Breslow thickness and histopathologic subtype in a large international population-based study of melanoma To the Editor: As of 2019 National Cancer Institute data show that melanoma is the fifth most common cancer in the United States. 1 There has been a recent push to include the histopathologic subtype of nodular melanoma as an independent prognostic classifier due to the identification of associated aggressive histopathologic characteristics and shorter recurrence-free times. 2,3 We used the population-based, Genes, Environment, and Melanoma (GEM) study, 4 to assess the levels of agreement between community pathologists, those who originally diagnosed the melanoma, and expert study dermatopathologists, who reviewed the lesion for complete histology, histopathologic subtype, and Breslow thickness. The salient components of the GEM study were that it was population-based, multi-country size, and included disease-specific mortality data and rereview of hematoxylin-eosinestained tissues by dermatopathologists. We evaluated how histopathologic subtype misclassification might impact the reported disease-specific mortality.Our study included 1957 individuals with a first primary melanoma diagnosed in the year 2000, at centers of the GEM study in Australia, Canada, Italy, and the United States. The Institutional Review Board approval was obtained, and the subjects signed written consent. Each patient had their hematoxylin-eosinestained slides read initially by a community pathologist, who reported Breslow thickness and histopathologic subtype followed by an independent review by a dermatopathologist, blinded to the community pathologist report. The vital status was obtained at an average of 7.4 years.Within the study population and lethal melanoma cases, descriptive statistics were calculated and the frequency tables that compared the kappa value for the readings of community pathologists and
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