Novel genetic alteration in congenital melanocytic nevus: MAP2K1 germline mutation with BRAF somatic mutation

Congenital melanocytic nevus (CMN) represent a benign proliferative skin disease in the epidermis and dermis. CMN are historically known to be associated with activating NRAS or BRAF mutations. Melanoma frequently harbors the BRAF p.Val600Glu mutation, which is also commonly found in benign nevi. A recent study reported mutation of MAP2K1, a downstream effector of the RAS-RAF-MEK pathway, in melanoma with an overall frequency of 8%. Later, in 2019, Jansen P detected one activating MAP2K1 mutation in acral nevi. However, it is unknown whether MAP2K1 mutations are common in CMN, and how MAP2K1 contributes to the pathogenesis of CMN remains to be determined. In this study, we report one patient clinically and histologically diagnosed with CMN, with the MAP2K1 germline mutation and a BRAF p.Val600Glu somatic hit in the lesion. To the best of our knowledge, this is the first report of the coexistence of mutated BRAF and MAP2K1 in CMN, which may suggest that MAP2K1 mutations contribute to the occurrence and development of nevus expanding our knowledge of the genetics of CMN.