Photos - click on tab labeled Superficial spreading melanoma
Superficial spreading melanoma evolves fifty percent of the time from a dysplastic nevus. Melanoma can also arise directly as melanoma in the other 50% of cases. A 1 mm black dot, often with a fine scale on top, can be in-situ or minimally invasive melanoma. That said, fifty percent of superficial spreading melanoma have an identifiable nevus in them. That nevus is the presumed precursor lesion.
Superficial spreading melanoma can, in many cases, be recognised as an extension of the abnormalities noted in dysplastic nevi. Its features include Asymmetry, irregularity of Border, Colour variation, and large Diameter. These ABCD rules can be useful, but many melanomas are not identified using them. For instance, the D of ABCD includes a lesion diameter greater than 6 mm in diameter. Thanks to an educated physician and general public, melanomas in Australia are diagnosed smaller than 6 mm 60 percent of the time. Thus size alone is not a useful predictor, unless the lesion is large. Similarly, edge and colour variation are common in very tiny new nevi that are not dysplastic. As nevi evolve beyond 2 to 4 mm, the variation becomes less and less in the normal nevus. Conversely, the irregularity of edge and colour can be accentuated in the dysplastic nevus evolving into a melanoma.
Thus, while the ABCD rule is useful as a way of thinking about morphology, strict adherence to it may result in the missing of some melanomas.
Another rule that is sometimes useful is the "ugly duckling rule". If all of the patient's nevi are a pale to mid brown colour and one of them is very dark, that one is suspect. Similarly, if all the patient's nevi are very dark and one is showing evidence of pale brown, that one is suspect. In other words one looks for the nevus that does not fit in the general pattern. That general impression approach can be very useful.
Yet another rule is to rely on the experience that you the practitioner have gained over many years. If the average individual has 50 nevi, you will have seen, assuming that at least the shirt is removed from the patient, many hundreds of nevi a day for your practice life. When you see something that does not fit in to the pattern that you have been seeing for years, that lesion warrants a closer look, and possibly a biopsy. This later rule can be called the "experience" rule and is quite possibly the most useful rule of all.