SCLC-like LCNEC is characterized by some molecular alterations typical of conventional SCLC, such as retinoblastoma 1 (RB1) and TP53 inactivation, MYCL1 amplification, CREB binding protein (CREBBP), EP300 and KMT2A gene mutations, as well as fibroblast growth factor receptor 1 (FGFR1) amplifications; however, they differ from conventional SCLC in their transcriptomic profile (ASCL1-low/DLL3-low/Notch-high profile in SCLC-like LCNEC versus ASCL1-high/delta-like 3 (DLL3)-high/Notch-low expression profile in conventional SCLC). This evidence concerns the gene CREBBP and large cell neuroendocrine carcinoma.