What is melanoma?
Melanoma is a type of skin cancer. It develops in the melanocytes (pigment cells) and usually occurs on parts of the body that have been overexposed to the sun.
Rare melanomas can also start in a part of the skin or body that has never been exposed to the sun, such as the nervous system, eye and mucous membrane (lining of the mouth and digestive tract), soles of the feet, palms, and under the nails.
Although one of the less common types of skin cancer, melanoma is considered the most serious type of skin cancer because it is more likely to spread to other parts of the body, especially if not detected early. The earlier melanoma is found, the more successful treatment is likely to be.
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Who gets melanoma?
Australia and New Zealand have the highest rates of melanoma in the world. More than 12,000 people are diagnosed with melanoma in Australia every year, accounting for 10% of all cancer diagnoses.
Melanoma is the third most common cancer in both men and women (excluding non-melanoma skin cancers). One in 14 men and 1 in 24 women will be diagnosed with melanoma before age 85. Although melanoma is more common in people aged over 60, it is among the five most commonly diagnosed cancers in all age groups.
Different types of melanoma
The major subtypes of skin (cutaneous) melanoma are:
Superficial spreading melanoma
This is the most common type of melanoma, making up 55–60% of all cases. It is more common in younger people and is often related to a pattern of irregular high sun exposure, including episodes of sunburn. It can start as a new brown or black spot that spreads within the outer layer of the skin (epidermis), or an existing spot, freckle or mole that changes size, colour or shape. It can develop on any part of the body. This type of melanoma often grows slowly and becomes more dangerous when it invades the lower layer of the skin (dermis).
This type makes up about 10–15% of melanomas. It usually appears as a round, raised lump on the surface of the skin that is often red, pink, brown or black and feels firm to touch. It may develop a crusty surface that bleeds easily. It is most commonly found in older people on severely sun-damaged skin on the head and neck. It is a fast-growing and aggressive form of melanoma, spreading quickly into the lower layer of the skin (dermis).
Lentigo maligna melanoma
This type of melanoma is most common in older people. It makes up about 10–15% of melanomas and begins as a large freckle (lentigo maligna) in an area of sun-damaged skin, such as the face, ears, neck and head. It may grow slowly and superficially over many years before it penetrates more deeply into the skin.
Acral lentiginous melanoma
This is an uncommon type of melanoma (around 1–2% of all cases). It is most commonly found on the hairless skin on the soles of the feet or palms of the hands, or under the fingernails or toenails. It commonly appears as a colourless or lightly pigmented area, which can be mistaken for a stain or bruise. In the nails, it most often presents as a long streak of pigment in the nail or discolouration in the skin around the nail. It may grow slowly before it becomes invasive.
This is another uncommon type of melanoma (around 1–2% of cases) that presents as a firm, progressively growing lump, often on the head or neck. Many are skin-coloured and not pigmented, and can be difficult to diagnose.
There are some other rarer types of non-skin melanoma. Mucosal melanomas start in the tissues in the mouth, nervous system, anus, urethra, vagina, and nasal passages. Ocular melanomas start in the eye. To find out more, call Cancer Council 13 11 20.
What causes melanoma?
The main risk factor associated with all types of skin cancers is overexposure to UV radiation from the sun or another source, such as solariums (tanning beds). Solariums are now banned in Australia for commercial use because research shows that people who use a solarium have a significantly greater risk of developing melanoma. When your unprotected skin is exposed to UV radiation, the structure and behaviour of the cells can change.
Anyone can develop melanoma. However, the risk is higher in people who have:
- unprotected exposure to the sun
- a history of childhood tanning and sunburn
- lots of moles (naevi) (more than 10 moles on the arms and more than 100 on the body)
- moles with an irregular shape and uneven colour (dysplastic naevi)
- a previous melanoma or other type of skin cancer
- a strong family history of melanoma
- pale, fair or freckled skin, especially if it burns easily and doesn’t tan
- experienced short, intense periods of exposure to UV radiation, such as on weekends and holidays, especially if it caused sunburn
- light-coloured eyes (blue or green), and fair or red hair
- a weakened immune system (which could be caused by having undergone immune suppression or taking certain medicines after an organ transplant)
Overexposure to UV radiation can permanently damage the skin. This damage adds up over time. Even though sun protection during childhood is very important, increased protection against sun exposure will help prevent melanoma at any age.
Find out more about protecting your skin from overexposure to the sun and sun damage.
Family history of melanoma
Sometimes melanoma runs in families. For most people this is due to having a similar skin type or a similar pattern of sun exposure in childhood. Only 1–2% of melanomas in Australia involve an inherited faulty gene. Some of these genes have been identified.
The signs that melanoma could be due to an inherited faulty gene include:
- having two or more close relatives (parent, sibling or child) who have been diagnosed with melanoma
- being diagnosed with more than one melanoma on different areas of the skin
- being diagnosed with melanoma before the age of 40.
People with a strong family history of melanoma should protect and monitor their own skin, and have a professional skin check by a doctor every year from their early twenties. New moles after this age should be investigated.
If you are concerned about your family risk factors, talk to your doctor about having regular skin checks or ask for a referral to a family cancer clinic. To find out more call Cancer Council 13 11 20.
Anatomy of the skin
The skin is the largest organ in the body. It acts as a barrier to protect the body from injury, control body temperature and prevent loss of body fluids. Skin, like all other body tissues, is made up of cells. The two main layers of the skin are the epidermis and the dermis. Below these is a layer of fatty tissue (subcutis).
The epidermis is the top, outer layer of the skin. It contains three main kinds of cells:
These flat cells are packed tightly together to make up the top layer of skin and form the thickest layer of the epidermis. These cells eventually die and become the surface of your skin. Over time our body sheds these dead skin cells.
These block-like cells make up the lower layer of the epidermis and multiply constantly. As they age, they move upwards in the epidermis and flatten out to form squamous cells.
These cells sit between the basal cells of the skin and produce a dark pigment called melanin, the substance that gives skin its colour. When skin is exposed to ultraviolet (UV) radiation, melanocytes make extra melanin to try to protect the skin from getting burnt. This is what causes skin to tan. Melanocytes are also in non-cancerous (benign) spots on the skin called moles or naevi. Most moles are brown, tan or pink in colour and round in shape.
The dermis is the layer of skin underneath the epidermis. It is made up of fibrous tissue and contains hair follicles, sweat glands, blood vessels, lymph vessels and nerves.