KRAS and adenocarcinoma: Several recent molecular studies have identified two major types of pulmonary LCNEC—one with genomic features of SCLC, characterized by RB1 and TP53 alterations, and the other with genomic features of NSCLC, characterized primarily by alterations typical of smoking-associated adenocarcinoma (STK11, KEAP1, KRAS) and the absence of RB1 alterations, with a minority of cases exhibiting mixed or indeterminate features22,94,95.