Although this was not an in vivo experiment to demonstrate that the changes of the pre-metastatic niche, or Dkk-1 manipulation, increases brain metastasis, these results at least partly indicated the release of Dkk-1 from brain endothelium after uptake of lung cancer cells-derived exosomes contributed to the transendothelial migration of lung cancer cells. The gene discussed is DKK1; the disease is lung cancer.