POU3F2 and small cell lung carcinoma: Based on the expression of transcription factors such as achaete-scute homolog 1 (ASCL1; also known as ASH-1), neurogenic differentiation factor 1 (NEUROD1), and POU class 2 homeobox 3 (POU2F3), SCLC is now subdivided into four categories: SCLC-A (high ASCL1 expression), SCLC-N (high NEUROD1 expression), SCLC-P (high POU2F3 expression), and SCLC-I (low expression of the three transcription factors but elevated levels of inflammatory markers) (8).