CCNE2 and small cell lung carcinoma: By intersecting differentially expressed exLRs related to PFS and OS, the chemo-sensitive vs. chemo-refractory group and specifics in the SCLC group compared to healthy controls, ten exLR markers (EPCAM, CCNE2, CDC6, KRT8, LAMB1, CALB2, STMN1, UCHL1, HOXB7 and CDCA7, as shown in Table 3) were selected and used to construct a SCLC classifier.