ERBB2 and metastatic neoplasm: In addition, considering the high immunogenicity of HER2+ tumors and the preferable settings in which immunotherapy could be employed (presence of tumor, early lines in metastatic disease), HER2+ breast cancer may represent a fertile soil (i.e., availability of tumor tissue, fast clinical impact) also to test newer immunotherapies agents and to expand the knowledge of possible mechanisms to overcome immunotherapy resistance.