POU2F3 and neoplasm: In the current study, using TMAs and specimen slides from a relatively large cohort (N = 192) of primary resected SCLC, we assessed the tumor‐derived protein expressions of ASCL1, NEUROD1, POU2F3, YAP1 as well as VIM, a mesenchymal marker which may be a potential assay to define SCLC‐I.