The authors of the METAL (METformin in Advanced Lung Cancer) study [37], which was a phase I-II trial, hypothesized that the administration of metformin to non-diabetic patients may revert resistance to gefitinib, which is a selective epidermal growth factor receptor (EGFR) and tyrosine kinase inhibitor applied in non-small cell lung cancer. Here, EGFR is linked to lung cancer.