Background: The term 'common mole', often used to describe a subset of benign pigmented skin lesions, is traditionally defined on the basis of morpho-chromatic features. In recent years, certain research groups have developed equipment and methods, such as digital dermoscopy analysis, that enable objective evaluation of pigmented skin lesions.
Objective: In this study we use a digital dermoscopy analyser trained for the recognition of pigmented skin lesions to compare the subjective definition of 'common' and the mathematical concept of 'close to the mean of measurements'.
Methods: A subset (100) of digital images of flat pigmented lesions, obtained in daily practice, were classified by trained and non-expert clinicians as common moles (60) or clear-cut melanoma (40), and processed with a DB-Mips analyser. The resulting parameters, validated by a classifier, were used to evaluate Hotelling's T2 multivariate distances from the mean.
Results: 'Common' moles could not be clearly defined in terms of closeness to the means of objectively evaluated parameters. Their diagnosis indudes many other evaluations and clusters of variables.
Conclusion: The clinical semantics of the term 'common' does not conform to any unambiguous mathematical definition.