Increased expression of miR-222 is associated with poor prognosis in bladder cancer

Background: MicroRNA-222 (miR-222) has been shown to play a potential oncogenic role in bladder cancer. The aim of this study was to evaluate the expression of miR-222 in bladder cancer and its potential relevance to clinicopathological characteristics and patient survival. Methods: Surgical specimens of cancer tissue and adjacent normal tissue were obtained from 97 patients with bladder cancer. The relative expression levels of miR-222 in the cancer and the normal adjacent tissue were measured by quantitative reverse-transcriptase PCR. We analyzed their correlation with clinicopathological parameters and prognostic value. Results: The expression level of miR-222 was significantly higher in tumor tissues than in corresponding non-cancerous tissues (5.46 +/- 1.45 versus 1.92 +/- 0.65, P < 0.0001), and a high expression of miR-222 was found to be significantly associated with tumor grade (P = 0.003) and tumor stage (P = 0.005). The miR-222 expression level was classified as high or low in relation to the median value (cutoff value = 5.15). Kaplan-Meier analysis showed that patients with higher levels of miR-222 had significantly poorer survival than those with lower expression of this miRNA in patients, with a 5-year overall survival of 29.53% and 52.75%, respectively (P = 0.0034). In the multivariate Cox proportional hazards analysis, which included miR-222 level, tumor grade, tumor stage, and tumor number, high miR-222 expression was independently associated with poor survival (P < 0.001; hazard ratio 6.17; 95% CI 2.33 to 10.39). Conclusion: miR-222 overexpression is involved in the poor prognosis of bladder cancer and can be used as a biomarker for selection of cases requiring special attention.