At what diameter in millimeters is a lesion considered suspicious for melanoma?

Suspicious Skin Lesions for Melanoma: Diameter Criteria

A lesion with a diameter greater than 6 mm is considered suspicious for melanoma according to the established ABCDE rule for melanoma screening. 1

Understanding the Diameter Criterion

The ABCDE rule is a well-established guideline for identifying suspicious skin lesions that may represent melanoma:

• A: Asymmetry
• B: Border irregularities
• C: Color heterogeneity
• D: Diameter >6 mm
• E: Evolution/Elevation/size changes

The 6 mm diameter threshold has been consistently maintained in clinical guidelines as an important parameter for melanoma suspicion 1. This criterion helps clinicians determine which lesions warrant further evaluation, including potential biopsy.

Evidence Supporting the 6 mm Criterion

Research supports the continued use of the 6 mm diameter criterion:

• A 2008 study found that lesions larger than 6 mm had a significantly higher likelihood of being melanoma (5.1% for invasive melanoma) compared to lesions 6 mm or smaller (1.5%) 2
• A 2015 study demonstrated that lesions larger than 6 mm had a higher positive predictive value of 11.5% compared to 2.6% for smaller lesions 3

Important Caveats and Exceptions

While the 6 mm criterion is valuable, clinicians should be aware of important exceptions:

• Small melanomas (<6 mm) do exist and can have similar histologic features, DNA abnormalities, and malignant potential as larger lesions 4
• More recent guidelines acknowledge that many primary melanomas may have a diameter of <5 mm 1
• The diameter criterion should never be used in isolation but always in combination with the other ABCDE criteria 2

Clinical Approach to Suspicious Lesions

When evaluating a lesion for melanoma:

1. Apply the complete ABCDE criteria, not just diameter

2. Consider additional concerning features:

   • Recent evolution in color, elevation, or size
   • Ulceration
   • Symptoms (itching, bleeding, tenderness)
   • The "ugly duckling sign" (lesion looks different from other moles)

3. Use dermoscopy when available to enhance diagnostic accuracy 1

4. For suspicious lesions, perform a full thickness excisional biopsy with a 2 mm margin 1, 5

Conclusion

While the >6 mm diameter criterion remains a useful parameter for identifying suspicious lesions, it should be used as part of the complete ABCDE assessment. Clinicians should maintain vigilance for smaller melanomas, especially when other concerning features are present.