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Melanoma

Wednesday 31 October, 2012

The skin

The skin is the largest organ in the body. It covers the body, protecting it from injury, regulating its temperature and preventing it from becoming dehydrated. Skin, like all other body tissues, is made up of cells. It has two main layers called the epidermis and the dermis.

The epidermis is the top, outer layer of the skin. It contains three different kinds of cells:

squamous cells: flat cells that are packed tightly to make up the top layer
basal cells: tall cells that make up the lower layer
melanocytes: cells that produce a dark pigment called melanin, the substance that gives skin its colour.

Basal cells multiply constantly and the older cells move upwards in the epidermis. When they flatten out and form a layer they become squamous cells. The top layer of your skin is made up of dead skin cells that eventually fall off.

The dermis is the layer underneath the epidermis. It contains the roots of hairs, sweat glands, blood vessels, lymph vessels and nerves.

Melanocytes

When skin is exposed to the sun, melanocytes make extra melanin 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.

What is melanoma?

Melanoma is a type of skin cancer. There are three main types of skin cancer that are named after the cells that are affected:

squamous cell carcinoma
basal cell carcinoma
and melanoma.

Melanoma develops from melanocytes (pigment cells). It usually occurs on parts of the body that have been overexposed to the sun. However, melanoma can also start in a part of the skin or an other part of the body that's never been exposed to the sun, such as the nervous system, eye and mucous membrane (lining of the mouth and digestive tract).

Melanoma is the least common skin cancer but it's the most serious because it can spread to other parts of the body.

If found early, melanoma is often curable. If detected later, it may have grown down deeper into the dermis where it may spread.

What are the types of melanoma?

Skin melanomas are called cutaneous melanomas. Cutaneous melanomas are categorised by how thick they are, how far they've spread and the way they look.

Superficial spreading melanoma: This is the most common type of melanoma, making up almost 65% of all cases. It starts as a brown or black spot that spreads across the outer layer of the skin (epidermis). This type of melanoma becomes dangerous when it invades the lower layer of the skin (dermis).
Nodular melanoma: Makes up about 15% of melanomas. It's usually a raised lump on the surface of the skin that's very dark brownish-black or black in colour. However, nodular melanoma can sometimes be pink or red, or have no pigment at all.
Lentigo maligna melanoma (LMM): This type of melanoma is most common in older people. It makes up about 10% of melanomas. LMM begins as a large freckle (lentigo maligna) in an area of skin that's had a lot of sun exposure, such as the face, ears, neck and head. It may grow slowly and superficially over many years until it penetrates more deeply into the skin.
Acral lentiginous melanoma: A rare type of melanoma that's most commonly found on the palms of the hands, soles of the feet or under the fingernails or toenails.
Other types of melanoma: There are some other rarer types of melanoma, which start in the eyes, tissues that line the inside of the nose, anus, genital tract (urethra and vagina) and nervous system.

Melanoma in-situ

This is when the abnormal cancer cells are only in the epidermis and haven't penetrated into the dermis.

How common is melanoma?

Australia and New Zealand have the highest rates of melanoma in the world. More than 10,000 people are diagnosed with melanoma in Australia every year.

Melanoma of the skin is the fourth most common cancer in both men and women. It accounts for 10% of all cancer diagnoses. One in 19 Australians will be diagnosed with melanoma before age 85.

It's the most common type of cancer in young Australians aged 15 to 44 (20% of all cases).

What causes melanoma?

The main cause of all types of skin cancers is exposure to ultraviolet (UV) radiation from the sun or another source, such as a solarium tanning machine. Each time your unprotected skin is exposed to UV radiation, it changes the structure of cells and affects what they do.

Exposure to UV radiation permanently damages the skin. This damage adds up over time. The most important years for sun protection are during childhood. However, increased protection against sun exposure will help prevent skin cancer at whatever age it's used.

Sometimes melanoma happens by chance and isn't linked to sun exposure, but this is uncommon.

Research shows that people who first use tanning machines (solariums) before the age of 35 have an 87% higher risk of developing melanoma.

Family history of melanoma

Sometimes melanoma runs in families. For most people this is due to factors such as similar skin type or too much sun exposure in childhood. However, in a small number of people (5% to 10%), melanoma may be caused by an inherited faulty gene.

If you're concerned that you have 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 Helpline on 13 11 20.

Who is at risk?

The following factors may increase a person's risk of developing melanoma:

Skin type: Some people have skin that's more sensitive to UV radiation. This includes people who have pale or fair skin; people who burn easily and don't tan; and people with light-coloured eyes.
Having lots of moles: Adults with more than 10 moles on their arms and more than 100 on their body should have their skin checked regularly by their GP or a skin specialist (dermatologist).
Childhood tanning/sunburn: Too much sun exposure before the age of 15 greatly increases the chance of getting melanoma in later life because damaged cells have more time to develop into cancer. Studies show that people who move during adolescence from low to high UV radiation countries, such as England to Australia, develop melanoma at a lower rate than people born there.
UV exposure: People who occasionally get heavy sun exposure (e.g. on weekends or on holidays) may be more at risk, especially if they get sunburnt. People who are frequently exposed to UV rays through regular sun exposure or solarium use are also at risk.
Age: It's most common in people more than 50 years of age. However, it's the most commonly diagnosed cancer in 15 to 44 year olds.
Cancer history: A person who has had melanoma or another type of skin cancer is at an increased risk.

What are the signs and symptoms?

Melanoma can vary greatly in the way it looks. The first sign of a melanoma is usually a new spot or a change in an existing mole.

Size: The spot may begin to get, or keep getting, larger.
Colour: The mole may appear blotchy with a wide variety of colours, such as brown, black, blue, red, white and/or grey.
Shape or border: An irregular edge (scalloped or notched) or lack of symmetry is a warning sign. That is, if a line was drawn through the middle of the mole, both halves would not match up. The spot may increase in height or become scaly.
Itching or bleeding: A mole that itches from time to time or bleeds may indicate a change to melanoma.

It's normal for new moles to appear and change during childhood and pregnancy. However, all adults who have a new mole should get it examined. Even if you've had a mole checked before and it was assessed as benign, keep an eye on it because it could change in the future. Talk to your doctor immediately about any changes.

Melanoma can occur anywhere on the body. In men, it's more common on the back. Women get more melanomas on their legs.

Information reviewed by: Prof Grant McArthur, Consultant Medical Oncologist, Head of the Translational Research Group and Head of the Molecular Oncology Laboratory, Peter MacCallum Cancer Centre, VIC; Jay Allen, Consumer and Community Coordinator, Melanoma Institute Australia, NSW; Annie Angle, Cancer Council Helpline Nurse, Cancer Council Victoria; Prof Michael P Brown, Director, Cancer Clinical Trials Unit, Senior Medical Oncologist, Royal Adelaide Cancer Centre, SA; Dr Vanessa Estall, Head Radiation Oncologist, Melanoma and Skin Service, Peter MacCallum Cancer Centre, VIC; Clinton Heal, Consumer and CEO and Founder of Melanoma WA; Prof John Thompson, Professor of Melanoma and Surgical Oncology at the University of Sydney and Director, Melanoma Institute Australia, NSW; and members of the SunSmart Victoria team.