Since the inhibition of the Nectin-2 function as a cell adhesion molecule may cause adverse effects, we focused on Y-443, which did not inhibit Nectin-2-Nectin-2 or Nectin-2-Nectin-3 interaction (Figure 7), and further evaluated its anti-tumor effect on MDA-MB-231 breast cancer cells in an established mouse lung metastasis model. The gene discussed is NECTIN3; the disease is breast cancer.