Zinc and copper levels in bladder cancer: a systematic review and meta-analysis

It is well documented that oxidative stress is involved in the pathogenesis of bladder cancer. Zinc (Zn) and copper (Cu) are important components of antioxidants. However, the association between Zn or Cu levels and bladder cancer remains elusive. The present study was designed to investigate the alteration of serum and urinary levels of Zn or Cu in bladder cancer patients compared with controls by performing a systematic review. We searched the PubMed, Embase, and Cochrane databases from January 1990 to March 2013 to identify studies that met our predefined criteria. Six studies were included. Bladder cancer patients demonstrated significantly lower levels of serum Zn (three studies, random effects standard mean deviation (SMD): -1.072, 95 % CI: -1.489 to -0.656, P <0.0001), markedly higher levels of serum Cu (three studies, random effects SMD: 1.069, 95 % CI: 0.302 to 1.836, P = 0.006) and urinary Zn (three studies, random effects SMD: 2.114, 95 % CI: 0.328 to 3.899, P = 0.02) compared with controls. No obvious difference was observed in urinary Cu levels between bladder cancer patients and controls (two studies, random effects SMD: 0.153, 95 % CI: -0.244 to 0.55, P = 0.449). No evidence of publication bias was observed. In conclusion, the disorder of Zn and Cu is closely associated with bladder cancer. Frequent monitoring and early intervention should be recommended.