YAP1 and small cell lung carcinoma: Based on analytical results from human primary SCLC tissues, patient-derived xenografts, mouse genetic models (GEMMs) and SCLC cell lines, Rudin et al. [19] summarized previous classification methods and identified differences in the expression of the main transcription factors: ASCL1, NEUROD1, YAP1 and POU2F3, SCLC into four molecular subtypes as follows: SCLC-A, SCLC-N, SCLC-Y and SCLC-P [18,19].