Inclusion Criteria:  Adult patient at the time of diagnosis (> = 18 years). histopathological diagnosis of "ambiguous melanocytic proliferation" or "atypical melanocytic proliferation" made between January 2016 and December 2020. Histological slides archived in the "CRB" biobank available Formalin-fixed paraffin-embedded tissue block archived in the "CRB" biobank available Informed patient  Exclusion Criteria:  Patient who has expressed opposition to participating in the study.