have investigated the transcriptomic relationship between atypical carcinoids (ACs) and LCNECs and have demonstrated that ACs and LCNECs comprise three different molecular diseases of potential clinical relevance: one AC-enriched group (C3) in which MEN1 inactivation plays a major role, one LCNEC-enriched group (C1) whose hallmark is RB1 inactivation, and one group (C2) with intermediate molecular features. This evidence concerns the gene RB1 and large cell neuroendocrine carcinoma.