- The skin
- What is melanoma?
- How common is it?
- What are the different types of melanoma?
- What are the signs?
- What are the causes?
- Information reviewed by
The skin is the largest organ of 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.
The epidermis is the top, outer layer of the skin. It contains three main kinds of cells:
Squamous 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 the skin. Over time the body sheds these dead skin cells.
Basal cells – These block-like cells make up the lower layer of the epidermis and multiply constantly. As they age, they move up within the epidermis and flatten out to form squamous cells.
Melanocytes – These cells sit between the basal cells 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 that sits below the epidermis. It is made up of fibrous tissue and contains the roots of hair (follicles), sweat glands, blood vessels, lymph vessels, and nerves.
Melanoma is a type of skin cancer. It develops in the skin cells called melanocytes and usually occurs on parts of the body that have been overexposed to the sun. Rare melanomas can also start inside the eye or in a part of the skin or body that has never been exposed to the sun, such as the nervous system, mucous membrane (lining of the mouth, digestive tract, etc), soles of the feet, palms, and under the nails.
Although it is one of the less common types of skin cancer, melanoma is considered the most serious 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.
Australia and New Zealand have the highest rates of melanoma in the world. More than 13,000 people are diagnosed with melanoma in Australia every year. Melanoma is the third most common cancer in both men and women (excluding non-melanoma skin cancers). One in 13 men and 1 in 22 women will be diagnosed with melanoma before age 85.
Melanoma of the skin is known as cutaneous melanoma. The major subtypes are:
Superficial spreading melanoma – This makes up 55–60% of all melanomas. 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 grows on the surface of the skin, or an existing spot, freckle or mole that changes size, colour or shape. It can develop on any part of the body but especially the trunk. This type of melanoma often grows slowly and becomes more dangerous when it invades the lower layer of the skin (dermis).
Nodular melanoma – This type makes up about 10–15% of melanomas. It usually appears as a round, raised lump (nodule) on the surface of the skin that is pink, red, brown or black and feels firm to touch. It may develop a crusty surface that bleeds easily. Nodular melanoma is most commonly found in older people on 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 a rare type of melanoma (about 1–2% of all cases). It is most commonly found on the 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. It tends to grow slowly before becoming invasive.
Desmoplastic melanoma – This is another rare type of melanoma (about 1% of cases). It often appears on the head or neck of sun-damaged skin. Desmoplastic melanoma presents as a firm, growing frequently skin-coloured lump, sometimes described as scar-like. Some have a patch of overlying pigmentation, and can be difficult to diagnose.
Some rarer types of melanoma start in parts of the body other than the skin. Mucosal melanoma can start in the tissues in the mouth, anus, urethra, vagina or nasal passages. Ocular melanoma can start inside the eye. Melanoma can also start in the central nervous system.
Melanoma can vary greatly in the way it looks. In people who have lots of moles, melanoma usually stands out and looks different from the other moles. The first sign is often a new spot or occasionally a change in an existing mole:
- size – the spot may appear or begin to grow larger
- colour – the mole may become increasingly blotchy with different depths and shades of colour (brown, black, blue, red, white, light grey, pink or skin-coloured)
- shape or border – the spot may increase in height, become scaly, have an irregular shape (scalloped or notched) or lack symmetry (the halves look different)
- itching or bleeding – the mole may itch or bleed at times
- elevation – the spot may start as a raised nodule or develop a raised area, which is often reddish or reddish brown.
New moles can appear during childhood and through to the 30s and 40s, as well as during pregnancy. However, adults should see their doctor to get a new mole examined, particularly if it is noticeably different from other moles or is raised, firm and growing. Even if you have had a mole checked before and it was considered benign, it is important to regularly check your skin for any change in shape, size or colour in the future. Talk to your doctor immediately about any changes.
The main cause of all types of skin cancer 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 solariums 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 above the elbow on the arms and more than 100 on the body
- pale, fair or freckled skin, especially if it burns easily and doesn’t tan
- lots of 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
- a pattern of 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 from using immune suppression medicines for a long time.
Overexposure to UV radiation can permanently damage the skin. This damage adds up over time. Childhood exposure to UV radiation increases the risk of skin cancer later in life, although sun protection will help prevent melanoma at any age.
Family history of melanoma
Sometimes melanoma runs in families. Often, this is because family members have 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.
When two or more close relatives (parent, sibling or child) have been diagnosed with melanoma, especially if the person has been diagnosed with more than one melanoma on different areas of the skin and/or diagnosed with melanoma before the age of 40, then they may have an inherited faulty gene.
People with a strong family history of melanoma should protect and monitor their skin themselves, and have a professional skin check by a doctor every year from their early 20s. 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. Visit genetics.edu.au to find a family cancer clinic near you. To find out more, call Cancer Council 13 11 20.
This website page was last reviewed and updated November 2019.
Information reviewed by: : A/Prof Victoria Atkinson, Senior Staff Specialist, Princess Alexandra Hospital, Visiting Medical Oncologist, Greenslopes Private Hospital, and The University of Queensland Clinical School of Medicine, QLD; Adjunct Prof John Kelly AM, Consultant Dermatologist, Victorian Melanoma Service, and Department of Medicine at Alfred Health, Monash University, VIC; Dr Alex Chamberlain, Dermatologist, Glenferrie Dermatology, Victorian Melanoma Service and Monash Univeristy, VIC; Alison Button-Sloan, Melanoma Patients Australia; Peter Cagney, Consumer; Prof Brendon J Coventry, Associate Professor of Surgery, The University of Adelaide, Surgical Oncologist, Royal Adelaide Hospital, and Research Director, Australian Melanoma Research Foundation, SA; Dr David Gyorki, Consultant Surgical Oncologist, Peter MacCallum Cancer Centre, VIC; Liz King, Skin Cancer Prevention Manager, Cancer Council NSW; Shannon Jones, SunSmart Health Professionals Coordinator, Cancer Council Victoria; Caitriona Nienaber, 13 11 20 Consultant, Cancer Council WA; Prof Richard Scolyer, Senior Staff Specialist, Tissue Pathology and Diagnostic Oncology, Royal Prince Alfred Hospital, Co-Medical Director, Melanoma Institute Australia and Clinical Professor, The University of Sydney, NSW; Heather Walker, Chair, Cancer Council National Skin Cancer Committee, Cancer Council Australia.