Metronomic Chemotherapy for Metastatic Breast Cancer

Background: As disease control and quality of life play a leading role in metastatic breast cancer (MBC), metronomic chemotherapy (MCT) is gaining popularity alongside conventional chemotherapy (CCT) and targeted therapies. Summary: MCT, defined as continuous administration of low-dose chemotherapeutic agents, is accepted as a therapy that exerts its effects via immunomodulation, anti-angiogenesis and direct cytotoxic effects. Oral administration of MCT is safe, easy to handle, and allows for flexible drug dosing. Dose accumulations associated with non-tolerable side effects are rare, so the medication can be administered for longer periods of time. Patients with hormone receptor (HR)-positive, human epidermal growth factor receptor 2 (HER2)-negative metastatic disease resistant to endocrine-based therapy and not requiring rapid tumor response are generally suitable for MCT. However, MCT may also be promising in patients with triple-negative and HER2-positive tumors without aggressive disease who prefer a lower toxicity profile compared to CCT. The most commonly used agents are cyclophosphamide (CTX), methotrexate (MTX), capecitabine (CAPE), and vinorelbine (VRL), whereby a combination of agents is frequently applied. Key Messages: Based on the growing body of evidence, MCT can be considered as a suitable treatment option in selected MBC patients. Nevertheless, there is an urgent need for randomized controlled trials comparing MCT with CCT, but also with best supportive care. Due to the multimodal mechanisms of action, the combination with targeted and immunological therapies may represent a new promising approach for the treatment of MBC.