The purpose of this study was to assess the usefulness of HER2 level measurement of US-FNA specimens (FNA-HER2) from ALNs in the determination of lymph node metastasis or characterization of primary breast cancer, and to compare the HER2 status of metastatic ALNs based on FNA-HER2 with that of primary breast cancer tissue. The gene discussed is ERBB2; the disease is breast cancer.