Melanoma has a variety of clinical presentations with different histological features.
This is important to recognise it:
- The most common form is the superficial spreading melanoma (SSM) which in its early stages will be a flat lesion often originating from a flat junctional naevus, often has a horizontal growth phase at first followed by a vertical growth phase when atypical melanocytes spread into the dermis. Once SSM progresses it can develop raised areas which often imply a poorer prognosis.
- In nodular melanoma, the lesion may present as a very small black nodule growing over weeks or months.These lesions have a vertical growth phase from the onset and are usually more aggressive.
- Lentigo maligna are melanoma seen in older subjects on chronically sun- exposed sites, usually the face. They often originate from a longstanding pre- existing lentigo which slowly becomes darker and larger. There are two forms of lentigo maligna:
- Those without invasion in the dermis which have an excellent prognosis.
- Those with invasion of atypical melanocytes spreading in the dermis.
These lesions are regarded as more dangerous and require more aggressive treatment.
Melanoma can also appear on the palms and soles or under the nail and on those sites may present as a vascular non-pigmented lesion which may cause diagnostic problems. These lesions are often diagnosed very late and have a poorer prognosis.
Melanoma is extremely rare in non- Caucasians and, when it does occur, affects the non- pigmented palms and soles but not the pigmented part of the skin.
Women are more likely to develop melanoma on the legs while men are more likely to have melanoma on the trunk. It is extremely rare in children as melanoma risk increases with age.
However, relative to other cancers, melanoma is the most common cancer between the ages of 20 and 35 in Caucasians but it should be remembered that the incidence of melanoma is still very low in that age group.4 Common cancers such as breast, lung and colon, for example, are around ten times more common than melanoma.
