What is melanoma?

A melanoma is a malignant tumour (cancer) that occurs in the skin, often appearing as a new spot on normal skin, or developing from an existing mole. Risk factors for melanoma include exposure to UV radiation from sunlight (and tanning sunbeds), having severe sunburn in childhood and adolescence, and having a lot of moles on your body. If detected and treated early, most melanomas are curable.

Fair-skinned people and people with a family history of melanoma are more at risk of developing melanoma, though all ethnic groups can be affected. New Zealand has one of the highest rates of melanoma in the world.

Where does melanoma occur?

Melanoma occurs most commonly on parts of the body that have been sunburned, but it can appear in skin anywhere on the body. Melanoma develops from melanocytes, which are the cells that produce melanin, the pigment that gives skin its colour.

About your skin

The top layer of skin is called the epidermis. This layer contains basal cells, squamous cells and melanocytes. Basal and squamous cells are also called keratinocytes, because they produce keratin, the main component of skin, hair and nails.

The layer of skin underneath the epidermis is called the dermis. The dermis is composed of fibres (collagen and elastin). The dermis contains the roots of hairs, glands that make sweat and oil, blood vessels, lymph vessels and nerves.

Skin cancer formation

Like all body tissues, the skin is made of tiny ‘building blocks’ called cells. These cells can sometimes become cancerous when they have been damaged; for example, by UV (ultraviolet) radiation.

Skin cancers are named after the type of cell they begin to grow from. The three most common types of skin cancer are basal cell cancer, squamous cell cancer and melanoma.

What do melanomas look like?

Melanomas usually begin as a flat, coloured spot that changes in size, shape, or colour, or becomes raised over months. A less common type of melanoma (called nodular melanoma) is not flat, and is raised from the start. These melanomas grow quickly, are uniform in colour (have the same colour throughout), and may have no colour.

Melanoma can start in parts of the body other than the skin, but this is rare. The parts of the body that can be affected are: the eye (ocular melanoma), the mouth, vulva or vagina (mucosal melanoma), under fingernails or toenails (subungual melanoma).

Who develops melanoma?

Melanoma is most common in people with fair skin. However, people from ethnic groups with naturally darker skin, for example, Maori, Pacific and Asian peoples, can still get melanoma. Melanoma is diagnosed most often in older adults, but sometimes occurs in younger adults, and occasionally in teenagers. It is rare in children.

Risk factors for melanoma

Risk factors include:

• fair skin and red or fair hair
• one or more severe sunburns – especially in childhood and adolescence
• use of sunbeds, particularly by young people.

High-risk factors include:

• previous skin cancers, including melanoma
• a family history of melanoma (in a first-degree relative: parent, brother, sister or child)
• large, irregularly shaped and unevenly coloured moles called atypical or dysplastic naevi
• large numbers of moles.

What are the causes of melanoma?

Too much sun, especially sunburn, can cause melanoma. Each time your unprotected skin is exposed to UV radiation from the sun or other sources – such as sunbeds – the UV radiation causes changes to the structure of the cells.

Overexposure to UV radiation causes the skin to become permanently damaged. The damage worsens with more UV radiation.

Sun protection in children

The most important years for sun protection are during childhood and early adult years. Exposure to UV radiation during these years greatly increases the chance of getting melanoma later in life. Also see: Sun protection in babies and toddlers

Related topics

Also see Melanoma diagnosis and Melanoma treatment and What is cancer? 

Additional resource

The New Zealand Guidelines Group (NZGG) has a published leaflet, Melanoma - information for you, your family, whanau and friends, which is also available as a download (pdf file) from the NZGG website: www.nzgg.org.nz (see Consumer resources).

Original material provided by the Cancer Society of New Zealand, 2010. Edited by everybody, July 2010.