What is melanoma? Symptoms, causes and treatment

What is melanoma?

Melanoma arises in melanocytes — the cells that produce melanin, the pigment that gives skin its colour. When melanocytes change and grow uncontrollably, they form a malignant tumour that can grow down into the deeper layers of the skin.

Melanoma differs from other forms of skin cancer such as basal cell carcinoma and squamous cell carcinoma in its ability to spread (metastasise) to the lymph nodes, lungs, liver and brain. That is why how deep the tumour has grown matters more than how wide it is. The depth is measured in millimetres under the microscope and is called the Breslow thickness — it is the single most important predictor of outcome.

Detected while it is still confined to the skin, melanoma has a five-year relative survival of around 99%. Once it has spread to distant organs, survival falls sharply. Nothing else you can do makes as much difference as finding it early.

Denmark has among the highest melanoma incidence rates in the world. Around 2,700–3,000 new cases are diagnosed each year, and melanoma is one of the most common cancers in Danes aged 15–34.

What does melanoma look like? The ABCDE method

The easiest way to keep an eye on your skin is to use the ABCDE method when you go through moles and new spots:

What does the ABCDE method miss?

ABCDE catches most melanomas, but not all of them. Three additional signs are worth knowing:

• The ugly duckling sign: Most people's moles look broadly alike. A mole that stands out from the rest in colour, shape or size should be checked — even if it does not tick a single ABCDE box.
• The EFG rule for nodular melanoma: Nodular melanoma grows downwards rather than outwards and is often symmetric, evenly coloured and under 6 mm — so it passes ABCDE. Use EFG instead: Elevated, Firm to the touch, and Growing continuously for more than a month.
• Amelanotic melanoma: Some melanomas contain little or no pigment. They are pink, red or skin-coloured and are easily mistaken for a harmless lump.

Beyond the ABCDE method, two patterns are worth knowing. On the face of an older adult, a slowly enlarging flat patch with uneven brown-to-black pigment on sun-damaged skin can be lentigo maligna, an early melanoma. Under a nail, a new or widening dark band running lengthwise — especially if the pigment spreads onto the surrounding skin fold (Hutchinson's sign) — can be a subungual melanoma. Both need dermatological assessment.

If you are unsure what normal looks like, compare with our guide to ordinary moles.

Why does melanoma happen?

Ultraviolet (UV) radiation from the sun is the main cause of melanoma. UV rays damage the DNA in melanocytes and can trigger uncontrolled cell division.

How do UV radiation and sunburn damage the skin?

Both UVA and UVB rays contribute to the risk. Severe sunburns — especially in childhood and the teenage years — increase the risk markedly. Years of sun exposure also show up as actinic keratoses, rough scaly patches that are themselves a marker of a heavy lifetime UV dose.

Is melanoma inherited?

Around one in ten people with melanoma has a close relative who has also had it. The inherited predisposition genes are principally CDKN2A, along with CDK4, BAP1 and POT1, plus common variants in MC1R that carry a more moderate increase in risk. Families with several cases of melanoma — or melanoma together with pancreatic cancer or mesothelioma — may be offered genetic counselling.

BRAF and NRAS are often mentioned in connection with melanoma, but these mutations are not inherited. They arise in the tumour itself and are tested for on the removed tissue to decide whether targeted drugs will work.

Do moles turn into melanoma?

Most melanomas do not begin in a mole. But people with many moles (more than 50) or with atypical moles — large, irregular moles with unclear borders, also called dysplastic naevi — carry a higher personal risk of melanoma anywhere on the skin. A high mole count is a risk marker for the person, not a queue of individual moles waiting to turn malignant.

Who gets melanoma?

Melanoma can affect anyone, but certain groups have a higher risk:

• People with fair skin: The lighter your skin and eyes, the greater the risk, because less melanin means less natural protection against UV rays.
• People with a family history: Melanoma in a parent, sibling or child increases the risk substantially.
• People with many moles: More than 50 moles, or several atypical moles, marks you out as someone who should have their skin checked regularly.
• People with a history of sunburns: Especially sunburns during childhood and the teenage years.
• People who use sunbeds: Sunbeds emit concentrated UV radiation, and the risk is greatest for those who start young.
• People with a suppressed immune system: Organ transplant recipients and others on immunosuppressive treatment have an increased risk of all skin cancers.

Melanoma also occurs in people with brown and black skin, most often as acral lentiginous melanoma on the palms, the soles of the feet or under a nail — sites that are neither sun-exposed nor routinely examined. Partly for that reason it is usually diagnosed later and has worse outcomes stage for stage.

How is melanoma diagnosed?

A dermatologist examines the lesion with a dermatoscope — a handheld magnifier with polarised light that reveals pigment patterns invisible to the naked eye. If the lesion still looks suspicious, it is removed whole (excision biopsy) and examined under the microscope. That is the only way melanoma can be confirmed or ruled out, and it is also how the Breslow thickness is measured.

A photo assessment can tell you whether a lesion looks concerning enough to be seen in person, and how quickly. It cannot rule out skin cancer. A suspicious spot needs examination with a dermatoscope and, if there is any doubt, removal of the lesion for laboratory analysis.

How is melanoma treated?

Treatment depends on how early the melanoma is found. The key to survival is early diagnosis and prompt treatment.

Frequently asked questions