In light of these findings, using tumor expression data and non-negative matrix factorization (NMF), Gay et al. identified four SCLC subgroups defined by the differential expression of transcription factors ASCL1, NEUROD1 and POU2F3 or the low expression of all three transcription factor signatures accompanied by an inflamed gene signature (SCLC-A, N, P and I, respectively) [72]. Here, NEUROD1 is linked to small cell lung carcinoma.