What criteria reliably distinguish melanoma from benign melanocytic lesions?

The differential diagnosis of melanocytic lesions is fraught with difficult y and a common source of litigation either if a lesion misreported as 'beni gn' recurs locally or re-presents with nodal metastases or if an atypical n aevus is called 'malignant' leading to a cosmetically unsatisfactory wider resection, unwarranted anxiety about prognosis and adverse life insurance p rospects. Several authors have claimed that there are valid morphological c riteria which, alone or in combination, enable reliable distinction between benign and malignant melanocytic lesions. Others question these criteria a nd, doubting the extent to which unequivocal diagnoses can be rendered in a ll cases, believe that the diagnosis is purely subjective and that most dia gnostic errors are non-negligent. To address these issues, expert opinions were commissioned from three sets of authors. Okun, Edelstein & Kasznica emphasize that a significant minority of melanoc ytic lesions are so borderline morphologically that diagnostic uncertainty is allowable and that such uncertainty can be handled responsibly Kirkham, in favouring the methodical use of criteria, concedes that they are 'largel y opinion-based rather than evidence-based, but do go beyond mere subjectiv e pattern analysis'. In agreement with Okun and his colleagues, Slater emph asises that no single feature is reliable by itself and that all aspects, i ncluding clinical details, should be interpreted together; he has no hesita tion in reporting the diagnosis as 'uncertain' in doubtful cases. In the absence of a specific, marker pathognomonic of melanocytic malignanc y, the diagnosis will continue to rely on the judicious application of morp hological criteria with a small proportion of elusive cases in which diagno stic uncertainty should not be concealed.