Medicine Dermatology · Clinical · High Yield

ABCDE Mnemonic — Melanoma

The ABCDE criteria provide a systematic visual checklist for identifying features of malignant melanoma in pigmented skin lesions. They are taught to both clinicians and the public as the primary screening tool.

✦ The Mnemonic

"Asymmetry, Border, Colour, Diameter, Evolution"

Five visual warning features of malignant melanoma

A Asymmetry One half of the lesion does not mirror the other — asymmetrical shape

B Border Irregular, ragged, notched, or blurred borders — not a smooth clean edge

C Colour Variation in colour within the lesion — different shades of brown, black, red, white, or blue

D Diameter Diameter greater than 6 mm (size of a pencil eraser) — though melanomas can be smaller

E Evolution Any change in size, shape, colour, or a new symptom (bleeding, itching, crusting)

📚 Clinical Breakdown

The ABCDE criteria were developed in 1985 by Friedman and colleagues and remain the most widely used clinical screening tool for melanoma. Evolution (E) was added later and is arguably the most important feature — any lesion that is changing warrants urgent review regardless of other criteria. A patient's report of change should always be taken seriously.

Dermoscopy significantly improves diagnostic accuracy beyond the naked-eye ABCDE assessment — sensitivity increases from ~70% to ~90% with dermoscopy in trained hands. Key dermoscopic features of melanoma include atypical pigment network, irregular streaks, regression structures, and blue-white veil.

Melanoma is staged by Breslow thickness (depth of invasion in mm) — the single most important prognostic factor. T1: ≤1.0 mm; T2: 1.01–2.0 mm; T3: 2.01–4.0 mm; T4: >4.0 mm. Sentinel lymph node biopsy is offered for T1b and above. Five-year survival: T1a ~98%; T4b with nodal disease ~40–50%.

Most important feature Evolution — any change in a lesion

Diameter threshold >6 mm — but early melanomas can be smaller

Breslow thickness Key prognostic factor — measured in mm

Urgent referral 2-week wait referral for any suspicious pigmented lesion

⭐ Clinical Pearl

The 'ugly duckling' sign: a lesion that looks different from all the other moles on a patient's skin — the outlier — is more suspicious than absolute ABCDE criteria alone. Patients with many dysplastic naevi may have lesions that score poorly on ABCDE but are benign. The lesion that stands out from the patient's own baseline pattern is the one to watch.

⚠ Exam Trap

Amelanotic melanoma is a trap — it lacks pigment and can present as a pink or flesh-coloured nodule that does not trigger the ABCDE checklist. It accounts for ~5% of melanomas and is frequently diagnosed late. Any new pink/red growing nodule should be treated with suspicion.

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