title: The effect of metformin on mortality following cancer among patients with diabetes.
abstract: Diabetes may be a risk factor for cancer and is associated with worse cancer outcomes. Metformin may reduce cancer risk; however, its effect on mortality following cancer remains less clear. EMBASE and Medline were searched through February 10, 2014, for studies reporting an adjusted risk estimate for the effect of metformin therapy on mortality following cancer among diabetic patients. Random-effects models were used to obtain summary HR for the association between metformin and all-cause and cancer-specific mortality. Twenty-one observational studies were meta-analyzed in the primary analysis. Metformin was associated with a reduction in all-cause mortality [HR, 0.73; 95% confidence intervals (CI), 0.64-0.83] and cancer-specific mortality (HR, 0.74; 95% CI, 0.62-0.88). Subgroup analyses by cancer site showed a significant reduction in mortality for colon cancer (four studies, HR, 0.65; 95% CI, 0.56-0.76) but not for breast and prostate cancers. Observational studies indicate that metformin exposure at cancer diagnosis may be associated with a reduction in mortality. However, these findings need to be interpreted with caution as methodologic limitations of individual studies may have introduced biases in these findings. Our results emphasize the need for well-designed studies to further understand the relationship between metformin and survival following cancer.
authors.affiliation: Women's College Research Institute, Women's College Hospital, Toronto, Ontario, Canada. iliana.lega@wchospital.ca.
authors.forename: Iliana C
authors.initials: IC
authors.lastname: Lega
authors.affiliation: University of Toronto, Institute of Health, Policy, and Management, Toronto, Ontario, Canada. Mount Sinai Hospital, Toronto, Ontario, Canada.
authors.forename: Prakesh S
authors.initials: PS
authors.lastname: Shah
authors.affiliation: Division of Urology and Davidoff Cancer Center, Petah-Tikva, Israel.
authors.forename: David
authors.initials: D
authors.lastname: Margel
authors.affiliation: Department of Clinical Epidemiology and Biostatistics, McMaster University, Hamilton, Ontario, Canada.
authors.forename: Joseph
authors.initials: J
authors.lastname: Beyene
authors.affiliation: Women's College Research Institute, Women's College Hospital, Toronto, Ontario, Canada. University of Toronto, Institute of Health, Policy, and Management, Toronto, Ontario, Canada.
authors.forename: Paula A
authors.initials: PA
authors.lastname: Rochon
authors.affiliation: Women's College Research Institute, Women's College Hospital, Toronto, Ontario, Canada. University of Toronto, Institute of Health, Policy, and Management, Toronto, Ontario, Canada.
authors.forename: Lorraine L
authors.initials: LL
authors.lastname: Lipscombe
mesh_terms: D003924:Diabetes Mellitus, Type 2 / Q000188:drug therapy*; D006801:Humans; D007004:Hypoglycemic Agents / Q000627:therapeutic use*; D008687:Metformin / Q000627:therapeutic use*; D009369:Neoplasms / Q000150:complications* / Q000401:mortality*
chemical_list: D007004:Hypoglycemic Agents; D008687:Metformin