Histopathology diagnoses of thin melanoma compared to dysplastic naevi inconsistent

February 11, 2019


Background: Dysplastic naevi (DN) and thin melanomas may be difficult to distinguish histologically.

Aims: Our aim was to review the inter-rater variability between anatomical pathologists for diagnosing thin melanoma compared to DN, and examine the potential reasons for discordance.

Methods: A consecutive series of DN and thin melanomas (Clark I-III) was retrieved using a database search from the Anatomical Pathology department, St Vincent's Hospital, Sydney between April 2017 and October 2017. One anatomical pathologist and one registrar rated all slides for either melanoma or naevus, blinded to the original diagnosis. The gender, age, type of specimen, site, presence of melanoma with co-existent naevi, melanoma subtype, Breslow thickness, and a history of previous surgery were noted from the original pathology reports.

Results: A total of 66 cases were retrieved, reported by 7 pathologists, comprising 40 melanomas and 26 DN (according to the original histopathology diagnosis). There were 13 punch biopsies, 47 excisions, 3 shave biopsies, and 3 incisional/sliver biopsies. There were 22 melanoma in situ, and 18 invasive melanomas (average Breslow 0.54 mm; range 0.2–1 mm).

The original diagnosis was concordant for both the blinded pathologist and registrar for 25/40 melanomas, and 16/26 DN. The original diagnosis was concordant with the reviewing pathologist for 28/40 melanomas, and 19/26 DN. There were 5 cases that both the reviewing pathologist and registrar called a naevus, with the original diagnosis a melanoma. Of these 5 cases, 3 were associated with a naevus, and four were superficial spreading type melanoma. There were 2 cases that the reviewing pathologist and registrar called a melanoma, with the original diagnosis a DN.

Conclusions: Inter-observer concordant rate appears low. It is likely to be due to the difficulty of this area and the experience of interpreters. Careful examination and intradepartmental second opinion are needed to improve the inter-observer concordance rate.


Maher, N., & Qiu, M. (2019). 19. Examining discordance between histopathology diagnoses of thin melanoma compared to dysplastic naevi. Pathology, 51. doi:10.1016/j.pathol.2018.09.019 


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