Fleischer, Feldman, Katz, and Clayton

 
"The patient often reports a new pigmented lesion or mole that has grown or changed in color, size, or shape. The "ugly duckling sign," that is, the appearance of a pigmented lesion that is different from all the other pigmented lesions on the patient, should raise clinical suspicion. For most patients with a melanoma, the lesion is asymptomatic. Pain, if present, usually is associated with a late presentation. Additional information, such as a personal or family history of melanoma, may raise the clinician's level of suspicion, but the key to the diagnosis lies in an examination of the lesion.
 
The acronym ABCD is a useful reminder of some of the clinical features that should raise suspicion of melanoma in a pigmented lesion: asymmetry of the lesion, border irregularity, color variegation or dark black color, and diameter greater than 6 mm (the size of a pencil eraser).
 
The asymmetry of the lesion is the least useful criterion, but the other three criteria seem to have diagnostic significance. Additionally, the new appearance of papules, nodules, or ulceration in a pigmented lesion should prompt a great deal of suspicion. Another worrisome finding is regression in a pigmented lesion, which will appear as a new flat gray or white area in a previously completed pigmented lesion."
 
Fleischer AB Jr, Feldman SR, Katz AS, Clayton BD. 20 Common Problems in Dermatology. New York: McGraw-Hill, 2000:207–9.
 

Brief critique

 
Clichés abound in the preceding paragraphs, among them, the "ugly duckling sign" and the ABCD (which is not an acronym but a mnemonic).
 
The statement by the authors that the "asymmetry of the lesions is the least useful criterion" is just the opposite of reality. Asymmetry is the single most important sign of malignancy because it is the single most dramatic morphological representation of the biologic behavior of the neoplasm. As a rule, benign neoplasms are symmetrical and malignant neoplasms are asymmetrical. Melanoma, being a malignant neoplasm, nearly always is asymmetrical.
 
When the authors wrote that "Additionally, the new appearance of papules, nodules, or ulceration in a pigmented lesion should prompt a great deal of suspicion," they are dealing in woeful understatement; by the time that those features are present, a patient is likely doomed to die eventually of metastasis of melanoma. The emphasis must be on small flat lesions and not on "papules, nodules, and ulceration."