ABSTRACT
Type II diabetes is associated with cancer risk in the general population but has not been well studied as a risk factor for subsequent malignancies among cancer survivors. We investigated the association between diabetes and subsequent cancer risk among older (66-84 years), 1-year breast cancer survivors within the linked Surveillance Epidemiology and End Results (SEER)-Medicare database using Cox regression analyses to quantify hazard ratios (HR) and corresponding 95% confidence intervals (95% CI). Among 133â324 women, 29.3% were diagnosed with diabetes before or concurrent with their breast cancer diagnosis, and 10â452 women developed subsequent malignancies over a median follow-up of 4.3 years. Diabetes was statistically significantly associated with liver (HR = 2.35, 95% CI = 1.48 to 3.74), brain (HR = 1.94, 95% CI = 1.26 to 2.96), and thyroid cancer risks (HR = 1.38, 95% CI = 1.01 to 1.89). Future studies are needed to better understand the spectrum of subsequent cancers associated with diabetes and the role of diabetes medications in modifying subsequent cancer risk, alone or in combination with cancer treatments.
Subject(s)
Breast Neoplasms , Cancer Survivors , Diabetes Mellitus, Type 2 , Proportional Hazards Models , SEER Program , Humans , Female , Aged , Breast Neoplasms/epidemiology , Breast Neoplasms/etiology , Aged, 80 and over , Cancer Survivors/statistics & numerical data , Diabetes Mellitus, Type 2/complications , Diabetes Mellitus, Type 2/epidemiology , United States/epidemiology , Risk Factors , Liver Neoplasms/epidemiology , Liver Neoplasms/etiology , Thyroid Neoplasms/epidemiology , Thyroid Neoplasms/etiology , Brain Neoplasms/epidemiology , Brain Neoplasms/etiology , Medicare/statistics & numerical data , Neoplasms, Second Primary/epidemiology , Neoplasms, Second Primary/etiologyABSTRACT
BACKGROUND: Metformin is among the most widely used antidiabetics medications because of its minimal toxicity, favorable safety profile, availability, and low cost. In addition to its role in diabetes management, metformin may reduce cancer risk. METHODS: We conducted a comprehensive systematic review and meta-analysis to investigate the association between metformin use and cancer risk, with evaluation by specific cancer type when possible. Applicable studies were identified in PubMed/MEDLINE, Embase, Cochrane Library, Web of Science, and Scopus from inception through March 7, 2023, with metformin use categorized as "ever" or "yes" and a cancer diagnosis as the outcome. Article quality was evaluated using National Heart, Lung, and Blood Institute guidelines, and publication bias was evaluated using the Egger test, Begg test, and funnel plots. Pooled relative risk (RR) estimates were calculated using random-effects models, and sensitivity analysis was completed through leave-one-out cross-validation. RESULTS: We included 166 studies with cancer incidence information in the meta-analysis. Reduced risk for overall cancer was observed in case-control studies (RR = 0.55, 95% confidence interval [CI] = 0.30 to 0.80) and prospective cohort studies (RR = 0.65, 95% CI = 0.37 to 0.93). Metformin use was associated with reduced gastrointestinal (RR = 0.79, 95% CI = 0.73 to 0.85), urologic (RR = 0.88, 95% CI = 0.78 to 0.99), and hematologic (RR = 0.87, 95% CI = 0.75 to 0.99) cancer risk. Statistically significant publication bias was observed within the studies (Egger P < .001). CONCLUSIONS: Metformin may be associated with a decreased risk of many cancer types, but high heterogeneity and risk of publication bias limit confidence in these results. Additional studies in populations without diabetes are needed to better understand the utility of metformin in cancer prevention.
