Melanoma

Melanoma is the most serious form of skin cancer. It begins in the melanocyte cells of the skin, which are found in the bottom layer of the skin’s epidermis and in the middle layer of the eye. They produce a brown-black pigment called melanin that determines skin, hair and eye colouring. Melanin also helps protect against the damaging rays of the sun.

Melanocytes often multiply to form concentrated clusters that appear on the skin surface as small, dark, flat, or dome-shaped spots – usually harmless moles or liver spots. This happens particularly as people age. If the melanocytes multiply in a controlled and contained way, the mole is harmless (benign).

Cross section of melanocytes

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A cross section diagram of the skin showing the epidermis, dermis, and melanocytes spreading.

Rights: The University of Waikato Te Whare Wānanga o Waikato

However, sometimes, the melanocytes multiply out of control and become a malignant and life-threatening melanoma. At first, the melanoma cells just grow sideways, and so are restricted to the epidermis and to the top layers of the dermis of the skin. However, if they start to grow downwards into the dermis, the cancer will come into contact with lymph vessels and can spread through these vessels to distant sites (this spreading is called metastasis), so it is very important to remove a melanoma while it is still thin, before it penetrates to these deeper layers of the skin.

Some types of melanoma develop and thicken very quickly (over a few weeks), while others can take months or even years to develop.

The most common areas for melanoma are those exposed to the sun, but melanoma can develop in any skin type cells in the body, even areas not exposed to the sun (such as the lining of the brain, the back of the eye, underneath fingernails and toenails, or on the soles of the feet).

Melanoma on foot

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A small melanoma on a foot.

Rights: Will Blake, GNU Free Documentation Licence

How common is melanoma?

Unfortunately, New Zealand has one of the highest incidence and death rates from melanoma in the world, in 2020 we had the world's highest death rate from melanoma. In New Zealand and Australia, our incidence of melanoma is about four times as high as in Canada, the USA and the United Kingdom. In 2004 there were 1,896 melanoma registrations and 249 deaths from melanoma, in 2020 the death rate had increased to over 350 each year.

How is melanoma identified?

Melanomas usually appear as a changed mole or freckle, so if any mole or freckle changes, get it checked out. One simple way to remember the signs and symptoms of melanoma is the mnemonic ABCDE:

• Asymmetrical – the mole, freckle or lesion is not round.

• Border – the border is irregular or not well defined.

• Colour – melanomas usually have multiple colours or are dark (or have no colour at all).

• Diameter – moles greater than 5 mm are more likely to be melanomas than smaller moles.

• Evolution – any change should be looked at.

Typical melanoma

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A typical melanoma showing ABCDE features.

Rights: National Cancer Institute

Moles that develop later in life should also be looked at quickly. Most benign moles (non-malignant) have been present since childhood.

Treatment

One of the best ways to protect against the dangers of melanoma is to catch it before it’s too late. Melanoma has a high cure rate if it is caught early on. Early detection is the key to successful treatment.

Like other types of skin cancer, the most effective treatment is surgical removal. In fact, despite many years of intensive research, surgical removal of melanoma before it is 1 mm thick is the only effective cure. The thinner the melanoma, the less it has burrowed into the skin and the better the outcome. Once the melanoma has spread (metastasised), there is no effective treatment so the patient will usually die.

Chemotherapy and immunotherapy can be used and occasionally show dramatic success, but generally, the success once a melanoma has metastasised is very low. The five-year survival rate is less than 10%. The median survival is only 6–12 months.

Read about the latest research on a specific gene fault that causes a type of early-onset melanoma in this article.

Download these facts sheets (see below) from the Environmental Health Indicators Programme and Massey University, produced in 2019, for more informaton about deaths from melanoma and non-melanoma skin cancer.