ERBB2 and metastatic malignant neoplasm in the lymph nodes: First, population-based cancer registration is aimed at monitoring outcomes only, and does not contain detailed clinical information on prognostic factors (hormone receptor status, HER2/neu status, histological grade, and number of lymph node metastases) or treatment modalities (hormone therapy, chemotherapy, and radiotherapy), so we were unable to conduct further factorial analyses for outcomes.