Melanoma is a cancer of the pigment-producing cell in the skin (the melanocyte).
It may arise from a pre-existing mole, but the majority will arise from where there was no pre-existing mole (i.e. from one of the melanocytes that are scattered evenly in a fine layer across the skin surface).
A new or changing spot is very important. Melanoma typically may look like a mole but it changes over a number of months in size, shape, and colour.
Melanomas are usually not symptomatic. They are usually seen rather than felt. Sometimes, though, there may be sensory changes (usually itching), and if this is persistent then it can be helpful in raising suspicion. As the melanoma invades more deeply, bleeding and crusting can occur, and it becomes more raised.
The most common type of melanoma (superficial spreading melanoma) follows the 'ABCD' rule for clinical assessment:
- Asymmetry. Melanomas are more asymmetric in shape and structure than normal moles. You cannot pass a line through it to create a mirror image.
- Border irregularity. Melanomas have borders that are more irregular than normal moles, which are often more rounded or oval in shape.
- Colour variation. Melanomas often have multiple colours, especially black, whereas normal moles usually only have a few, typically light or dark brown.
- Diameter. Melanomas are usually larger in diameter, often >6mm.
Less commonly, an aggressive type of melanoma (nodular melanoma) can present as a rapidly growing symmetric nodule, fairly uniform in colour, that may be pigmented or sometimes just pink or red.
Melanoma risk increases progressively with an increase in:
- total number of moles e.g. >100
- atypical moles
- previous primary melanomas
- family members with melanoma
- severe sunburns and recreational sun exposure
- non-melanoma skin cancers
- skin types that tend to burn rather than tan
It is important that high-risk patients are checked regularly at the Skin Cancer Clinic, and these patients may also benefit from total body photography.