minor operation. (Local anaesthetic is injected into the skin to make this painless.) This tissue is looked at under the microscope. This is to:
- Confirm the diagnosis - abnormal melanoma cells can be seen.
- To assess the thickness of the melanoma (how deep it has spread into the skin.) The thickness of the melanoma helps to guide treatment and the need for further assessment.
Initial treatment and assessment of melanoma
The excisional biopsy may be curative
When doing an excisional biopsy (described above) the doctor will remove a margin of normal skin around the melanoma. When the biopsy is looked at under the microscope, if the doctor is sure that all the melanoma cells have been removed, and the melanoma cells are confined to the top layer of skin, then no further treatment may be needed. Otherwise, a second operation called a 'wide local excision' is usually advised.
Wide local excision may be needed
This aims to remove an area of normal skin around where the melanoma had been (before it was removed with excisional biopsy). This aims to make sure that any cells which may have grown in the local area of skin have been removed. The amount of normal looking skin removed varies - depending on the thickness of the melanoma (how deep it has spread into the skin) as reported from the biopsy. It may be 1-2 cm around where the melanoma had been.
This operation may be done under local or general anaesthetic. In some cases a skin graft may be needed to cover the wound.
Staging of melanoma
The aim of staging is to find out how much a cancer has grown and spread. Finding out the stage of the cancer helps doctors to advise on the best treatment options. It also gives a reasonable indication of outlook (prognosis). (See separate page called 'Cancer Staging and Grading' for details)
The common staging system used for melanoma divides it into four stages:
- Stage one is when the melanoma is just in the top layer of skin, it is less than 1.5 mm thick, and there is no spread to anywhere else in the body.
- Stage two is when the melanoma is just in the top layer of skin but is over 1.5 mm thick, OR there are some cancer cells in nearby parts of the skin less than 5 cm away from the main (primary) tumour. There is no spread to other parts of the body.
- Stage three is when some cancer cells have spread to the nearby lymph glands (nodes), OR some cancer cells have spread to areas of nearby skin more than 5 cm away from the main tumour.
- Stage four is when some cancer cells have spread to other parts of the body such as the lung, liver, bone, etc.
Most cases of melanoma are diagnosed at stage one when there is a very good chance that treatment will cure the condition.
How is melanoma assessed and staged?
If the initial biopsy and the tissue taken from the wide local excision show that the melanoma is just in the top layer of skin and is less than 0.76 mm thick, then no further tests are usually needed. It is highly unlikely that it will have spread. This is an early stage one melanoma.
A doctor will examine you to see if you have any swollen lymph nodes (glands) near to the melanoma. If you have, then the melanoma is likely to have spread to these local lymph nodes.
It is possible that there may be some early spread without causing symptoms if the melanoma is thicker than 0.76 mm on the initial biopsy. In particular, there may be spread of some cells to the nearest lymph node without it yet causing it to swell. Therefore, a test called sentinal node biopsy, and sometimes other tests, may be advised.
Sentinal node biopsy. This is a relatively new test. The sentinel lymph node is the nearest node to the melanoma - the one likely to be first affected if cancer cells spread. A sentinel node biopsy is where this node is found, removed, and looked at under the microscope to look for cancer cells. If no cancer cells are detected, the cancer is unlikely to have spread. This test may be done at the same time as treatment with wide excision. It is done by injecting a tiny amount of radioactive liquid and coloured dye into the site of the melanoma. This travels with the lymph to the nearest (sentinel) lymph node. The node can then be detected by using x-rays and a scan for radioactivity. Once the nearest node is found, it is removed by a small operation.
Other tests. Tests which may be advised depend on: if you have symptoms; if the lymph nodes are found to be involved; the thickness of the primary melanoma (the thicker the primary tumour, the greater the chance of spread). The tests aim to detect if the cancer has spread to other parts of the body. For example, you may be advised to have x-rays, blood tests, scans, etc.
What is the treatment for melanoma?
The treatment depends on the stage.
- Stage one. A small operation to cut out the tumour (the biopsy or wide local excision described above) is usually all the treatment that is needed. This is likely to clear all the cancer cells. Following the treatment you will normally be checked from time to time to see that all is well.
- Stage two. Treatment is similar to stage one melanomas - that is a small operation is usually the main treatment. The area of skin removed will be larger than for stage one and may require a skin graft to cover the wound. Depending on the thickness of the primary tumour, you may also be offered adjuvant drug treatment (see below).
- Stage three. You will normally be offered more extensive surgery. This will usually be to remove all the local lymph nodes if the sentinal node biopsy showed cancer cells, and/or to remove other locally affected areas of skin. This aims to remove all of the cancer cells and prevent them from spreading to other parts of the body. You may also be offered adjuvant drug treatment (see below).
- Stage four. In addition to removing the primary tumour and removing affected lymph nodes, treatment will often include one or more of the following, depending on where the cancer has spread to, and what symptoms you have:
- Chemotherapy. This is a treatment which uses anti-cancer drugs to kill cancer cells, or stops cancer cells from multiplying.
- Radiotherapy. This is a treatment which uses high energy beams of radiation which are focussed on cancerous tissue. This kills cancer cells, or stops cancer cells from multiplying.
- Immunotherapy. This aims to boost the immune system to help to fight cancer.
Adjuvant treatment for stage two or three
Adjuvant means 'in addition to'. It is not clear if treatment with chemotherapy or immunotherapy is useful in addition to surgery for stage two or three. It may be that some undetected cancer cells may have spread in some cases, and adjuvant treatment may deal with these. Trials are in progress to see if the outlook (prognosis) improves for people diagnosed with stage two or three who have adjuvant treatment.
What is the outlook (prognosis)?
The outlook depends on the stage. Most cases of stage one melanoma are cured with a minor surgical operation to remove the tumour (described above). Most cases of stage two are also cured by the small operation (but slightly less than stage one).
For stage three there is still a chance of cure, but much less than for stage one or two. People with stage four melanoma (advanced melanoma) are not likely to be cured, but treatment can often slow down the progression of the cancer.
The treatment of cancer is a developing area of medicine. New treatments continue to be developed and the information on outlook above is very general. The specialist who knows your case can give more accurate information about your particular outlook, and how well your type and stage of cancer is likely to respond to treatment.
Can melanoma be prevented?
Most skin cancers (non-melanoma and melanoma skin cancers) are caused by excessive exposure to the sun. We should all limit our sun exposure in the summer months (or all year when in hot countries nearer the equator) by:
- Staying indoors or in the shade as much as possible between 11am and 3pm.
- Covering up with clothes and a wide brimmed hat when out in the sunshine.
- Applying sunscreen with a sun protection factor of 15 or more to all exposed areas of skin.
In particular, children should be protected from the sun. Sunburn or excessive exposure to the sun in childhood is thought to be the biggest risk factor to the developing of skin cancer as an adult. Also, people with a family history of melanoma should take extra care to protect their skin from the sun.
See separate page called 'Skin Cancer - Prevention' for details.
Further help and information
CancerBACUP, 3 Bath Place, Rivington Street, London, EC2A 3JR
Tel: 0808 800 1234 Web: www.cancerbacup.org.uk
Provides information and support to anyone affected by cancer.
Cancer Research UK
Their website www.cancerhelp.org.uk provides facts about cancer including treatment choices.
Wessex Cancer Trust Marc's Line
Tel (Information line): 01722 415071 Web: www.wessexcancer.org
Marc's Line (Melanoma And Related Cancers of the Skin) offers telephone advice on skin cancers.
Other support groups
See Self Help UK for a list of self help and support groups for cancer patients.
©EMIS and PIP 2004
