Quality assessment by expert opinion in melanoma pathology: experience of the Pathology Panel of the Dutch Melanoma Working Party

Abstract

Some cutaneous melanocytic lesions are notoriously difficult to diagnose by histopathology. For that reason, the Pathology Panel of the Dutch Melanoma Working Party was instituted and is regularly approached to provide an expert opinion on problem cases. In order to identify the most common diagnostic problems, 1069 consecutive referral cases of submitted lesions (1992 to 1994 inclusive) were analysed. About 60 per cent of the requests came from small laboratories, with up to three consultant pathologists. Two‐thirds of the lesions reviewed concerned women and nearly 50 per cent of the patients were 30 years of age or younger. In 8 per cent of the cases, the referring pathologists felt unable to make a confident diagnosis; in 14 per cent, melanoma was suspected; and in 12 per cent, a differential diagnosis only had been formulated. The panel felt able to provide an unequivocal diagnosis in 93 per cent of the requests. Of the 158 lesions classified as ‘invasive melanoma’ by the referring pathologists, 22 were considered to be benign by the panel. Conversely, 108 invasive melanomas (panel diagnosis) had originally been considered as benign lesions, dysplastic naevi or melanoma in situ. These high numbers of discordancies reflect the intrinsic difficulty of the differential diagnoses in this selected material submitted to the panel. Diagnostic difficulties were most often encountered with Spitz naevi and dysplastic naevi. Although the rate of overdiagnosis and underdiagnosis is quite high, in the majority of cases the diagnosis of the referring pathologist matched the diagnosis of the panel. This may reflect a proper awareness of difficult melanocytic lesions in pathology practice. The activities of the Pathology Panel of the Dutch Melanoma Working Party contribute to the improvement of the quality of diagnosis in cutaneous melanocytic lesions, as they increase the number of unequivocal diagnoses and reduce the number of incorrect diagnoses. On the basis of the systematic comparison of the diagnosis by the referring pathologist and the panel, postgraduate teaching and quality control can be more focused on specific diagnostic problems. © 1997 John Wiley & Sons, Ltd.

An independent validation of a gene expression signature to differentiate malignant melanoma from benign melanocytic nevi

“…The average discordance between reviewing pathologists was 19.4% in cases receiving an indeterminate score. The overall discordance of 14.1% observed in this study was higher than that for the cohort used in the previous validation study (4.7%) and similar to that reported by other investigations of disagreement in the histopathologic diagnosis of melanocytic lesions 3, 5…”

“…For example, desmoplastic and nevoid melanomas were not specifically excluded from the cohort, but none of the cases classified as either of these 2 particular melanoma subtypes received a triple‐concordant diagnosis by histopathology. The high frequency of discordance among reviewing dermatopathologists in this study was similar to that observed in other assessments of clinical cohorts3, 4, 5, 6, 7 and highlights the need for adjunctive diagnostic tools. An evaluation of the gene signature against clinical outcomes would minimize cohort bias toward straightforward cases, and studies assessing test performance by comparison with clinical outcomes are currently underway.…”

Understanding the progression of melanocytic neoplasia using genomic analysis: from fields to cancer

“…The clearcut difference between the aberration patterns between nevi -no aberrations or presence of an isochromosome 11p -and melanoma -multiple chromosomal aberrations in over 95% of the casessuggests that chromosomal analyses may be of assistance in the classification of lesions that are ambiguous by histopathology. This aspect is of significant clinical relevance, because of the limitations of current techniques to classify reliably tumors that have overlapping histologic features (Farmer et al, 1996;Veenhuizen et al, 1997).…”

Classifying ambiguous melanocytic lesions with FISH and correlation with clinical long-term follow up

“…It is interesting to note that in 8% of the cases the referring pathologist could not provide a confident diagnosis, in 14% the primary 'malignant' diagnosis had to be revised to 'benign' and in 17% the primary 'benign' diagnosis had to be revised to malignant. 7 Recently, genetic approaches have been reported to be of significant help for classifiying melanocytic tumors. Comparative genomic hybridizations (CGHs) demonstrated that specific chromosomal aberrations in melanoma were distinct from chromosomal alterations in nevi.…”