CK, cytokeratin; CTCs, circulating tumor cells; DAPI, 4′,6‐diamidino‐2‐phenylindole; EpCAM, epithelial cell adhesion molecule; ES, extensive stage; LS, limited stage; LT‐PCR, ligand‐targeted polymerase chain reaction; OS, overall survival; PFS, progression free survival; RT qPCR, real time quantitative PCR; SCLC, small cell lung cancer; Vim, vimentin. Here, EPCAM is linked to small cell lung carcinoma.