CEACAM5 and neoplasm: Thus, CEA-positive tumor cells could bond to brain vasculature, favoring CNS metastasis development, similar to leukocyte transendothelial arrest and migration through blood-brain barrier mediated by integrin-Ig adhesion interactions [37]; in addition, this could be explained by paraprotein-secreting cells, such as mononuclear cells with Ig-kappa and lambda light chains, which preferentially pass from peripheral blood to CSF [38].