ASCL1 and small cell lung carcinoma: Chen et al. (Chen, et al. 2021) also classified SCLC samples without significant survival difference into four subtypes based on gene expression data—cluster 1 to 4, where cluster 2 and 3 corresponded to SCLC-A and SCLC-N in the subtypes of Gay et al., respectively, and the subtype expressed as the protein of clara cell secretory protein (CCSP) was categorized as cluster 1; The subtype with the lower expression of ASCL1 and NEUROD1, but higher expression of POU2F3 and NOTCH2 was categorized as cluster 4, which was also named “immune subtype” because of its immune-related features.