International pathologists congruence survey on quantitation of malignant melanoma

A congruence survey of pathologists in Brisbane, Adelaide, Oslo and Paris on classifying and grading histological features such as dermal invasion, cross-sectional profile, mitotic activity and lymphocytic infiltrate was done on 147 cutaneous melanomas. The overall agreement was about 70%, about one pathologist in three or four disagreeing on each feature. Taking into acount also the considerable number of slides in which agreement was less, the results are considered unsatisfactory. Agreement was highest in cross-sectional profile and least in level of invasion. It is evident that the gradings are subjective and indicate the need for detailed histological description in making the criteria and the necessity of collaboration between pathologists to study slides and clarify problems. Experience is important and the slides must be of high technical excellence. Comparisons of results between different pathologists on the histological quantitations of malignant melanoma should take note of the degree of congruence achievable.