BACKGROUND. The mnemonic ABCD, which stands for asymmetry, border irregularity, color variation, and diameter greater than 6 mm alerts physicians to features that suggest melanoma. Although the ABCD criteria are guidelines for diagnosis, clinicians may overlook many melanomas that do not follow the ABCD rule. OBJECTIVE. We examined the sensitivity of the diameter portion of the ABCD rule. METHODS. Retrospective study examining the pathology reports of 383 melanomas. Data were compiled for each melanoma regarding its diameter, depth, body location, patient age, and sex. A 95% confidence interval (p = 0.05) was used to identify the proportion of melanomas less than or equal to 6 mm in diameter. A two-tailed p value approach (p value = 0.05, degrees of freedom = 28) was used when evaluating two independent populations, lesions less than or equal to 6 mm and lesions greater than 6 mm in diameter. RESULTS. A total of 38.21% of melanomas were less than or equal to 6 mm in diameter after processing. Melanomas greater than 6 mm in diameter occurred in significantly older patients and at a greater Breslow's thickness than smaller melanomas. CONCLUSIONS. We demonstrated that a significant proportion of melanomas may be smaller than 6 mm. The ABCD criteria are not absolute; melanomas have many different appearances and start as small lesions.
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