ERBB2 and breast cancer: Future clinical trials will be designed to answer questions such as the role of omitting upfront WBRT and giving SRS alone for a single metastasis, the benefit of administering prophylactic cranial irradiation to highly metastatic cancers such as HER2+ breast cancer patients, the value of using hippocampal sparing techniques, and the addition of radiosensitizers to enhance WBRT.