ASCL1 and small cell lung carcinoma: Gathering methylation-based and transcriptomic data from several studies, Rudin and colleagues proposed a classification focused on the differential expression of four key transcription regulators: ASCL1, NeuroD1, yes-associated protein 1 (YAP1), and POU class 2 homeobox 3 (POU2F3). The four proposed categories are SCLC-A, SCLC-N, SCLC-Y, and SCLC-P, with the last letter referring to the transcription regulator whose expression is most strongly associated with each subtype [14].