PECAM1 and metastatic malignant neoplasm in the lymph nodes: For better evaluation of LVI, primary tumors with lymph node metastasis were immunolabeled with platelet endothelial cell adhesion molecule 1 (PECAM1, E4, CD31) monoclonal mouse antibodies (Santa Cruz Biotechnology) at a dilution of 1:750 after pretreatment with citric acid (pH 6) to highlight endothelium of blood or lymph vessels.14 Nuclear pleomorphism was classified as mild = uniform and regular nuclei with minimal anisokaryosis; moderate = increased variability in size (<2-fold difference) and shape; or severe = nuclei varying >2-fold in size.