Melanoma in situ is the earliest form of melanoma, affecting only upper layers of the skin. Long term survival approaches 100%.
Also known as
Symptoms and signs
Irregular pigmented patch of skin, usually asymmetrical in shape and structure with more than one colour and irregular borders. Melanoma in situ is usually flat.
The patch is often relatively new and growing or changing
Excessive ultraviolet exposure, especially intense sun exposure (enough to cause sunburn) during childhood or solarium use
Multiple moles, particularly dysplastic (sometimes known as atypical) moles
Previous history of any skin cancer, including melanoma, basal cell carcinoma and squamous cell carcinoma
Family history of melanoma
Prognosis / outcome
Melanoma in situ
Melanoma in situ
Melanoma in situ
Avoid excessive sun exposure. People at high risk of melanoma should have regular skin cancer examination performed by a doctor or nurse experienced in skin cancer screening.
After a diagnosis of melanoma in situ, the aim is to detect spread from the original melanoma and new melanomas at the earliest possible opportunity. People with a history of melanoma should examine their own skin regularly and have their skin examined by an experienced skin cancer doctor or other health professional - 6 monthly for 2 years, and yearly for the rest of their life. People with many moles should consider regular mole mapping photography to detect new and changing skin lesions.
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Melanoma in situ is the most common and least serious form of melanoma. It is usually easily treated by surgical removal. Long term survival approaches 100 per cent. (Warren 2008, AIHW 2016)
What is melanoma in situ?
Melanoma is an uncontrolled growth of melanocytes, the pigment producing cells in the skin. If untreated, melanoma can spread to remote sites in the body, causing serious illness or death. Melanoma in situ is melanoma in its earliest form. The "in situ" part of the name is there because at this early stage, the cancer has not spread beyond that location. It is confined to the epidermis, an upper layer of the skin, and has not yet penetrated deeper into the skin. Melanoma in situ must be diagnosed by a skin pathologist examining the cells under a microscope to examine how far into the skin the melanoma as penetrated.
Prognosis of melanoma in situ
Melanoma outcome is related to the thickness of the melanoma at the time of diagnosis. Long term survival is almost 100 per cent for melanomas less than 1mm thick (Warren 2008) Because melanoma in situ affects the top of the skin, it is the thinnest type of melanoma with the best survival rate.
Diagnosis of melanoma
Approximately half of all melanomas are detected by the patient, who brings it to the attention of a skin cancer doctor (McGuire 2011). Usually, a melanoma in situ is flat, irregularly-shaped and dark. It may have multiple colours. It is often noticed because it looks different from the person's other moles and spots.
A skin cancer doctor can diagnose melanoma by examining it closely with a dermoscope. It will usually have specific colours or structures that alert the doctor to the possibility of melanoma. Sometimes these clues to diagnosis are hard to see and the melanoma is suspected because of changed appearance in repeated dermoscopic photographs (Menzies 2018). When a melanoma is suspected, the doctor will surgically remove the suspicious spot (a procedure known as excision biopsy) so that a skin pathologist can examine the tissue and make a definite diagnosis.
Treatment of melanoma
All melanomas must be surgically removed with a clear margin around the edge. In most cases, melanoma in situ must be removed with a clear margin of at least 5mm of normal skin around its outer edge (Sladden 2018, Sladden 2020). The initial excision biopsy is rarely this wide, so usually once a melanoma in situ is detected, a further excision must be performed to ensure a clearance of at least 5mm. If the melanoma is in a cosmetically sensitive area or if the function or movement of the area is likely to be affected, your skin cancer doctor may refer you to a plastic surgeon or the melanoma unit of a hospital for further treatment.
Follow-up: what happens next?
The risk of a melanoma in situ spreading to other parts of the body is extremely low, but your doctor will perform an examination for signs that the melanoma has spread. This examination involves:
- checking the lymph glands in the neck, armpits, groin and possibly behind the knees or elbows depending on the original site of the melanoma
- checking for enlargement of, or lumps in the liver or spleen
If it has not yet been performed, your doctor should check the entire body for melanomas and other skin cancers elsewhere.
In some circumstances, your doctor may refer you to another doctor or health service for further treatment or assessment. For example:
- A plastic surgeon can perform a wider excision of the melanoma to achieve a good cosmetic outcome or preserve function of the affected area
- A public hospital melanoma unit can offer a team approach where surgeons, dermatologists, skin pathologists and other specialties are involved in your care. Your doctor may refer you to a public hospital melanoma unit for further treatment, to get a second opinion on the initial skin pathologist's report, or advice on future follow-up and treatment.
There is no evidence that blood tests, x-rays, ultrasound, lymph node biopsy or MRI scanning is helpful in detecting spread of early melanoma or influencing outcomes (Morton 2018).
Skin checks in future
Regular check-ups will help
- detect any evidence of the melanoma returning or spreading to other organs, and
- identify new melanomas.
If the original melanoma returns, it is likely to be in the first 1-2 years after diagnosis (Morton 2018). People who have had a melanoma have an increased risk — as much as 5 to 10 fold — of developing a new melanoma in future. This increased risk persists lifelong (Barbour 2019).
The usual follow-up for a patient with melanoma in situ is:
- full body skin cancer check for melanoma and other skin cancers, plus examination of lymph nodes and abdomen for signs of spread: 6-monthly for two years, then 12-monthly for the next three years and then
- a full body skin cancer check for melanoma and other skin cancers every year for life (Trotter 2013).
High risk patients
Some people have an especially high risk of developing further melanomas in future. These people include:
- People who have already had more than one melanoma
- People with a strong family history of melanoma
Mole mapping (total body photography) is sometimes recommended for people in these high risk groups (Mann 2018).
Skin cancer self-examination is a very important part of ongoing care. In people with a previous melanoma, 75 per cent of new melanomas are self-detected by the patient (Barbour 2018).
People with a history of melanoma should ideally check their own skin every 1-2 months.
Skin checks for your family
Melanoma tends to run in families. If you have had a melanoma, your first-degree relatives (children, sisters, brothers and parents) have an above-average chance of developing melanoma. They should check their own skin regularly and consider yearly skin checks by a doctor or nurse.