Melanoma in situ (stage 0 melanoma): what it means and how it is treated

Melanoma starts in melanocytes, the cells that make the pigment melanin that gives skin its natural colour. In melanoma in situ, the cancerous cells are confined to the top layer of the skin, the epidermis. The words "in situ" come from Latin and mean "in place". Cancer Research UK explains that the cells have not grown deeper, and that it is part of the number staging system that runs from stage 0 to stage 4.

Because the cells have not become invasive, some doctors call melanoma in situ a pre-cancer. The British Association of Dermatologists adds that it can be cured if it is completely removed with surgery, but that if the cells are not removed it can develop into an invasive cancer, which is why it is removed along with some surrounding healthy skin.

Lentigo maligna is a type of melanoma in situ. The University Hospitals Plymouth NHS Trust describes it as a slow-growing lesion that appears in areas of skin with a lot of sun exposure such as the face or upper body, and that it can take years to develop.

The British Association of Dermatologists says many melanomas start as minor changes in the size, shape or colour of an existing mole, while others begin as a darker area of skin that can look like a new mole. Most in situ melanomas do not cause symptoms, although tingling or itching may occur. The NHS lists changes to look out for in any mole.

• A mole with an uneven shape or edges, or two different shaped halves.

• A mix of two or more colours within a mole, such as shades of black, brown and pink.

• A larger mole, often more than 6mm across, though early melanomas can be smaller.

• A mole that changes in size, shape or colour over time.

• A mole that is swollen, sore, itchy, bleeding or crusty.

• A long-standing discoloured patch of skin on the face that slowly enlarges and develops darker areas, which is how the Plymouth leaflet describes lentigo maligna.

The NHS advises seeing a GP if you have a mole that has changed size, shape or colour, a mole that is painful, itchy, inflamed, bleeding or crusty, a new or unusual mark on your skin that has not gone away after a few weeks (including on the palms of the hands or soles of the feet), or a dark area under a nail that has not been caused by an injury. It stresses that finding a melanoma as early as possible can mean it is easier to treat.

The GP may ask to take a photograph to send to a dermatologist, which is called teledermatology, and you may get an urgent referral for more tests. The NHS says this does not definitely mean you have cancer.

The British Association of Dermatologists says that if there is doubt after a GP examination, you will be referred to a consultant dermatologist who will examine the area and decide whether it needs to be removed. The Plymouth leaflet describes an excision biopsy under local anaesthetic, in which an area of skin is taken and checked under the microscope, and a report confirms the diagnosis.

Following the biopsy, it may be necessary to have another operation, called a wider excision, in which a margin of healthy tissue is removed from around the biopsy scar to ensure that all of the lentigo maligna or melanoma in situ has been removed.

Cancer Research UK says surgery is the main treatment and that treatment also depends on where the melanoma is and your general health and level of fitness. The British Association of Dermatologists says there is no other treatment which works as well as surgery, and that usually no other tests are needed.

Occasionally a skin flap, which moves nearby skin to cover the wound, or a skin graft may be needed. Cancer Research UK adds that surgery can cause scarring and that some people may not be well enough to have an operation. Instead of surgery they might have a cream called imiquimod, applied to the affected area over a number of weeks, and you might have another skin biopsy afterwards to see if it has worked.

The British Association of Dermatologists says that following surgery you will usually be seen once in clinic to discuss the results, be shown how to carry out regular self-examination of your body, and then be discharged, in line with guidelines from the British Association of Dermatologists and NICE. The reason given is that treatment for melanoma in situ usually has a good outcome and is very unlikely to come back to the same area.

Practical effects can still be felt. The same leaflet notes that having had melanoma in situ may make it more difficult to get life or health insurance, particularly in the first five years, though some insurers are flexible once it is confirmed that it was only in situ and completely removed.

The main cause of melanoma in situ is exposure to too much ultraviolet light, especially during the first 20 years of life. The British Association of Dermatologists says that in the UK around 85 out of 100 melanomas are caused by too much UV light, that people who get a lot of sun in short bursts, such as an annual holiday, have a higher risk than those with regular sun exposure all year, and that sunbeds increase the risk even if the skin tans without burning.

Its advice after surgery is to check your skin once a month for new moles or moles that are changing, to cover up with protective clothing, to avoid the midday sun and use a high protection sun cream of at least SPF 30 with high UVA protection, and not to use sunbeds or tanning lamps. People who have had one melanoma are at an increased risk of getting another.

On the NHS the route is GP, then urgent dermatology referral, biopsy and excision, usually in dermatology or plastic surgery for sensitive sites such as the face, followed by a single review. For visible areas the NHS notes that a plastic surgeon may carry out the surgery to make sure the affected area looks as good as possible.

Some people choose a private dermatologist for quicker assessment or mole mapping. The principles are the same, because the treatment is determined by the histology report. A private team should send results to the GP and arrange wide local excision with the same margins.