PCA applied to the top 50,000 most variable methylated regions in 33 CDX/PDX models with known molecular subtypes (RNA-seq) revealed accurate unsupervised segregation according to the three categories: NEUROD1 (high NEUROD1 expression with or without coexpression of ASCL1, n = 8), ASCL1 (high ASCL1 expression, n = 24) and double negative (low expression of ASCL1 and NEUROD1, n = 1) (Fig. 5a) confirming methylation differences exist between SCLC subtypes. Here, ASCL1 is linked to small cell lung carcinoma.