Melanoma is a type of skin cancer involving rapid and chaotic growth of melanocytes found in the epidermis of the skin . This process is triggered by a genetic transformation in the these cells either as a random occurrence or due to damage from harmful ultraviolet radiation.
Normally, melanocytes are found in the basal layer of the epidermis and produce a protein called melanin. Melanin absorbs ultraviolet radiation and thus has a protective role. Darker skinned people have the same number of melanocytes but they produce a lot more melanin than in fairer skin people. Consequently, melanoma is more prevalent, the fairer the skin. Non cancerous growth of melanocytes results in freckles, lentigos and moles (melanocytic naevi).
The significance of melanoma is that if it is detected late, it has high rates of metastasizing (spread to other areas of the body) and this process is often fatal. The most common melanoma is superficial and their growth pattern tends to be horizontal within the epidermis. With time or with further genetic transformation, the growth pattern may become more vertical with the melanoma growing down into the dermis. Melanoma may eventually travel to the lymphatics and lymph nodes before spreading to other parts of the body such as brain, liver, bone and lung.
- Melanoma accounts for 2% of all skin cancer, BCC 80%, SCC 18%
- Melanoma accounts for 75% of all skin cancer deaths
- Melanoma is the 3rd most common cancer in men (after prostate and bowel cancer)
- Melanoma is the 3rd most common cancer in women (after breast and bowel cancer)
- Melanoma comprises around 10% of all cancer diagnoses in men and women
- Melanoma is the most common skin cancer in young people (15-39 year olds)
- New Zealand and Australia respectively have the highest incidence of melanoma world wide
- Over 13000 Australians are expected to be diagnosed with melanoma each year
- Melanoma is very rare in children, less than 1%
- 1 in 14 men and 1 in 24 women will be diagnosed with melanoma during their lifetime
- If detected early, melanoma is curable.
- 90% of those who have their primary melanoma removed will survive 5 years.
Several risk factors will increase an individual’s risk of developing the most common melanoma (superficial spreading melanoma)
- Increasing age (90% of melanomas occur after 45)
- Fair skin
- previous diagnosis of melanoma
- previous diagnosis of Non Melanoma Skin Cancer (BCC, SCC)
- high numbers of moles
- greater than 5 atypical naevi (dysplastic or large)
- frequent sunburn
- 5 or more blistering episodes of sunburn
- strong family history with 2 or more first degree relatives having had melanoma
- regular use of tanning beds
Melanoma most commonly presents on the skin but can also occur in other areas such as mucous membranes, mouth, lips, genitals, eye and brain. In men, most commonly melanomas present on the back (40% of all melanomas in men) and in women on the legs (35%). It can present in skin even in non sun exposed areas such as the sole of the foot.
Melanoma can arise from a pre existing mole that has transformed or it may arise in normal skin where there is no previous mole. It will most commonly look like an unusual mole and may have a multitude of colours including dark brown, tan, black, red, blue and light grey. Amelanotic melanomas will have an absence of colour and look clear. Some melanomas especially if regressing will have skin colour, white or scarring.
Melanomas will tend to be flat in the early stages during the horizontal growth phase but take on thickened or nodular appearance once the vertical growth phase commences. Melanomas may ulcerate or bleed and some may itch or become tender.
Melanomas will tend to have the following features:
- changing size
- asymmetrical shape or irregular jagged border
- asymmetrical colouring or pigment pattern
- if 6 mm or more it will have a higher chance of being a melanoma
- ulceration or a sore that won’t heal
- itchy or painful
These features can be summarised by the ABCDE’s of melanoma
B: border irregularity
C: colour variation
D: diameter over 6 mm
E: evolving size or shape
The majority of melanomas are detected by one’s self or their family member. A suspicious lesion such as new mole looking lesion or an existing mole that has made a change should prompt a visit to a GP, Skin Cancer Physician or Dermatologist. In other cases, a melanoma may be clinically suspected during a skin examination. Often the doctor will examine the lesion with a dermatoscope which can give further clues as to the diagnosis. Through the science of dermatoscopy, algorithms have been developed to help diagnose melanoma more reliably but also to minimise unnecessary biopsy of benign lesions.
Once a lesion is suspected to be a possible melanoma, a biopsy will be organised by the doctor. A biopsy involves injection of a local anaesthetic before either a full excision of the lesion or a deep shave to remove the whole lesion. The specimen is then sent to a pathologist who will slice the lesion into small slices for examination under the microscope. A pathological diagnosis is then made which will help in deciding the treatment option and long term prognosis.
The Pathologist will report on the following findings:
- The macroscopic appearance of the lesion to the naked eye
- Diagnosis, whether primary or secondary melanoma or another benign lesion
- Classification or type of melanoma (i.e. superficial spreading, nodular, amelanotic etc)
- Breslow thickness for invasive melanoma
- Clark level of invasion
- Surgical margin (normal tissue around the lesion)
- Mitotic rate – a measure of how fast the cells are proliferating
- Pre existence of a previous mole
The 2 most useful findings used for future diagnosis, staging and treatment are the Breslow thickness and Clark Level.
This is the measurement of the vertical height of the melanoma. The thicker the Breslow Thickness, the higher the chance of future metastasis and the worse the long term prognosis. A Breslow Thickness less than 1 mm is associated with a good long term prognosis (in general).
This is a measure of the anatomical level of growth/invasion of the melanoma.
Level 1: In situ melanoma, contained within the epidermis
Level 2: Melanoma has invaded papillary dermis
Level 3: Melanoma has filled papillary dermis
Level 4: Melanoma has invaded reticular dermis
Level 5: Melanoma has invaded subcutaneous tissue
The further the level of invasion, the worse the prognosis.