Abstract
Molecular subtyping of breast cancer may provide additional prognostic information regarding patient outcome. The epidermal growth factor receptor (HER2) overexpressing breast cancers are designated as HER2-postive (HER2+) breast cancer and carry a particularly unfavorable prognosis. We present two cases of HER2-postive metastatic breast cancer (MBC) who are found to be a challenge to treat, especially due to the occurrence of brain metastasis. Trastuzumab-based therapy improves clinical outcomes, even if the patient has undergone multi-line treatment. These case reports also emphasize the importance of retesting HER2 status because it can be discordance in receptor status between primary and recurrent breast cancer.