What is malignant melanoma?
Melanoma is a cancer which usually starts in the skin, either in a mole or in normal- looking skin. About half of all melanomas start in normal skin.
The number of people who develop melanoma is continuing to rise. More than 8,900 people in the UK are diagnosed with melanoma each year.
Melanoma is more common in women, particularly young women. In the UK itís the most common cancer in people aged 15Ė34, but like most cancers itís more usual for it to happen in older people, as our risk of cancer rises with age. Melanoma is rare in children under 14.
People with black or brown skin are much less likely to get melanoma as their skin is more naturally protected against it.
In women the most common place to develop melanoma is on the legs; in men itís on the chest or back.
How melanoma develops
Melanoma develops from melanocytes. In melanoma the melanocytes start to grow and divide more quickly than usual and start to spread into the surrounding surface layers of skin. When they grow out of control they usually look like a dark spot or mole on your skin.
Finding and treating melanoma as early as possible is very important. If a melanoma is not removed the cells can grow down deeper into the layers of the skin. These layers contain tiny blood vessels and lymph channels. Lymph channels are tiny tubes which carry lymph fluid and connect to lymph nodes (sometimes called glands) throughout the body. This is part of our immune system, which helps us to fight against infection.
If the melanoma cells go into the blood vessels or lymph channels they can travel to other parts of the body.
What is cancer?
The organs and tissues of the body are made up of tiny building blocks called cells. Cancer is a disease of these cells.
Cells in different parts of the body may look and work differently but most reproduce themselves in the same way. Cells are constantly becoming old and dying, and new cells are produced to replace them. Normally, cells divide in an orderly and controlled manner. If for some reason the process gets out of control, the cells carry on dividing, developing into a lump which is called a tumour.
Tumours can be either benign or malignant. Cancer is the name given to a malignant tumour. Doctors can tell if a tumour is benign or malignant by examining a small sample of cells under a microscope. This is called a biopsy.
In a benign tumour the cells do not spread to other parts of the body and so are not cancerous. However, if they continue to grow at the original site, they may cause a problem by pressing on the surrounding organs.
A malignant tumour consists of cancer cells that have the ability to spread beyond the original area. If the tumour is left untreated, it may spread into and destroy surrounding tissue. Sometimes cells break away from the original (primary) cancer. They may spread to other organs in the body through the bloodstream or lymphatic system.
The lymphatic system is part of the immune system - the body's natural defence against infection and disease. It is a complex system made up of organs, such as bone marrow, the thymus, the spleen, and lymph nodes. The lymph nodes (or glands) throughout the body are connected by a network of tiny lymphatic ducts.
When the cancer cells reach a new area they may go on dividing and form a new tumour. This is known as a secondary cancer or metastasis.
It is important to realise that cancer is not a single disease with a single type of treatment. There are more than 200 different kinds of cancer, each with its own name and treatment.
Types of cancer
The majority of cancers, about 85% (85 in a 100), are carcinomas. They start in the epithelium, which is the covering (or lining) of organs and of the body (the skin). The common forms of breast, lung, prostate and bowel cancer are all carcinomas.
Carcinomas are named after the type of epithelial cell that they started in and the part of the body that is affected. There are four different types of epithelial cells:
squamous cells - that line different parts of the body, such as the mouth, gullet (oesophagus), and the airways
adeno cells - form the lining of all the glands in the body and can be found in organs such as the stomach, ovaries, kidneys and prostate
transitional cells - are only found in the lining of the bladder and parts of the urinary system
basal cells - that are found in one of the layers of the skin.
A cancer that starts in squamous cells is called a squamous cell carcinoma. A cancer that starts in glandular cells is called an adenocarcinoma. Cancers that start in transitional cells are transitional cell carcinomas, and those that start in basal cells are basal cell carcinomas.
Leukaemias and lymphomas
These occur in the tissues where white blood cells (which fight infection in the body) are formed, i.e. the bone marrow and lymphatic system. Leukaemia and lymphoma are quite rare and make up about 6.5% (6.5 in 100) of all cancers.
Sarcomas are very rare. They are a group of cancers that form in the connective or supportive tissues of the body such as muscle, bone and fatty tissue. They account for less than 1% (1 in 100) of cancers.
Sarcomas are split into two main types:
bone sarcomas - that are found in the bones
soft tissue sarcomas - that develop in the other supportive tissues of the body.
Others forms of cancer
Brain tumours and other very rare forms of cancer make up the remainder of cancers.
The skin has many purposes; it:
acts as a barrier to protect the body from injury and keeps out infection keeps in necessary fluids and proteins
protects the body from the harmful effects of ultraviolet light helps to control our body temperature.
The skin is divided into two main layers. The layer nearest the surface is known as the epidermis and the layer underneath is known as the dermis.
The epidermis contains three types of cells. On the surface are flat cells, known as squamous cells. Under the layer of squamous cells are rounder cells called basal cells. In between the basal cells are melanocytes.
The dermis contains nerve endings, blood vessels, and oil and sweat glands. Itís held together by a protein called collagen.
Structure of the skin
Melanocytes are cells which produce a pigment called melanin. Melanin is responsible for the natural colour of our skin and protects it from the harmful effects of the sun. Melanocytes are found in the lower part of the epidermis.
When our skin is exposed to a lot of sun our melanocytes increase the amount of melanin to absorb more ultra violet rays. This makes the skin darker and gives it a suntanned appearance. A suntan is a sign that the skin has been damaged and is trying to protect itself.
People with brown or black skin have the same number of melanocytes but make more melanin. This means that they have more natural protection from the sunís ultra violet rays.
Moles (sometimes called naevi) are just a group or cluster of melanocytes that lie close together. Most people with white skin have about 10Ė50 moles on their skin. Some young adults can have as many as 100.
Types of melanoma
Here are the four main types of skin (cutaneous) melanoma:
Superficial spreading melanoma is the most common type of skin melanoma. In women the most common place for it to start is on the legs, while in men itís on the chest and the back. At first the melanoma cells usually grow slowly, spreading out across the surface of the skin.
Nodular melanoma is the second most common type, but most thin melanomas arenít nodular melanomas. It can grow more quickly than other melanomas and is usually found on the chest, back, head or neck.
Lentigo maligna melanoma is usually found in older people, in areas of skin that have had a lot of exposure to the sun over many years (most often the face and neck). It develops from a slow growing precancerous condition called a Hutchisonís freckle, which looks like a stain on the skin.
Acral melanoma is the rarest type and is usually found on the palms of the hands, soles of the feet, under nails or toenails. Itís more common in people with black or brown skin and isnít thought to be related to sun exposure.
Rarely melanoma can start in parts of the body other than the skin.