About 70% of melanomas are superficial spreading melanoma (SSM). They develop out of a pre existing nevus , which are the brown spots that every person has a few of. A nevus is a potential melanoma precursor lesion. There might be an incubation period of 1 to 5 years where the nevus is slowly growing, changing color, getting somewhat more raised and perhaps getting surrounded by a red line.
All those are warning signs that this nevus is dysplastic, moving towards malignant transformation. This nevus needs to be surgically removed to avoid trouble down the road. If it is not removed, the surface may become glossy and become more irregular.
Progression of dysplastic nevus to early melanoma
Here is an image of a superficially spreading melanoma where there are areas of regression of the tumor (lighter color), but the remainder of it is spreading (dark color).
There may be some notching or indentation at the perimeter of the lesion and the color may become deeper pigmented, at some areas even black looking. A small patch of the lesion may even turn amelanotic (amelanotic melanoma, looks skin colored). Women tend to have more of this type of melanoma. It tends to be less aggressive and has a better prognosis.
References
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2. The Merck Manual, 7th edition, by M. H. Beers et al., Whitehouse Station, N.J., 1999. Chapter 126, p. 843-845.
3. Cancer: Principles&Practice of Oncology. 5th edition, volume 2. Edited by Vincent T. DeVita, Jr. et al. Lippincott-Raven Publ., Philadelphia,PA, 1997. Chapter on Cutaneous melanoma.
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5. SA Rosenberg Nature 2001 May 17;411(6835):380-384.
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