Merkel cell carcinoma, advanced basal cell carcinoma requiring systemic treatment, and cutaneous adnexal carcinomas are 3 types of rare skin cancers for which much remains unknown in terms of natural behavior, prognosis, treatment and outcomes. CARADERM is a French prospective national cohort enrolling patients with either one of these 3 tumor types, whose objectives are : * to provide epidemiological, clinical and socio-economic characteristics of patients * to identify new clinical or epidemiological prognostic factors for these rare cancers * to evaluate the impact of various treatments on outcomes