Melanoma in situ
Melanoma in situ is the very earliest stage of a skin cancer called melanoma. ‘In situ’ is Latin for ‘in space’. It means that the cancer cells have not had the opportunity to spread to anywhere else in the body.
About 7,000 people in the UK are diagnosed with melanoma each year. The word ‘melanoma’ comes from the Greek word ‘melas’, meaning black. Melanin is the pigment that gives the skin its natural colour. Melanin is made in the skin by pigment cells called melanocytes. After our skin is exposed to sunlight, the melanocytes make more melanin, and so the skin becomes darker.
Melanocytes sometimes grow together in harmless groups or clusters, which are known as moles. Most people have between 10 and 50 moles and often they are darker than the surrounding skin.
Melanomas can arise in or near to a mole but can also appear on skin that looks normal. They develop when the skin pigment cells (melanocytes) become cancerous and multiply in an uncontrolled way. They can then invade the skin around them and may also spread to other areas such as the lymph nodes, liver and lungs.
In melanoma in situ, cancer cells are confined to the top layer of the skin (the epidermis) and are all contained in the area in which they began to develop. They have not started to spread or grow into deeper layers of the skin and have not become invasive. The outlook is excellent.This is because there are no blood or lymphatic channels in the top layer of the skin via which the abnormal cells can spread. Some doctors call in situ cancers ‘pre-cancer’.
Melanoma in situcan be cured if it is cut out (excised) completely. However, if not removed with appropriate surgery, it can develop into an invasive cancer. This is why it is important to have melanoma in situ removed with a small rim of normal skin (an adequate surgical margin) and to know about preventative measures you can take which will lower your risk of another melanoma in the future.