Section 07 of 12
Safety-net rules
Beyond individual features, certain principles act as safety nets — catching lesions that might otherwise be missed. These are the "do not miss" rules of dermoscopic screening.
The blue-black rule
Any nodular (raised, dome-shaped) lesion with blue-black colouration warrants urgent evaluation.
Nodular melanoma is the most dangerous melanoma subtype because it grows vertically rather than horizontally. It may lack the classic features of superficial spreading melanoma — no atypical network, no asymmetric pigment pattern. Blue-black colour in a nodule indicates deep pigment and is a warning sign that should not be dismissed simply because other "typical" features are absent.
Prediction without pigment
Melanoma can occur without significant pigment. Absence of brown or black does not equal absence of risk.
Amelanotic melanoma is easily missed because it lacks the colour cues we instinctively associate with melanoma. Look for:
- Vascular structures in a nodule without other explanation
- Milky-red areas — pink zones with dotted vessels
- Shiny white structures in a changing lesion
- Clinical history of growth or change in a "colourless" lesion
When a lesion is changing, symptomatic, or simply does not fit any benign pattern — lack of pigment does not provide reassurance. The absence of colour is not the absence of risk.
The ugly duckling sign
A lesion that looks different from a patient's other lesions deserves attention, even if it does not match textbook criteria for concern.
Individuals tend to have a "signature" naevus pattern — their moles generally share a similar appearance. A mole that stands out from this personal pattern — larger, darker, structurally different, or simply odd — may be significant. The ugly duckling sign is one of the simplest and most powerful screening tools available.
The evolution factor
Change over time is significant, regardless of current appearance.
A lesion that is enlarging, darkening, or developing new features is biologically active. Even if it does not look concerning today, the trajectory matters. Patient history of change should lower your threshold for further evaluation, even if the dermoscopic pattern currently seems benign.
A patient presents with a raised, dome-shaped pink lesion that has been growing over the past two months. It has no pigment network, no brown or black colour, but shows some dotted vessels and a milky-red area. Which safety-net rule is most relevant here?