Unfavorable Drug Interactions in Targeted Breast Cancer Therapy

Trastuzumab is used to treat HER2-positive breast cancer; erythropoietin (EPO) is used to alleviate chemotherapy-associated side effects. In this issue of Cancer Cell, Liang et al. show that many breast tumors express EPO receptor (EpoR), whose activation by EPO recovers signaling pathways downregulated by trastuzumab, thereby blunting trastuzumabʹs therapeutic effect.