Novice identification of melanoma: not quite as straightforward as the ABCDs

Abstract

The "ABCD" mnemonic to assist non-experts' diagnosis of melanoma is widely promoted; however, there are good reasons to be sceptical about public education strategies based on analytical, rule-based approaches--such as ABCD (i.e. Asymmetry, Border Irregularity, Colour Uniformity and Diameter). Evidence suggests that accurate diagnosis of skin lesions is achieved predominately through non-analytical pattern recognition (via training examples) and not by rule-based algorithms. If the ABCD are to function as a useful public education tool they must be used reliably by untrained novices, with low inter-observer and intra-diagnosis variation, but with maximal inter-diagnosis differences. The three subjective properties (the ABCs of the ABCD) were investigated experimentally: 33 laypersons scored 40 randomly selected lesions (10 lesions × 4 diagnoses: benign naevi, dysplastic naevi, melanomas, seborrhoeic keratoses) for the three properties on visual analogue scales. The results (n = 3,960) suggest that novices cannot use the ABCs reliably to discern benign from malignant lesions.

Fig. 1

A screen “snapshot” of the purpose-built software used to record the 33 subjects’ assessments of the three ABC properties. The subjects scored each of the three properties on the 10-point visual analogue scales that were displayed to the right of the image, by moving the slider to the desired level.

Fig. 2

A screen “snapshot” taken from the SkinCancerNet website (35), demonstrating the caricatured images that we used as the anchor points for the visual analogue scales in our software. The pictures on the right were used as they demonstrate the analytical criteria of the ABC, but without facilitating any non-analytical pattern recognition that could have developed if the “real-life” images had been used.

Fig. 3

The full results of all 3,960 comparisons undertaken are split according the ABC properties assessed into three plots (a: asymmetry; b: border irregularity; c: colour uniformity). Each horizontal bar represents an individual’s score. The 40 lesions assessed are displayed in columns across the x-axis, grouped by their diagnostic classes (green = benign naevi, orange = dysplastic naevi, red = melanomas, blue = seborrhoeic keratoses). The median score for each diagnostic class is demonstrated by the large horizontal black bar.

Fig. 4

An enlarged display of the highlighted section of Fig. 3b, showing all the border irregularity visual analogue scale (VAS) scores for the 10 melanoma lesions. The lesions with the highest variation (lesion 3, interquartile range (IQR)=4.86) and lowest variation (lesion 7, IQR=1.93) are further highlighted, in blue and cyan, respectively, to demonstrate the large spread of scores attributed to lesions within the same diagnostic class. For lesion 3 it can be seen that the range of scores attributed by the 33 subjects was 0.7–10, with a median of 6.6, and for lesion 7 the range was 0–5.5, with a median of 1.3.