Then we generated Smurf1-WT or Smurf1-T223A expressing breast cancer cells by reintroducing Smurf1-WT or Smurf1-T223A into Smurf1 knockdown cells, and injected the cells into the mammary fat pad of female BALB/c mice to examine the primary tumor growth and lung metastasis. The gene discussed is SMURF1; the disease is breast cancer.