If all melanomas were diagnosed in situ, no one would die of this disease.1 This is an ideal concept and an unrealistic scenario, but we should at least try to come close to it by detecting melanomas as early as possible. One of the most important prerequisites to accomplish this task is the existence of reliable criteria for the detection of melanomas when they are still small and flat. However, clinical criteria such as the ABCD rule do not work for small melanomas. This becomes evident when considering the letter D of the acronym ABCD, which stands for diameter. A diameter of 6 mm or less is generally regarded as a sign of benignancy, suggesting that melanomas 6 mm or smaller do not exist. In reality, all melanomas start smaller than 6 mm, but at this stage most of them are not asymmetrical, do not exhibit border irregularity, and are not multicolored, as the ABCD rule suggests. The threshold of 6 mm exists primarily because the ABCD rule is not reliable for smaller lesions; it does not, however, indicate a lower size limit of melanoma.2
Kittler H. Early Recognition at Last. Arch Dermatol. 2008;144(4):533–534. doi:10.1001/archderm.144.4.533
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