To improve the treatment outcomes of SCLC, Rudin et al. [8] recently proposed four molecular subtypes of SCLC based on the relative expression of the following key transcription factors: achaete-scute homolog 1 (ASCL1), neurogenic differentiation factor 1 (NEUROD1), yes-associated protein 1 (YAP1), and POU class 2 homeobox 3 (POU2F3), which were SCLC-A (ASCL1-dominant), SCLC-N (NEUROD1-dominant), SCLC-P (POU2F3-dominant), and SCLC-Y (YAP1-dominant). The gene discussed is YAP1; the disease is small cell lung carcinoma.