melanoma has no rules ?

The ABCDE rules for melanoma have been well publicized, but not all melanomas conform. One type, amelanotic melanoma, for example, has no brown or black. Another kind, nodular melanoma, is often symmetrical, with fairly regular borders and few colours. And invasive melanomas can be smaller than six millimeters — the guideline in the ABCDE rules. The rule for you: Don't dismiss an odd-looking or changing mole because it doesn't resemble the textbook example; show it to a dermatologist.