Will you continue anti-estrogen therapy in the setting of initiation of TDM-1 for patients with metastatic ER+/HER2+ breast cancer?

The answer to this question has not been well studied, but the registration trials that led to the approval of T-DM1 (EMILIA and TH3RESA) did not use T-DM1 with concurrent hormonal therapy. Historically, we have avoided combining chemotherapy with hormonal therapy for breast cancer. This was in part due to a lack of clear benefit with tamoxifen and chemotherapy with trials conducted in the 1980's and in some studies, increased risk of thrombosis. Also, in the adjuvant setting, sequential chemoth...