CD34 was first detected by Civin et al. in 1984 and was subsequently characterized as a hematopoietic progenitor cell marker.33 Recently, increased expression of CD34 and CD31 has been reported on vessel endothelium and endothelial progenitor cells, especially in tumor vascularization.34 Here, monoclonal antibodies against CD34 and CD31 have been used to analyze the microvessel density (MVD) in central and peripheral regions of NSCLC tissue. This evidence concerns the gene PECAM1 and neoplasm.