Anti-tumor effects of metformin on head and neck carcinoma cell lines: A systematic review

Metformin is commonly used for treating type 2 diabetes, and may also reduce cancer risk. Previous studies have demonstrated the association between metformin use and a decreased risk of head and neck cancer. Therefore, the aim of the present systematic review was to summarize the available literature on the in vitro anti-tumor effects of metformin on head and neck squamous cell carcinoma (HNSCC). Research studies were obtained from Cochrane Library, Embase, LILACS, MEDLINE and PubMed databases, without time or language restrictions. Only in vitro studies analyzing the effects of metformin on HNSCC cell lines were included. The authors methodically appraised all the selected studies according to the Grading of Recommendations Assessment, Development and Evaluation method to make a judgment of the evidence quality. Of the 388 identified reports, 11 studies met the inclusion criteria and were used for qualitative analysis. These studies demonstrated that metformin is important in inhibiting cell proliferation, inducing G0/G1 cell cycle arrest and apoptosis, and in regulating proteins involved in carcinogenesis pathways, which corroborates its potential in vitro anti-tumor effects. The present systematic review highlights the biological mechanisms of metformin used alone or together with traditional therapies for cancer. Though very limited, currently available preclinical evidence shows that metformin exerts a potential effect on head and neck carcinoma.