Type 2 diabetes mellitus does not increase the risk of multiple myeloma: a systematic review and meta-analysis

Background: Epidemiological studies have shown that patients with type 2 diabetes mellitus (T2DM) are at a higher risk of secondary tumors. However, no consensus has been made about whether T2DM can increase the risk of multiple myeloma (MM). Methods: We searched the databases of PubMed, Cochrane Library and EMBASE and cross-checked the bibliography. Data quality was assessed using the Newcastle-Ottawa scale (NOS). Heterogeneity was calculated as the odds ratio (OR) using a random-effects model. Data were analyzed using Stata version 12.0 software. Results: A total of 13 articles were selected into this meta-analysis. Initially, we found that diabetic patients had a higher risk of myeloma than non-diabetic patients (OR=1.60, 95% CI: 1.13-2.26, I-2=98%, P=0.000). But the data in these articles were highly heterogeneous (I-2>75%). Therefore, eight of the included articles showed a moderate heterogeneity (I-2=71.6%). We used Galbraith heterogeneity map to analyze the causes of heterogeneity. Two articles with high heterogeneity were excluded. Then, we found the heterogeneity of the left six articles was reduced from moderate to mild (I-2=45.9%, P=0.100). The final results of this meta-analysis showed that T2DM was not a risk factor for increased incidence of MM (OR=1.05, 95% CI: 0.83-1.33, I-2=45.9%, P=0.100). Also, the subgroup analysis (case-control studies vs. cohort studies) showed no statistical difference (OR=1.19, 95% CI: 0.76-1.85, I-2=1%, P=0.364; OR=1.00, 95% CI: 0.75-1.33, I-2=71.2%, P=0.031; respectively). Conclusions: T2DM is not a risk factor for the increased incidence of MM, a finding that should be validated with more strictly designed randomized controlled trials (RCTs).