Effects of metformin on survival outcomes of lung cancer patients with type 2 diabetes mellitus: a meta-analysis

Anti-cancer effect of metformin on different kinds of lung cancer has been studied frequently. However, the association between metformin and the prognosis of lung cancer in type 2 diabetes patients is still controversial. An electronic search was conducted using PubMed/Medicine, EMBASE and Cochrane library databases. Statistical analyses were carried out using either random-effects or fixed-effects models according to the heterogeneity examined by I (2) statistics. Six studies involving 2350 patients were included in the current meta-analysis. In all, the pooled HR of overall survival (OS) was 0.90 (95 % CI 0.84-0.96; P = 0.003). Sub-group analysis showed that when stratified by region the HR of OS was 0.52 (95 % CI 0.31-0.87; P = 0.012) and 0.86 (95 % CI 0.67-1.11, P = 0.361) for Asian and Western countries. When stratified by study design, the HR of OS was 0.78 (95 % CI 0.52-1.15, P = 0.206) and 0.82 (95 % CI 0.59-1.16, P = 0.264) for cohort and medical data-based studies. When stratified by lung cancer subtype, HR of OS was 0.52 (95 % CI 0.31-0.87; P = 0.012), 1.06 (95 % CI 0.51-2.19; P = 0.878) and 0.82 (95 % CI 0.59-1.16; P = 0.264) for SCLS, NSCLC and non-divided subtypes, respectively. Metformin use may associate with a good prognosis in lung cancer patients with type 2 diabetes but the effect was modest. However, it could achieve benefits in a selective sub-group of lung cancer patients especially in SCLC patients from Asian. Further studies are warranted to confirm this efficacy.