Maintenance treatment of trastuzumab for patients with advanced breast cancer to achieve long term survival: two case reports and literature review.

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.