The average Caucasian has about 15 moles on their body which tend to fade after 35 or 40 years. They develop melanoma more commonly than the general population. The melanoma is often a birthmark that has changed and is more elevated than expected, it itches, it ulcerates, bleeds, and tends to become infected. It is larger than the other birthmarks and it can spread to other parts of the body via the blood stream. These suspicious lesions need to be biopsied, that is have tissue removed for microscopic diagnosis, and in melanoma the biopsy should include complete removal.
Melanomas tend to spread outwards across the skin or downwards into the skin.
The latter types are more malignant. Malignancy can also be gauged by the total thickness of the melanoma. Melanomas occur more in men than in women. They tend to be on the trunk in men and on the legs in women. Those occurring on the upper back, the outside of the arms, the neck, or the skull tend to be more likely to spread than those occurring elsewhere.