Metformin in breast cancer: preclinical and clinical evidence

Metformin, a well-acknowledged biguanide, safety profile and multiaction drug with low cost for management of type 2 diabetes, makes a first-class candidate for repurposing. The off-patent drug draws huge attention for repositioned for anticancer drug delivery recently. Still few unanswered questions are challenging, among them one leading question; can metformin use as a generic therapy for all breast cancer subtypes? And is metformin able to get over the problem of drug resistance? The review focused on the mechanisms of metformin action specifically for breast cancer therapy and overcoming the resistance; also discusses preclinical and ongoing and completed clinical trials. The existing limitation such as therapeutic dose specifically for cancer treatment, resistance of metformin in breast cancer and organic cation transporters heterogeneity of the drug opens up a new pathway for improved understanding and successful application as repurposed effective chemotherapeutics for breast cancer. However, much more additional research is needed to confirm the accurate efficacy of metformin treatment for prevention of cancer and its recurrence.