Melanoma has has two main categories, in situ and invasive.
In situ melanoma.
These are melanomas that are confined to the outer (epidermis) layer of the skin. This is the least dangerous type of melanoma. These cancers rarely spread if removed early with a 5 mm margin of normal skin. Some of these in situ melanomas are called “lentigo maligna” or “Hutchinson’s melanotic freckle”. They most frequently occur on the head and ncek of older people.
Invasive melanoma.
These are melanomas that are not confined only to the epidermis. They have now grown into the next skin layer, the dermis. The wide excision of these melanomas generally includes a minimum 10 mm margin of normal skin around the excisional biopsy site. The more the melanoma has grown deep into dermis, the greater the risk that it may have spread to distant sites. There are several types on invasive melanoma detailed below:
Superficial spreading melanoma. This is the commonest type of melanoma. These are often irregular in shape and variable in colour. They often have many colours within the tumour. If caught early and excised with a healthy margin of normal skin, these melanomas are frequently cured.
Lentigo maligna melanoma. These are often very dark in colour and have been growing slowly for some time. They are most common on the head and neck of older people.
Nodular melanoma. These can look very different. They can be round and pink. For this reason, people often do not suspect the skin lesion is melanoma. These can be very dangerous melanomas. Often the Breslow thickness is quite large at the time of diagnosis. These melanomas comprise around 18% of all melanomas but account for over 50% of deaths from melanoma.
Acral melanoma. These are very different. Acral melanomas grow on the hands of feet. Specifically, they grow in the base of the nails or on the “fingerprint” type skin of the palm, sole, fingers or toes.
There are other rarer types of melanoma such as spindle cell melanoma, desmoplastic melanoma, dermal melanoma and the occasional melanoma that does not start on the skin.
From time to time, the first we know of a patient’s melanoma is that it has spread. A person might develop symptoms from secondaries in the brain or liver, etc,. These might be found to be from a melanoma, even though no skin lesion has ever been found.