POU2F3 and small cell lung carcinoma: In recent years, researchers have classified SCLC into four subtypes: SCLC-A, SCLC-N, SCLC-Y, and a distinct subtype of SCLC with lower expression of all three transcription factors, based on the differential expression of key transcriptional regulatory factors such as achaete-scute homologue 1 (ASCL1), neurogenic differentiation factor 1 (NeuroD1) and POU class 2 homeobox 3 (POU2F3) (28).