Clinical overview of metronomic chemotherapy in breast cancer.

Over 15 years ago, low-dose metronomic chemotherapy was shown to induce disease control in patients with advanced-stage breast cancer with a lower incidence of adverse events compared with conventional maximum tolerated dose chemotherapy. Good response rates have been seen in heavily pre-treated patients for whom limited treatment options are available. Most patients prefer oral therapy and metronomic chemotherapy is a convenient alternative in patients with advanced-stage disease in which minimal toxicity and good tumour control are the overall aims of treatment. The addition of metronomic protocols to standard neoadjuvant chemotherapy regimens has produced promising pathological complete response rates. Ongoing trials including the SYSUCC-001 trial in patients with triple-negative breast cancer and the IBCSG 22-00 trial that is assessing a cyclophosphamide-methotrexate maintenance regimen after standard adjuvant therapy in hormone receptor-negative disease, will clarify the value of adding this approach to conventional therapies. The low cost associated with metronomic chemotherapy represents an opportunity for the utilization of this treatment option, especially in developing countries, and poses a challenge for the launch of large trials sponsored by industry. Using breast cancer as the principal example, we discuss the key clinical advances in this area, including new trial design, appropriate patient and end point selection, as well as the evolving rationale for metronomic chemotherapy combinations.