Disease classification systems, including those for cancer, are usually developed by leading experts based on prototypical cases and then adopted in routine diagnostic evaluation in all sections and at all levels of the healthcare services. Without validation of diagnostic criteria in this context, these classification systems, i.e. diagnoses, may turn out to be inappropriate with suboptimal validity and reliability (4). The World Health Organization published its most recent classification system of skin tumours in 2018 (12). In Norway, pathologists have largely continued to use poorly defined terms such as irregular nevus and nevus with severe atypia. These two terms correspond to what would be referred to internationally as dysplastic nevus with moderate atypia and dysplastic nevus with severe atypia, respectively. It is recommended that such lesions be excised in toto, mainly to ensure histopathological visualisation of the entire lesion (20).
Leading pathologists have recommended adopting a simpler classification system, Melanocytic Pathology Assessment Tool and Hierarchy for Diagnosis (MPATH-Dx), for the diagnostic evaluation of melanocytic skin lesions (21). This system uses only five diagnostic categories, roughly equivalent to the six used in our study. This type of simplification would enable improved communication between pathologists and clinicians, but does not solve the problem of possible overdiagnosis. The World Health Organization has introduced several new categories for melanocytic proliferations (12), such as melanocytoma, superficial atypical melanocytic proliferations of unknown significance (SAMPUS), melanocytic tumours of uncertain malignant potential (MELTUMP) and many others (22). There is much to suggest that these types of lesions should be considered as risk factors for melanoma rather than precursors to melanoma (23). However, it is difficult to study the clinical course of untreated dysplastic nevus and melanoma in situ because these diagnoses can only be confirmed by removal and histological examination of the lesion. Following radical excision of the lesion, the risk of further growth and metastasis is eliminated. The identification of cases in which excision of pigmented skin lesions is indicated can be improved by using dermatoscopy and confocal microscopy (24, 25). In the future, the use of artificial intelligence and machine learning may help simplify and improve the diagnostic evaluation of skin lesions suspected to be cancer (26).
Knowledge about the pathogenesis of melanoma and other melanocytic skin lesions is growing rapidly (27). New molecular biomarkers may potentially lead to more reliable and more reproducible diagnostic criteria. There will be an increased need for more expertise among pathologists in routine diagnostic evaluations. Our study and other studies indicate that difficult cases of melanocytic skin lesions should be examined by at least two pathologists (4). It is our opinion that consideration should be given to some degree of centralisation of dermatopathological activities in Norway, for example in the form of regional competence centres. Digitalisation of histopathological slides will give pathologists better opportunities to consult with colleagues at other laboratories. In several countries, dermatopathology is a separate subspecialty or a separate area of qualification for pathologists.
Openness about the fact that the diagnostic evaluation of pigmented skin lesions can be laden with uncertainty is just as important as increased expertise and knowledge, validated diagnostic criteria and new terminology (28). Medicine may have oversold the ability and opportunity of doctors to make definite diagnoses with a likely course and outcome for each patient. The task of conveying clinical judgement and uncertainty in the diagnostic evaluation of pigmented skin lesions can be difficult and requires professionalism and communication skills on the part of the doctor (2).
This study must be regarded as a pilot study. In our opinion, a larger study should be undertaken to investigate whether diagnostic drift may help explain the sharp increase in the incidence of cutaneous melanoma in Norway in recent decades (8).