Melanoma is a malignant skin cancer that should be treated very seriously. Melanoma develops due to an uncontrolled growth of pigment cells, called melanocytes.
Typical melanocytes are located in the basal layer of the epidermis (this is the lower section of the outer layer of the skin). A commonly known protein is melanin (the protein that allows our skin to tan from the sun). Melanocytes are responsible for producing melanin; it's function is to protect the skin by absorbing ultraviolet (UV) radiation.
No matter your skin tone (fair or dark), we all have an equal number of melanocytes. The difference in skin tones, is the difference between how much melanin is produced by these melanocytes. The more melanin that is produced, the less likely your skin will be damaged by UV radiation. Therefore the fairer you are, the more at risk you are.
Melanocytes can form non-cancerous growths. These are known as moles (or benign melanocytic naevi) and freckles (ephelides and lentigines). The cancerous growth of melanocytes however, results in melanoma.
Melanoma is most common in adults, but in rare cases children have been diagnosed with malignant melanoma. It can be a potentially fatal mistake to assume you won't get melanoma. Australia has the highest incidence of melanoma in the WORLD, so it is vital to have a regular (annual) full skin examination to ensure any moles or freckles are benign.
Predominantly, melanoma is caused by the sun, however genes can play a part too. Scientific studies of melanoma in this field, called genomics, is on the rise, so we can better understand the condition and how to treat it. Some families may have familial melanoma, which is due to mutations in genes that have been passed down from parent to child. Melanoma caused by inherited genes is suspected if two or more first-degree relatives (parent, brother, sister or child) are diagnosed with melanoma.
There are also several specific mutations that have been evident in different families with melanoma. Nearly 40% of individuals have mutations within the CDKN2A gene. Individuals affected within these families with this abnormality may inherit the trait of many large moles.
In approximately 75% of cases, melanomas will surface within a mole or freckle. However it can also appear in otherwise normal appearing skin. If it surfaces within a mole or freckle, it will start to change in appearance. Warning signs include these precursor lesions:
1) Benign melanocytic naevus (normal mole) 2) Atypical or dysplastic naevus (funny-looking mole) 3) Atypical lentiginous junctional naevus (freckle in heavily sun damaged skin) 4) Congenital melanocytic naevus (brown birthmark)
It's common for melanomas to present any where on the body. It's not even exclusive to sun-exposed body parts. Common areas are the back and legs. Very rarely, melanoma can grow on mucous membranes such as the lips or genitals. Even more rarely, it can be diagnosed on the eye, brain and mouth.
As mentioned previously, the first sign of a melanoma is usually an unusual looking freckle or mole. It's possible for a melanoma to be detected at an early stage when it is only a few millimetres in diameter, but in many cases they may grow to several centimetres in diameter before they are diagnosed. This is due to a lack of awareness about melanoma, and the importance of regular skin checks, particularly if you are fair and have a large number of moles and/or freckles.
A melanoma can have different hues; tan, dark brown, black, blue, red and, occasionally, light grey. Melanomas that are lacking pigment are called amelanotic melanoma. There may be areas of regression that are the colour of normal skin, or white and scarred.
If you have a pigmented lesion (mole or freckle), it should be seen by an experienced doctor as soon as possible. Not all such lesions are malignant, but there is an increased chance, so it's better to be safe.
We identify melanomas according to their appearance and behaviour. Below are the different categories of melanoma, and the different types of melanoma within these categories.
1) Those that start off as flat patches (i.e. have a horizontal growth phase) include:
- Superficial spreading melanoma (SSM)
- Lentigo maligna melanoma (sun damaged skin of face, scalp and neck), and lentiginous melanoma (on trunk and proximal limbs)
- Acral lentiginous melanoma (on soles of feet, palms of hands or under the nails – the subungual melanoma)
All of the above are superficial forms of melanoma that tend to grow slowly. However at any point, they may begin to thicken up or develop a nodule (i.e. progress to a vertical growth phase).
2) Melanomas that rapidly progress to deeper tissues:
- Nodular melanoma (presenting as a rapidly enlarging lump)
- Mucosal melanoma (arising on lips, eyelids, vulva, penis, anus)
- Neurotropic and desmoplastic melanoma (this is a fibrous tumour with a tendency to grow down nerves)
- Ocular melanoma
Within this category, it's common to see combinations of these develop e.g. nodular melanoma arising within a superficial spreading melanoma or desmoplastic melanoma arising within a lentigo maligna.
3) Melanoma can also be categorised according to its relationship with sun exposure, age and number of melanocytic naevi.
4) Childhood melanomas (below 10 years of age):
- Are extremely rare
- Are not associated with excessive sun exposure
- More often amelanotic (flesh coloured, pink or red), nodular, bleeding and ulcerated compared to melanoma in adults
- May arise within giant congenital melanocytic naevi > 40 cm diameter
5) Early-onset melanomas:
- More common in women
- Most common clinical subtype is superficial spreading
- Associated with many melanocytic naevi
- Tend to be seen on lower extremity
- Tends to have BRAFV600E genetic mutation
- Associated with intermittent sun exposure
6) Late-onset melanomas:
- More common in men
- Most common clinical subtype is lentigo maligna
- Often occur on head and neck
- Associated with accumulated, lifelong sun exposure