Novel evidence has revealed the existence of CD31 and vimentin double-positive circulating tumour endothelial cells in blood samples from patients with non-small cell lung cancer correlating with poor response to anti-angiogenic therapy and a significantly shortened median progression-free survival, which might be a powerful biomarker for selecting eligible patients and evaluate the anti-angiogenic therapeutic efficacy in clinical practice [35,68]. The gene discussed is PECAM1; the disease is neoplasm.