Abstract: Objective: To identify the correlation of proliferative activity and histopathological features associated with mutation status of BRAF(V600E) gene in congenital melanocytic nevi (CMN). Methods: 185 patients with CMN were collected from December 2018 to December 2020 in Department of Dermatology in our hospital. Mutations in all patients were detected by Sanger sequencing. The CMN were divided into mutant group and control group according to whether there was BRAF(V600E) gene mutation, and were strictly matched according to gender, age, nevus size and anatomical site. Histopathological analysis and laser confocal fluorescence microscopy were performed. Results: There were significant differences in Ki67 index, the depth of nevus cell involvement, the number of nevus cell nests and nest size between the mutant group and the control group (Ps<0.05). Compared with the patients of BRAF V600E negative nevi, the patients of BRAF(V600E) positive nevi were usually dominated by nested intraepidermal melanocytes, with larger nests. The number of the nevus cell nests (P=0.009) and the depth of nevus cell (P=0.015) were positively correlated with the Ki67 expression. Conclusion: BRAF(V600E) gene mutations are associated with high proliferative activity and unique histopathological features in congenital melanocytic nevi.

Key words: Ki67, BRAF(V600E), gene, congenital melanocytic nevus