Metronomic chemotherapy for patients with metastatic breast cancer: Review of effectiveness and potential use during pandemics.

Metronomic chemotherapy (M-CT) is defined as dose dense administration of chemotherapy at lower doses than maximum tolerated dose but at shorter free intervals, to obtain a near continuous exposure of cancer cells to those potentially effective drugs. M-CT is a useful strategy to obtain response, overcome resistance and reduce side effects, with low costs. This review will focus on the use of M-CT in advanced breast cancer (ABC). Cytostatic and cytotoxic effect on cancer cells, the anti-angiogenic and the immunomodulatory effects are its main mechanisms of actions. Many clinical trials proved the efficacy and tolerability of different monotherapies and combinations of chemotherapeutic agents administered in metronomic doses and frequencies in ABC. M-CT is a reasonable option for second and later lines of chemotherapy in metastatic breast cancer including those with prior anthracycline or taxane exposure, older patients and patients with comorbidities, and even as first-line in certain groups of patients. The acceptable efficacy and low toxicity of oral metronomic chemotherapy makes it a reasonable option during COVID-19 pandemic as well as in the post-COVID era which is projected to last for some time.