MKI67 and small cell lung carcinoma: The current study also confirmed the phenotypic heterogeneity of CTCs in patients with SCLC as already reported by Hou et al. 13 Indeed, double immunofluorescent staining of CTCs demonstrated that both proliferative (CK+/Ki67+) and non-proliferative (CK+/Ki67−), apoptotic (CK+/M30+) and non-apoptotic (CK+/M30−) as well as CK+/Vim+ and CK+/Vim− CTCs were present at the same time in patients before the initiation of any systemic treatment.